Insights into Regulation of C2 and C4 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.

Automated summary

This study conducted RNA-Seq and comparative transcriptome analysis on three species from Camphorosmeae with different photosynthetic types. The results showed significant upregulation of core genes encoding the C-4 cycle in B. prostrata, while two C-4 transporters were upregulated in Sed. sedoides. Furthermore, analysis of transcription factors revealed differences in expression among species.