The transcriptomic responses of C4 grasses to subambient CO2 and low light are largely species specific and only refined by photosynthetic subtype.

Abstract

Three subtypes of C4 photosynthesis exist (NADP-ME, NAD-ME and PEPCK), each known to be beneficial under specific environmental conditions. However, the influence of photosynthetic subtype on transcriptomic plasticity, as well as the genes underpinning this variability, remain largely unknown. Here, we comprehensively investigatethe responses ofsix C4 grass species, spanning all three C4 subtypes, to two controlled environmental stresses: low light (200µmolm-2 sec-1 ) and glacial CO2 (subambient; 180ppm). We identify a susceptibility within NADP-ME species to glacial CO2 . Notably, althoughglacial CO2 phenotypes could be tied to C4 subtype, biochemical and transcriptomic responses to glacial CO2 werelargelyspecies specific. Nevertheless, we were able to identify subtype specific subsets of significantly differentially expressed transcripts which link resource acquisition and allocation to NADP-ME speciessusceptibility to glacial CO2 . Here, low light phenotypes werecomparableacross species with no clear subtype response,while again, transcriptomic responses to low light were largely species specific. However,numerous functional similarities were notedwithin the transcriptomic responses to low light, suggesting these responses are functionallyrelatively conserved. Additionally, PEPCK species exhibited heightened regulation of transcripts related to metabolism in response to both stresses, likely tied to their C4 metabolic pathway. These results highlight the influence that both species and subtype can have on plant responses to abiotic stress, building on our mechanistic understanding of acclimation within C4 grasses and highlighting avenues for future crop improvements.