Phylogenetic analysis of tribe Salsoleae (Chenopodiaceae) based on ribosomal ITS sequences: Implications for the evolution of photosynthesis types

Diversity in photosynthetic pathways in the angiosperm family Chenopodiacea e is expressed in both biochemical and anatomical characters. To understand the evolution of photosynthetic diversity, we reconstructed the phylogeny of representative species of tribe Salsoleae of subfamily Salsoloideae, a g roup that exhibits in microcosm the patterns of photosynthetic variation pr esent in the family as a whole, and examined the distribution of photosynth etic characters on the resulting phylogenetic tree. Phylogenetic relationsh ips were inferred from parsimony analysis of nucleotide sequences of the in ternal transcribed spacer regions (ITS) of the 18S-26S nuclear ribosomal DN A of 34 species of Salsola and related genera (Halothamnus, Climacoptera, G irgensohnia, Halocharis, and Haloxylon) and representative outgroups from t ribes Camphorosmeae (Camphorosma lessingii, Kochia prostrata, and K. scopar ia) and Atripliceae (Atriplex spongiosa). A highly resolved strict consensu s tree largely agrees with photosynthetic type and anatomy of leaves and co tyledons. The sequence data provide strong support for the origin and evolu tion of two main lineages of plants in tribe Salsoleae, with NAD-ME and NAD P-ME C-4 photosynthesis, respectively. These groups have different C-4 phot osynthetic types in leaves and different structural and photosynthetic char acteristics in cotyledons. Phylogenetic relationships inferred from ITS seq uences generally agree with classifications based on morphological data, bu t deviations from the existing taxonomy were also observed. The NAD-ME C-4 lineage contains species classified in sections Caroxylon, Malpigipila, Car diandra, Belanthera, and Coccosalsola, and the NADP-ME lineage comprises sp ecies from sections Coccosalsola and Salsola. Reconstruction of photosynthe tic characters on the ITS phylogeny indicates separate NAD-ME and NADP-ME l ineages and suggests two reversions to C-3 photosynthesis. Reconstruction o f geographic distributions suggests Salsoleae originated and diversified in central Asia and subsequently dispersed to Africa, Europe, and Mongolia. I nferred patterns and processes of photosynthetic evolution in Salsoleae sho uld further our understanding of biochemical and anatomical evolution in Ch enopodiaceae as a whole.