Toward elucidation of shoot-root communications involved in the developmental transition of C۳ to C۴ photosynthesis by comparative transcriptome analysis of hypocotyls in Halimocnemis mollissima

C۴ photosynthesis increases carbon fixation efficiency by separating photosynthesis phases into themesophyll and bundle sheath cells and concentrating CO۲ around Rubisco, reducing photorespiration in aridand hot environments. Consequently, C۴ plants have higher water and nitrogen use efficiency with increasedphotosynthesis rates than C۳ species. As a striking instance of convergent evolution, evolving uniqueanatomical and biochemical features from C۳ progenitors in more than ۶۰ independent lineages ensures thesecharacteristics. Nevertheless, exploring the evolutionary paths and identifying the global regulators of crucialcomponents of C۴ photosynthesis are constrained by the phylogenetic noises in comparative studies. H.mollissima switches C۳ (in cotyledons) to C۴ photosynthesis (in first leaves) during its life cycle. Suchspecies provided an excellent model for studying the C۳ to C۴ transition regulations.Here, we aimed to investigate probable long-distance communication pathways involved in thisdevelopmental transition through transcriptome analysis of hypocotyls. Thus, high-quality RNA wasextracted from hypocotyls before and after the first leaves’ formation and sequenced by Illumina Hi-seq ۲۰۰۰sequencer. After de novo assembly, we identified differentially expressed genes between twodevelopmentally different hypocotyls. They belonged to biosynthesis, transport, and signaling ofphytohormones, various transcription factors (TFs), and plant signaling peptides. Two members of the GRASfamily of TFs, SHORT-ROOT (SHR) and SCARECROW (SCR), and one member of the bZIP TFs, HY۵,were more expressed in hypocotyls after the formation of first leaves. It has already been shown that SHR isa mobile transcription factor and SCR controls Kranz anatomy in maize leaves. Moreover, HY۵ is a masterregulator and a phloem-mediated shoot-to-root signal that adjusts the carbon-nitrogen balance in Arabidopsis.Our findings show the possible signaling pathways involved in the emergence of more advantageous featuresof C۴ photosynthesis.

کلیدواژه ها:

C۴ photosynthesis ، Halimocnemis mollissima ، Long-distance signaling ، RNA sequencing ، Shoot-root coordination