RT Journal Article SR Electronic T1 Quantitative variation within a species for traits underpinning C4 photosynthesis JF bioRxiv FD Cold Spring Harbor Laboratory SP 253211 DO 10.1101/253211 A1 Gregory Reeves A1 Pallavi Singh A1 Timo A. Rossberg A1 E. O. Deedi Sogbohossou A1 M. Eric Schranz A1 Julian M. Hibberd YR 2018 UL http://biorxiv.org/content/early/2018/01/25/253211.abstract AB Engineering C4 photosynthesis into C3 crops such as rice or wheat could substantially increase their yield by alleviating photorespiratory losses1,2. This objective is challenging because the C4 pathway involves complex modifications to the biochemistry, cell biology and anatomy of leaves3. Forward genetics has provided limited insight into the mechanistic basis of these characteristics and there have been no reports of significant quantitative intra-specific variation of C4 attributes that would allow trait-mapping4,5. Here we show that accessions of C4 Gynandropsis gynandra collected from locations across Africa and Asia exhibit natural variation in key characteristics of C4 photosynthesis. Variable traits include bundle sheath size and vein density, gas exchange parameters and carbon-isotope discrimination associated with the C4 state, but also abundance of transcripts encoding core enzymes of the C4 cycle. Traits relating to water use showed more quantitative variation than those associated with carbon assimilation. We propose variation in these traits likely adapted the hydraulic system for increased water use efficiency rather than improving carbon fixation, indicating that selection pressure may drive C4 diversity in G. gynandra by acting to modify water use rather than photosynthesis. As these accessions can be easily crossed and produce fertile offspring, our findings indicate that natural variation within a C4 species is sufficiently large to allow genetic-mapping of key anatomical C4 traits and regulators.