American Society of Plant Biology Conference – Montreal July 14-18

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Time to get ready for the ASPB meeting in Montreal. Find us there.  https://www.eventscribe.com/2018/ASPB/PosterTitles.asp?pfp=PosterTitles

400-005 – Characterization of a Synthetic Metabolic Cycle to Enhance Carbon Fixation in Plants

Presenter:  Nathan Wilson

Tuesday, Jul 17

1:30 PM – 3:00 PM

 

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the catalytically “inefficient” enzyme of the Calvin-Benson cycle that is responsible for fixing atmospheric CO2 in plants. RuBisCO’s oxygenase activity causes as much as a 30% loss of fixed carbon and energy through photorespiration. This process diminishes plant productivity and is most detrimental in C3 crops, such as soybean and canola. It has been estimated that a 5% decrease of photorespiration would translate into a ~$540 million gain in annual crop production. Metabolic engineering approaches to design CO2 fixation cycles independent of RuBisCO have so far only been tested in vitro. We have engineered a synthetic CO2 fixation cycle inspired by bacterial autrotrophs. Our cycle is a condensed reverse Tricarboxylic Acid (crTCA) cycle which is modeled to achieve carbon fixation with a 20% lower energetic cost than the Calvin-Benson cycle. The crTCA cycle consists of 5 bacterial enzymes that utilize succinate and CO2 to generate glyoxylate and regenerate the carboxylation substrate. Based on successful in vitro analysis of the cycle, we have codon-optimized the bacterial genes for expression in plants. We have generated and have transformed constructs of those bacterial genes targeted to the chloroplast into Camelina sativa and have demonstrated stable expression. Preliminary analyses of crTCA lines show higher CO2assimilation rates and increased biomass. This suggests that the cycle can not only function but contributes to CO2 fixation in vivo. Our primary goals are to determine if supplementing RuBisCO via synthetic pathways is a viable approach to increasing plant productivity and to learn how this engineered pathway contributes to endogenous plant metabolism. This research was funded by the Department of Energy (ARPAe AR-0000207 & BER DE-SC0018269).

500-049 – Repression of the Cell Wall Invertase Inhibitors increase seed yield in Camelina sativa

Presenter:  Brianne Edwards

Tuesday, Jul 17

1:30 PM – 3:00 PM

While Camelina sativa has great potential as a bioenergy crop due to its high seed oil content and low requirements for agricultural input of water and fertilizer, its yields are too low to compete with other current oil seed crops. To increase seed yield in Camelina, we have engineered the regulation of apoplasmic loading of sucrose into the phloem. Sucrose as a product of photosynthesis is transported from the photosynthetic active (green) source tissues like leaves to the non-photosynthetic sink tissues like roots, flowers and seed via the phloem. Export and import of sucrose between phloem and sink or source tissues is at least in part controlled by Cell Wall Invertases (CINV). These CINVs are regulated by proteinaceous inhibitors, the Cell Wall Invertase Inhibitors (CWIIs). These CWII regulate the CINV activity by binding to the active side in response to apoplasmic sucrose concentration and pH. We have generated CWIIs silenced RNAi lines to understand the role of the inhibitors on the physiology and gene expression in source tissue. Plants with reduced CWII protein developed faster, had higher vegetative biomass (>20%), higher rates of photosynthesis, and increased seed yield (40-80%). RNAseq analysis of CWII RNAi lines showed over 400 differentially expressed genes when compared with wild type transcriptome data. These results will allow us to characterize overall changes in the expression of genes in metabolic pathways involved in the phenotypic changes. Acknowledgement: This research is funded by DOE awards AR-0000207 and DE-SC0018269.

1000-071 – Evaluating components of the Common Symbiosis Pathway in nonmycorrhizal plants

Presenter:  Eli Hornstein

Tuesday, July 17th

1:30 PM – 3:00 PM

Arbuscular mycorrhizae (AM) are central to rhizosphere relations in the large majority of plant species. Via its impact on nutrient uptake and stress resistance this symbiosis therefore also underlies patterns of wild species distribution and domestic agricultural productivity. However, the mechanisms that permit plants to recognize, accept, and regulate colonization by fungal symbionts are not yet fully understood. This study uses knock-in of the mycorrhizae-necessary gene Interacting Protein of DMI3 (IPD3) in the nonmycorrhizal oilseed crop Camelina sativa (Brassicaceae) to help address both the above questions and the issue of why a small minority of plant species have lost the ability to form mycorrhizae at all. IPD3 is a member of the Common Symbiosis Pathway (CSP) which enables fungal signals to be received by the plant and transduced into transcriptional changes of genes directly implicated in cell restructuring and nutrient exchange. Putative orthologs of 11 genes belonging to the CSP were identified in Camelina by protein sequence and structural similarity. In mycorrhizal host plants IPD3 is an inducible transcription factor at the center of the transduction chain comprising those 11 genes. In contrast to the other CSP elements with which it interacts, no putative ortholog of IPD3 was identified in Camelina. To begin determining whether any of the remaining CSP orthologs retain their symbiotic function, 7 lines of Camelina bearing the IPD3 coding sequence from Medicago truncatula were generated. Transgenic lines are currently being phenotyped for their response to exposure to the model AM fungus Rhizophagus irregularis. Transgenic lines will also be compared to wildtype Camelina and Medicago for relative expression changes of the interacting CSP genes before and after insertion of IPD3, and with and without exposure to the symbiont. This work is supported by BER grant DE-SC0018269.