Diversity of PsSym29 and PsNRLK1 genes in the VIR germplasm collection of pea (Pisum sativum L.)

BACKGROUND: N.I. Vavilov Institute of Plant Genetic Resources (VIR) (Saint Petersburg, Russia) maintains a large collection of pea (Pisum sativum L.). Earlier, several growth and yield parameters were recorded for plants of 99 accessions grown under inoculation with nodule bacteria and arbuscular mycorrhizal fungi. 
MATERIALS AND METHODS: Polymorphism of genes encoding symbiotic receptor kinase PsSym29 [participating in the autoregulation of nodulation (AON) system] and closely related receptor kinase PsNRLK1 (with yet unknown function in symbiosis) was assessed in 99 pea genotypes from the VIR collection. Nucleotide diversity, Tajimas D, and Fay and Wus H statistics were calculated using DNAsp 5.0 software. The significance of associations of allelic state of the sequenced genes with the growth and yield parameters was tested by two-way ANOVA followed by FDR correction and by regression analysis. 
RESULTS: Nucleotide diversity and the ratio of synonymous to non-synonymous substitutions was greater in PsNRLK1 as compared to PsSym29. The analysis of Fay and Wus H in sliding window revealed signatures of positive selection in one site of PsSym29 and in three sites of PsNRLK1 gene sequences located in 1st exons encoding LRR (leucine rich repeat) domains. No significant associations of allelic state of neither PsSym29 nor PsNRLK1 genes was found with plant growth and yield parameters. 
CONCLUSIONS: The sequences of both PsSym29 and PsNRLK1 genes undergo positive selection, but the conditions in which specific allelic states of the genes become adaptive are to be elucidated in future.