Local Adaptation Portends Tradeoffs Between Leaf Cooling and Hydraulic Risk in an Arid Land Riparian Tree Species (Populus Fremontii)

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Description
Climate change is making the arid southwestern U.S. (“Southwest”) warmer and drier. Decreases in water availability coupled with increases in episodic heat waves can pose extraordinary challenges for native riparian tree species to persist in their current ranges. However, the…

Climate change is making the arid southwestern U.S. (“Southwest”) warmer and drier. Decreases in water availability coupled with increases in episodic heat waves can pose extraordinary challenges for native riparian tree species to persist in their current ranges. However, the morpho-physiological mechanisms that these species deploy to cope with extreme temperature events are not well understood. Specifically, how do these species maintain leaf temperatures within a safe operational threshold in the extreme conditions found across the region? Morpho-physiological mechanisms influencing intraspecific local adaptation to thermal stress were assessed in Populus fremontii using two experimental common gardens. In a common garden located near the mid-point of this species’ thermal distribution, I studied coordinated traits that reflect selection for leaf thermal regulation through the measurement of 28 traits encompassing four different trait spectra: phenology, whole-tree architecture, and the leaf and wood economic spectrum. Also, I assessed how these syndromes resulted in more acquisitive and riskier water-use strategies that explained how warm-adapted populations exhibited lower leaves temperatures than cool-adapted populations. Then, I investigated if different water-use strategies are detectable at inter-annual temporal scales by comparing tree-ring growth, carbon, and oxygen isotopic measurements of cool- versus warm-adapted populations in a common garden located at the extreme hottest edge of P. fremontii’s thermal distribution. I found that P. fremontii’s adaptation to the extreme temperatures is explained by a highly intraspecific specialized trait coordination across multiple trait scales. Furthermore, I found that warmer-adapted populations displayed 39% smaller leaves, 38% higher midday stomatal conductance, reflecting 3.8 °C cooler mean leaf temperature than cool-adapted populations, but with the tradeoff of having 14% lower minimum leaf water potentials. In addition, warm-adapted genotypes at the hot edge of P. fremontii’s distribution had 20% higher radial growth rates, although no differences were detected in either carbon or oxygen isotope ratios indicating that differences in growth may not have reflected seasonal differences in photosynthetic gas exchange. These studies describe the potential effect that extreme climate might have on P. fremontii’s survival, its intraspecific responses to those events, and which traits will be advantageous to cope with those extreme environmental conditions.
Date Created
2022
Agent

The Effects of 2,3-butanediol on Arabidopsis and Various Crops

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Description
Climate change has the potential to reduce the amount of land that is suitable for crop growth. Such changes may cause food shortages, which would most likely disproportionately affect the poorest regions of the world. While GMO crops showed potential…

Climate change has the potential to reduce the amount of land that is suitable for crop growth. Such changes may cause food shortages, which would most likely disproportionately affect the poorest regions of the world. While GMO crops showed potential to increase crop yield and agricultural efficiency, significant public pushback has led to a search for alternative methods to generate similar results. Compounds produced by bacteria, such as 2,3-butanediol, offer a potential way to change the phenotypes of plants without the deliberate genomic changes involved in the development of GMOs which are often the subject of great controversy. These compounds influence how plants grow and function. Through precise application, the compounds could be used to improve crop yield and stress tolerance. While these effects are not completely understood, they may be due to changes in transcription and translation of certain proteins, the microbiome surrounding the plants and its interactions with the compounds, or other unknown factors. The compound 2,3-butanediol appears to increase biomass, lead to larger root systems and more root hairs, and increase germination rates in a variety of plants. All these traits are favorable for producing higher yields and enduring stress conditions. The phenotypes induced by this compound are similar to plants engineered to over express a type I proton pyrophosphatase. Plants treated with 2,3-butanediol offer a potential option to achieve the benefits of GMO crops without the attached social stigma.
Date Created
2019-12
Agent

Conjecture Regarding Posttranslational Modifications to the Arabidopsis Type I Proton-Pumping Pyrophosphatase (AVP1)

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Description

Agbiotechnology uses genetic engineering to improve the output and value of crops. Altering the expression of the plant Type I Proton-pumping Pyrophosphatase (H+-PPase) has already proven to be a useful tool to enhance crop productivity. Despite the effective use of…

Agbiotechnology uses genetic engineering to improve the output and value of crops. Altering the expression of the plant Type I Proton-pumping Pyrophosphatase (H+-PPase) has already proven to be a useful tool to enhance crop productivity. Despite the effective use of this gene in translational research, information regarding the intracellular localization and functional plasticity of the pump remain largely enigmatic. Using computer modeling several putative phosphorylation, ubiquitination and sumoylation target sites were identified that may regulate Arabidopsis H+-PPase (AVP1- Arabidopsis Vacuolar Proton-pump 1) subcellular trafficking and activity. These putative regulatory sites will direct future research that specifically addresses the partitioning and transport characteristics of this pump. We posit that fine-tuning H+-PPases activity and cellular distribution will facilitate rationale strategies for further genetic improvements in crop productivity.

Date Created
2017-09-12
Agent

Alternate Modes of Photosynthate Transport in the Alternating Generations of Physcomitrella Patens

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Description

Physcomitrella patens has emerged as a model moss system to investigate the evolution of various plant characters in early land plant lineages. Yet, there is merely a disparate body of ultrastructural and physiological evidence from other mosses to draw inferences…

Physcomitrella patens has emerged as a model moss system to investigate the evolution of various plant characters in early land plant lineages. Yet, there is merely a disparate body of ultrastructural and physiological evidence from other mosses to draw inferences about the modes of photosynthate transport in the alternating generations of Physcomitrella. We performed a series of ultrastructural, fluorescent tracing, physiological, and immunohistochemical experiments to elucidate a coherent model of photosynthate transport in this moss. Our ultrastructural observations revealed that Physcomitrella is an endohydric moss with water-conducting and putative food-conducting cells in the gametophytic stem and leaves. Movement of fluorescent tracer 5(6)-carboxyfluorescein diacetate revealed that the mode of transport in the gametophytic generation is symplasmic and is mediated by plasmodesmata, while there is a diffusion barrier composed of transfer cells that separates the photoautotrophic gametophyte from the nutritionally dependent heterotrophic sporophyte.

We posited that, analogous to what is found in apoplasmically phloem loading higher plants, the primary photosynthate sucrose, is actively imported into the transfer cells by sucrose/H[superscript +] symporters (SUTs) that are, in turn, powered by P-type ATPases, and that the transfer cells harbor an ATP-conserving Sucrose Synthase (SUS) pathway. Supporting our hypothesis was the finding that a protonophore (2,4-dinitrophenol) and a SUT-specific inhibitor (diethyl pyrocarbonate) reduced the uptake of radiolabeled sucrose into the sporangia. In situ immunolocalization of P-type ATPase, Sucrose Synthase, and Proton Pyrophosphatase – all key components of the SUS pathway – showed that these proteins were prominently localized in the transfer cells, providing further evidence consistent with our argument.

Date Created
2017-11-13
Agent

Differential Nucleotide Diversity and Linkage Disequilibrium Levels at Homoelogous Loci Associated with Fiber Traits in Cotton (G. barbadense L.)

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Description
The modern tetraploid species Gossypium barbadense L. (AD2) traces its origins to an allopolyploidy event between diploid progenitors G. raimondii (DT Genome, Americas) and G. herbaceum (AT Genome, Asia/Africa). In this study, nine fiber-related genes consisting of seven MYB transcription…

The modern tetraploid species Gossypium barbadense L. (AD2) traces its origins to an allopolyploidy event between diploid progenitors G. raimondii (DT Genome, Americas) and G. herbaceum (AT Genome, Asia/Africa). In this study, nine fiber-related genes consisting of seven MYB transcription factors, a cellulose synthase homolog, and a tubulin homolog were resequenced across 54 G. barbadense lines spanning the wild-to-domesticated spectrum. Tests for nucleotide diversity (π), linkage disequilibrium (LD), and Tajima’s D were performed to examine the extent to which evolutionary forces have acted on these nine loci in G. barbadense. Results indicated that the AT-genome loci had significantly higher levels of diversity and lower levels of LD relative to homoelogous loci from the DT-genome. Additionally, all loci showed signatures of a population size expansion after a bottleneck or selective sweep and/or purifying selection. As previously shown for a sister tetraploid taxa (G. hirsutum), gene conversion resulting from a DT-genome allele invasion into the AT-genome likely explains the higher levels of diversity and lower levels of intragenic LD in the AT-genome. Given the relatively very low level of genetic diversity in elite lines, introduction of novel alleles from wild, land race, or obsolete lines into modern Pima cotton breeding programs is needed to expand the narrow gene pool of G. barbadense for continual yield improvements.
Date Created
2013-05
Agent

Effects of Nitrogen Deficiency on 74 Breeding Lettuce Lines Derived from the Cross Parade vs. Pavane under Different Illumination Conditions

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The manner in which plants are able to acquire plant nitrate (NO3-) varies depending on a combination of distinct processes between "root high-and low-affinity NO-3 transporters and the proton gradient that is generated by the plasma membrane H+-ATPase" (Paez-Valencia et…

The manner in which plants are able to acquire plant nitrate (NO3-) varies depending on a combination of distinct processes between "root high-and low-affinity NO-3 transporters and the proton gradient that is generated by the plasma membrane H+-ATPase" (Paez-Valencia et al, 2013). In this study we analyzed the response to limiting nitrate (0.5 mM) of seventy-four breeding lettuce (Lactuca sativa) lines derived from the cross Parade vs. Pavane. Parade had an enhanced root acidification capacity when grown under Nitrate limitation in comparison to Pavane, which had a poor root acidification capacity. Two successive experiments were conducted under distinct environmental conditions to evaluate the performance of the different breeding lines based on their ability to grow under nitrogen limitation as an indirect measurement of their ability to take up nitrate. Specific parameters were established in order to properly classify strong and weak breading lines based on the following characterizations: 1) Average fresh shoots and roots weights; 2) Color of leaves (green vs. yellow); and 3) Root acidification capacity. In essence, the measurement of these parameters is would allow for the identification of breeding lines that demonstrated enhanced performance under Nitrate limitation in order to observe if their performance correlated with root acidification capacity. The breeding line's biomass, indicated by the average fresh shoots and roots weights, determined the plant's ability to uptake Nitrogen; whereas, large biomass values indicated Nitrogen uptake, low values indicated a low Nitrogen uptake (Javadiyan, 2008). To determine Nitrogen nutrition, the colors of the plants' leaves were observed throughout the duration of the study; a green color demonstrated appropriate Nitrogen nutrition, whereas as a yellow color identified Nitrogen deficiency (Yang, 2003). In addition to the nutrients that composed the media in the agar plates, a pH indicator (Bromocresol Purple Dye) was utilized to monitor root acidification; the purple indicator transformed into a yellow color upon the occurrence of acidification. In both experiments, a direct correlation between the root acidification capacity and the biomass of each breeding line could not be determined. Strong breeding lines were identified when they demonstrated large biomass measurements, which were obtained from the average fresh shoots and roots, and also a proper nitrogen nutrition status, which was shown through their green leaf phenotypic characteristics. These two characterizations were significantly prevalent in four breeding lines (B9, B17, C1, and C21), which on average outperformed the parental lines (Controls: P12 and P13).
Date Created
2013-05
Agent

Phenotypes associated with over-expression of type I H+-PPases: Is there a common mechanism?

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Description
Type I H+-PPase encoding genes, such as AVP1 (Arabidopsis thaliana), TsVP (Thellungiella halophilla), TaVP,( Triticum aestivum), and OVP1 (Oryza sativa) are highly conserved and.traditionally known to operate as vacuolar proton translocating pyrophosphatases. It is worth mentioning that Rocha-Facanha and de…

Type I H+-PPase encoding genes, such as AVP1 (Arabidopsis thaliana), TsVP (Thellungiella halophilla), TaVP,( Triticum aestivum), and OVP1 (Oryza sativa) are highly conserved and.traditionally known to operate as vacuolar proton translocating pyrophosphatases. It is worth mentioning that Rocha-Facanha and de Meis presented in vitro evidence with tonoplast fractions of maize coleoptiles and seeds consistent with the reverse function of the H+-PPase (1998). These authors suggested that given the appropriate thermodynamic conditions in vivo, the H+-PPase could operate as a system of energy conservation with a role in the maintenance of cytosolic PPi levels. Further evidence in support for a PPi-synthase activity of plant H+-PPases came from work done on tonoplasts from mature oranges where PPi synthesis was demonstrated when a ΔpH of 3 units was imposed (Marsh et al. 2000).

Futher research has shown that transgenics overexpressing type I H+-PPases develop more root and shoot biomass, and have enhanced rhizosphere acidification capacity than wild types. The increased root biomass suggests that previous reports describing the response of these plants to water scarcity as drought tolerance are incomplete. Larger root systems indicate that an important component of the response is drought resistance. The enhanced rhizosphere acidification capacity has also been associated with an increase in nutrient use efficiency, conferring a growth advantage under nitrogen and phosphorous deficient conditions.
While a vacuolar localized H+-PPase easily explains the salt tolerant phenotypes, it does little to provide a mechanism for an increase in root and shoot biomass and/or an augmented rhizosphere acidification capacity. Several groups have argued that higher levels and transport of the growth hormone auxin could be responsible for the above phenotypes. An alternative model focusing on the function of a plasma membrane bound H+-PPase in sieve elements and companion cells links these phenotypes with enhanced phloem sucrose loading and transport.
The following paper reviews publications in which the H+-PPase overexpression technology has been used since 2006 in an attempt to identify cues that could help us test the compatibility of the the proposed models with the actual data.
Date Created
2014-05
Agent

Characterization of Transgenic Arabidopsis thaliana Overexpressing a Type I H+ Pyrophosphatase and the Phloem Lipid-Associated Family Protein

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Description
Overexpression of AVP1 (Arabidopsis vacuolar pyrophosphatase), a type I H+ pyrophosphatase, results in greater biomass, possibly due to a function in sucrose transport within the phloem. Overexpression of the phloem lipid-associated family protein (PLAFP) was shown to increase the number…

Overexpression of AVP1 (Arabidopsis vacuolar pyrophosphatase), a type I H+ pyrophosphatase, results in greater biomass, possibly due to a function in sucrose transport within the phloem. Overexpression of the phloem lipid-associated family protein (PLAFP) was shown to increase the number of vascular bundles in Arabidopsis. Could these two phenotypes complement one another additively? In this work, double mutants overexpressing both AVP1 and PLAFP were characterized. These double mutants have enhanced biomass, greater leaf area, and a larger number of vascular bundles than the single mutant lines. Overexpression of PLAFP does not result in any increase in rhizosphere acidification capacity.
Date Created
2014-05
Agent

Approaches to engineering Synechocystis for biofuel production with emphasis on electron transport modifications

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Description
The basic scheme for photosynthesis suggests the two photosystems existing in parity with one another. However, cyanobacteria typically maintain significantly more photosystem I (PSI) than photosystem II (PSII) complexes. I set out to evaluate this disparity through development and analysis…

The basic scheme for photosynthesis suggests the two photosystems existing in parity with one another. However, cyanobacteria typically maintain significantly more photosystem I (PSI) than photosystem II (PSII) complexes. I set out to evaluate this disparity through development and analysis of multiple mutants of the genetically tractable cyanobacterium Synechocystis sp. PCC 6803 that exhibit a range of expression levels of the main proteins present in PSI (Chapter 2). One hypothesis was that the higher abundance of PSI in this organism is used to enable more cyclic electron flow (CEF) around PSI to contribute to greater ATP synthesis. Results of this study show that indeed CEF is enhanced by the high amount of PSI present in WT. On the other hand, mutants with less PSI and less cyclic electron flow appeared able to maintain healthy levels of ATP synthesis through other compensatory mechanisms. Reduction in PSI abundance is naturally associated with reduced chlorophyll content, and mutants with less PSI showed greater primary productivity as light intensity increased due to increased light penetration in the cultures. Another question addressed in this research project involved the effect of deletion of flavoprotein 3 (an electron sink for PSI-generated electrons) from mutant strains that produce and secrete a fatty acid (Chapter 3). Removing Flv3 increased fatty acid production, most likely due to increased abundance of reducing equivalents that are key to fatty acid biosynthesis. Additional components of my dissertation research included examination of alkane biosynthesis in Synechocystis (Chapter 4), and effects of attempting to overexpress fibrillin genes for enhancement of stored compounds (Chapter 5). Synechocystis is an excellent platform for metabolic engineering studies with its photosynthetic capability and ease of genetic alteration, and the presented research sheds light on multiple aspects of its fundamental biology.
Date Created
2017
Agent

Plant-made biologics: human butyrylcholinesterase mutants for the treatment of cocaine addiction-related diseases

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Description
Cocaine abuse affects millions of people with disastrous medical and societal consequences. Despite this, there is still no FDA-approved treatment to decrease the likelihood of relapse in rehabilitated addicts, and acute cocaine toxicity (overdose) is only symptomatically treated. Studies have…

Cocaine abuse affects millions of people with disastrous medical and societal consequences. Despite this, there is still no FDA-approved treatment to decrease the likelihood of relapse in rehabilitated addicts, and acute cocaine toxicity (overdose) is only symptomatically treated. Studies have demonstrated a promising potential treatment option with the help of the human serum enzyme butyrylcholinesterase (BChE), an enzyme capable of breaking down cocaine into biologically inactive side products. This activity of wild-type BChE, however, is relatively low. This prompted the design of variants of BChE which exhibit significantly improved catalytic activity against cocaine. Plants were used as a sustainable, scalable, affordable platform system to produce large amounts of human biologics such as these cocaine hydrolase variants of BChE. Using a tobacco relative, Nicotiana benthamiana, recombinant enzymes can be produced at quantities relevant to clinical use with desired kinetic properties. Next, the ability of the most promising plant-produced cocaine super hydrolase, pCocSH, to counter the lethal effects of cocaine overdose in vivo was tested. These studies revealed that this plant-produced enzyme can protect mice from an otherwise lethal dose of cocaine. Most excitingly, it was found that pCocSH can rescue mice from overdose when given immediately after the onset of cocaine-induced seizures. These studies provide in vitro and in vivo proof-of-principle for a promising plant-derived biologic to be used as a pharmacokinetic-based treatment for cocaine addiction-related diseases such as overdose.
Date Created
2015
Agent
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