Insights into Regulation of C(2) and C(4) Photosynthesis in Amaranthaceae/Chenopodiaceae Using RNA-Seq

Amaranthaceae (incl. Chenopodiaceae) shows an immense diversity of C(4) syndromes. More than 15 independent origins of C(4) photosynthesis, and the largest number of C(4) species in eudicots signify the importance of this angiosperm lineage in C(4) evolution. Here, we conduct RNA-Seq followed by comparative transcriptome analysis of three species from Camphorosmeae representing related clades with different photosynthetic types: Threlkeldia diffusa (C(3)), Sedobassia sedoides (C(2)), and Bassia prostrata (C(4)). Results show that B. prostrata belongs to the NADP-ME type and core genes encoding for C(4) cycle are significantly upregulated when compared with Sed. sedoides and T. diffusa. Sedobassia sedoides and B. prostrata share a number of upregulated C(4)-related genes; however, two C(4) transporters (DIT and TPT) are found significantly upregulated only in Sed. sedoides. Combined analysis of transcription factors (TFs) of the closely related lineages (Camphorosmeae and Salsoleae) revealed that no C(3)-specific TFs are higher in C(2) species compared with C(4) species; instead, the C(2) species show their own set of upregulated TFs. Taken together, our study indicates that the hypothesis of the C(2) photosynthesis as a proxy towards C(4) photosynthesis is questionable in Sed. sedoides and more in favour of an independent evolutionary stable state.