A Class II KNOX Gene, KNAT7-1, Regulates Physical Seed Dormancy in Mungbean [Vigna radiata (L.) Wilczek]

Abstract

Seed dormancy in wild mungbean (<i>Vigna radiata</i> var. <i>sublobata</i>) may be useful for the breeding of cultivated mungbean (var. <i>radiata</i>) with pre-harvest sprouting resistance. Previous studies have identified two major quantitative trait loci (QTLs) for seed dormancy, <i>HsA</i> and <i>Sdwa5.1.1</i>+, in wild mungbean that are possibly having the same locus or linked. However, these QTLs have not been confirmed/verified and a molecular basis of seed dormancy in mungbean is not yet known. In this study, we aimed to finely map the <i>Sdwa5.1.1</i>+ and identify candidate gene(s) for this locus. Microscopic observations revealed that wild mungbean "ACC41" seeds had a palisade cuticle layer, while cultivated mungbean "Kamphaeng Saen 2" (KPS2) seeds lacked this layer. Fine mapping using an F₂ population developed from a cross between ACC41 and KPS2 revealed two linked QTLs, <i>Sdwa5.1.1</i>+ and <i>Sdwa5.1.2</i>+, controlling seed dormancy. The <i>Sdwa5.1.1</i>+ was confirmed in an F_2:3 population derived from the same cross and mapped to a 3.298-Kb region containing only one gene <i>LOC106767068</i>, designated as <i>VrKNAT7-1</i>, which encodes the transcription factor KNOTTED ARABIDOPSIS THALIANA7 (KNAT7), a class II KNOTTED1-LIKE HOMEOBOX (KNOX II) protein. <i>VrKNAX7</i> sequence alignment between ACC41 and KPS2 revealed several polymorphisms in the coding, untranslated, and promoter regions. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of <i>VrKNAT7-1</i> and <i>VrCYP86A</i>, a putative downstream regulation of <i>VrKNAT7-1</i>, in the seed coat of ACC41 is statistically much higher than that of KPS2. Altogether, these results indicate that <i>VrKNAT7-1</i> controls physical seed dormancy in the wild mungbean ACC41.