RESUMEN
Chickpea (Cicer arietinum) is among the founder crops domesticated in the Fertile Crescent. One of two major forms of chickpea, the so-called kabuli type, has white flowers and light-colored seed coats, properties not known to exist in the wild progenitor. The origin of the kabuli form has been enigmatic. We genotyped a collection of wild and cultivated chickpea genotypes with 538 single nucleotide polymorphisms (SNPs) and examined patterns of molecular diversity relative to geographical sources and market types. In addition, we examined sequence and expression variation in candidate anthocyanin biosynthetic pathway genes. A reduction in genetic diversity and extensive genetic admixture distinguish cultivated chickpea from its wild progenitor species. Among germplasm, the kabuli form is polyphyletic. We identified a basic helix-loop-helix (bHLH) transcription factor at chickpea's B locus that conditions flower and seed colors, orthologous to Mendel's A gene of garden pea, whose loss of function is associated invariantly with the kabuli type of chickpea. From the polyphyletic distribution of the kabuli form in germplasm, an absence of nested variation within the bHLH gene and invariant association of loss of function of bHLH among the kabuli type, we conclude that the kabuli form arose multiple times during the phase of phenotypic diversification after initial domestication of cultivated chickpea.
Asunto(s)
Alelos , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/genética , Cicer/genética , Domesticación , Variación Genética , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/metabolismo , Cicer/anatomía & histología , Productos Agrícolas/genética , Ecotipo , Flores/anatomía & histología , Flores/fisiología , Regulación de la Expresión Génica de las Plantas , Haplotipos/genética , Filogenia , Polimorfismo de Nucleótido Simple/genética , Análisis de Componente Principal , Semillas/anatomía & histologíaRESUMEN
KEY MESSAGE: We report a likely candidate gene, CcTFL1, for determinacy in pigeonpea through candidate gene sequencing analysis, mapping, QTL analysis together with comparative genomics and expression profiling. Pigeonpea (Cajanus cajan) is the sixth most important legume crop grown on ~5 million hectares globally. Determinacy is an agronomically important trait selected during pigeonpea domestication. In the present study, seven genes related to determinacy/flowering pattern in pigeonpea were isolated through a comparative genomics approach. Single nucleotide polymorphism (SNP) analysis of these candidate genes on 142 pigeonpea lines found a strong association of SNPs with the determinacy trait for three of the genes. Subsequently, QTL analysis highlighted one gene, CcTFL1, as a likely candidate for determinacy in pigeonpea since it explained 45-96 % of phenotypic variation for determinacy, 45 % for flowering time and 77 % for plant height. Comparative genomics analysis of CcTFL1 with the soybean (Glycine max) and common bean (Phaseolus vulgaris) genomes at the micro-syntenic level further enhanced our confidence in CcTFL1 as a likely candidate gene. These findings have been validated by expression analysis that showed down regulation of CcTFL1 in a determinate line in comparison to an indeterminate line. Gene-based markers developed in the present study will allow faster manipulation of the determinacy trait in future breeding programs of pigeonpea and will also help in the development of markers for these traits in other related legume species.
