Positive selection of Kranz and non-Kranz C4phosphoenolpyruvate carboxylase amino acids in Suaedoideae (Chenopodiaceae)

• Published in: Journal of experimental botany Vol. 65; no. 13; pp. 3595 - 3607
• Main Authors: Rosnow, Josh J., Edwards, Gerald E., Roalson, Eric H.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.01.2014
• Subjects: Amino acids; Anatomy; C4 photosynthesis; Codons; Corn; Enzymes; Kinetics; Phylogenetics; Plant biochemistry; Positive selection; RESEARCH PAPER
• ISSN: 0022-0957; 1460-2431

In subfamily Suaedoideae, four independent gains of C 4 photosynthesis are proposed, which includes two parallel origins of Kranz anatomy (sections Salsina and Schoberia) and two independent origins of single-cell C 4 anatomy (Bienertia and Suaeda aralocaspica). Additional phylogenetic support for this hypothesis was generated from sequence data of the C-terminal portion of the phosphoenolpyruvate carboxylase (PEPC) gene used in C 4 photosynthesis (ppc-1) in combination with previous sequence data. ppc-1 sequence was generated for 20 species in Suaedoideae and two outgroup Salsola species that included all types of C 4 anatomies as well as two types of C 3 anatomies. A branch-site test for positively selected codons was performed using the software package PAML. From labelling of the four branches where C 4 is hypothesized to have developed (foreground branches), residue 733 (maize numbering) was identified to be under positive selection with a posterior probability >0.99 and residue 868 at the >0.95 interval using Bayes empirical Bayes (BEB). When labelling all the branches within C 4 clades, the branch-site test identified 13 codons to be under selection with a posterior probability >0.95 by BEB; this is discussed considering current information on functional residues. The signature C 4 substitution of an alanine for a serine at position 780 in the C-terminal end (which is considered a major determinant of affinity for PEP) was only found in four of the C 4 species sampled, while eight of the C 4 species and all the C 3 species have an alanine residue; indicating that this substitution is not a requirement for C 4 function.