On the hybrid origin of the C₂Salsola divaricata agg. (Amaranthaceae) from C₃ and C₄ parental lineages

Abstract

C2 photosynthesis is characterized by recapturing photorespiratory CO2 by RuBisCO in Kranz-like cells and is therefore physiologically intermediate between C3 and C4 photosynthesis. C2 is either interpreted as an evolutionary precursor of C4 or as the result of hybridization between a C3 and C4 lineage. We compared the expression of photosynthetic traits among populations of the Salsola divaricata agg. (C2) from humid subtropical to arid habitats on the coasts of the Canary Islands and Morocco, and subjected them to salt and drought treatments. We screened for enhanced C4-like expression of traits related to habitat or treatment. We estimated species trees with a transcriptome dataset of Salsoleae and explored patterns of gene tree discordance. With phylogenetic networks and hybridization analyses we tested for hybrid origin of the Salsola divaricata agg. We observed independent variation of photosynthetic traits within and among populations and no clear evidence for selection towards C4-like trait expression in more stressful habitats or treatments. We found reticulation and gene tree incongruencies in the Salsoleae supporting a putative hybrid origin of the Salsola divaricata agg. C2 photosynthesis in the Salsola divaricata agg. combines traits inherited from its C3 and C4 parental lineages and seems well adapted to a wide climatic amplitude.

Exploring the possible role of hybridization in the evolution of photosynthetic pathways in Flaveria (Asteraceae), the prime model of C4 photosynthesis evolution

“…therein). Finally, a C 2 lineage might also be the result of ancient hybridization of a C 3 and a C 4 lineage, as has been suggested for Salsola divaricata , which then might have thrived through the large plasticity of photosynthetic traits inherited from photosynthetically divergent parental lineages (Tefarikis et al, 2021).…”