Identification and Fine Mapping of a Mutant <i>pv‐nts</i> Gene Responsible for Dwarf and Thin Stem of Snap Bean (<scp><i>Phaseolus vulgaris</i></scp> L.)

ABSTRACT Plant height is one of the most important traits in the breeding of snap bean, which determines the planting density and the resistance to failure, which in turn affects its yield and quality. Therefore, studying the molecular mechanism of plant height in snap bean is an important measure to realize the improvement of snap bean. We obtained a dwarf, thin‐stemmed mutant nts (normal to slim) from a dwarf variety of snap bean A18 via 60 CO‐γ‐ray treatment. We conducted phenotypic observations, endogenous hormone content measurements and genetic analyses of the dwarfing thin‐stemmed mutant nts and explored gene localization and candidate gene screening for the mutant trait in snap bean. Compared with wild‐type A18, nts mutant exhibited various abnormal phenotypes such as dwarfing, reduced branching, thinner top stem, reduced plant width, reduced number of leaf area and thousand grain weight and increased content of hormones such as indole‐3‐acetic acid (IAA) in the top stem. Genetic analysis indicated that the mutant trait was controlled by a single recessive nuclear gene, and the mutant gene was named pv‐nts . pv‐nts was localized to a 361.1‐kb segment on chromosome 8 as revealed by bovine serum albumin (BSA) hybrid pool sequencing and simple sequence repeat (SSR) molecular markers. Phvul.008G106300 (encoding LAX2 protein) was identified as a candidate gene corresponding to pv‐nts via gene function annotation. Phvul.008G106300 was significantly upregulated in nts mutant compared with wild‐type A18, which was consistent with the results of endogenous IAA levels. Sequence analysis showed that the Phvul.008G106300 gene in nts had a base mutation that altered the protein structure, thus causing the dwarfed, thin‐stemmed phenotype of cauliflower. Taken together, these results contribute to a better understanding of the genetic basis of dwarfing traits in snap bean.