Abstract Detail

Comparative Genomics/Transcriptomics

Gilman, Ian S. [1], Moreno-Villena, Jose [1], Zachary, Lewis [1], Goolsby, Eric [2], Edwards, Erika J. [1].

Gene co-expression reveals evolutionarily conserved and distinct photosynthetic networks in C4+CAM Portulaca.

C4 and Crassulacean acid metabolism (CAM) have been considered as largely independent photosynthetic adaptations in spite of sharing key biochemical pathways. Portulaca is a geographically widespread clade of over 100 annual and perennial flowering plant species that primarily use C4 photosynthesis, but facultatively exhibit CAM when drought stressed-a photosynthetic system known as C4+CAM. Anatomical, biochemical, and gene regulatory constraints have been proposed to explain the rarity of C4+CAM lineages, but these have not been deeply explored. We sequenced the genome of P. amilis and sampled mRNA from P. amilis and P. oleracea over the course of a CAM-induction experiment. Gene co-expression network analyses identified core sets of genes involved in C4 and CAM shared and unique to both Portulaca species, as well as putative transcription factors and associated cis-regulatory motifs in P. amilis. A conserved set of co-expressed genes indicated that CAM evolved by linking phosphoenolpyruvate carboxylase (PEPC) to starch turnover during the day-night transition. Preservation of this co-expression module regardless of water status suggests that Portulaca species constitutively operate a weak CAM cycle that is ramped up upon drought. C4 and CAM used mutually exclusive sets of paralogs for primary carbon fixation and it is likely that nocturnal CAM malate stores are shuttled into diurnal C4 decarboxylation pathways. C4 likely evolved de novo in Portulaca through co-option of redundant paralogs and the diurnal portion of CAM has been largely integrated into C4 photosynthesis. Thus, the ancestral CAM system did not strongly constrain C4 gene expression evolution because photosynthetic gene networks are not co-regulated for both C4 and CAM.

Related Links:
Walk-though of genome annotation and transcriptomic analyses

1 - Yale University, Ecology and Evolutionary Biology, 165 Prospect St, Osborn Memorial Labs, New Haven, CT, 06511, USA
2 - University Of Central Florida, 886 N Jerico Dr, BLDG20, BL301, Casselberry, FL, 32707, United States

Keywords:
photosynthsis
CAM
C4
transcriptomics
co-expression network
Portulaca
genomics.

Presentation Type: Oral Paper
Session: CGT2, Comparative Genomics/Transcriptomics II
Location: /
Date: Tuesday, July 20th, 2021
Time: 12:45 PM(EDT)
Number: CGT2002
Abstract ID:233
Candidate for Awards:None