Abstract Detail

Evolution of Plant Chemical Diversity: Renaissance of comparative biochemistry

Heyduk, Karolina [1], Leebens-Mack, Jim [2].

Comparative RNAseq of independent origins of Crassulacean acid metabolism in the Agavoideae.

Photosynthetic biochemistry is often considered quite stable, given its importance for life on earth. But multiple modifications to the photosynthetic machinery, particularly in the carbon reactions, have evolved in flowering plants to circumvent abiotic stress. One such modification, Crassulacean acid metabolism (CAM), is thought to have evolved in response to water limitation. CAM plants uptake CO₂ from the atmosphere at night, when evapotranspiration rates are lower. CO₂ is stored temporarily as malic acid in the vacuoles and is subsequently decarboxylated in the daytime behind closed stomata. The temporal modification of CO₂ capture in CAM plants results in high concentrations of CO₂ around RuBisCO, thereby reducing photorespiration and increasing water use efficiency. CAM has evolved roughly 35 independent times in flowering plants and is found in 7% of all species, implying the transition between C₃ and CAM may not be uncommonly difficult. Indeed, all required CAM genes are found in C₃ species, and the transition between CAM and C₃ is thought to be a matter of rewiring timing of expression. To better understand how these biochemical pathways have been rewired in CAM plants, we compared gene expression collected from time course RNAseq in three independent origins of CAM in the subfamily Agavoideae (Asparagaceae): Agave sensu lato, Yucca, and Hesperaloe. Physiological data paired with RNAseq was collected across the day-night cycle in strong CAM, weak CAM, and C₃ species. Expression analysis reveals that alternative copies of some genes have been independently recruited into the CAM pathway in different origins of CAM. And although the levels of expression are quite clearly different for canonical CAM genes in C₃ and CAM species, a number of C₃ species examined here have similar timing of expression of CAM pathway genes as their close CAM relatives, despite not using any CAM photosynthesis. Combined our results indicate that the Agavoideae may have been pre-disposed to evolve CAM both physiologically and genetically, although further investigations pairing RNAseq with metabolite abundance across the subfamily are needed to fully resolve the mechanism of CAM evolution in this lineage.

1 - University Of Georgia, Plant Biology, 2502 Miller Plant Sciences, Athens, GA, 30602, United States
2 - University Of Georgia, Plant Biology, 2101 Miller Plant Sciences, Athens, GA, 30602, United States

Keywords:
photosynthesis
transcriptomics
yucca
agave
CAM.

Presentation Type: Symposium Presentation
Session: SY5, Evolution of Plant Chemical Diversity: Renaissance of comparative biochemistry
Location: 102/Mayo Civic Center
Date: Wednesday, July 25th, 2018
Time: 9:15 AM
Number: SY5004
Abstract ID:225
Candidate for Awards:None