A 294 kb deletion causes reduced leaflet size and biomass in pigeonpea.

Key message: BSA-seq and fine mapping revealed a 294 kb deletion on chromosome 9 regulating leaflet size and biomass in pigeonpea. Leaf size critically influences photosynthetic capacity, impacting organic matter production and biomass yield. This study reports the identification and characterization of a small leaflet mutant (sl1) in pigeonpea (Cajanus cajan) generated via aerial mutagenesis. Compared to the wild-type Qiongzhong, sl1 displayed significantly reduced leaf area, plant height, stem diameter, and biomass, characteristic of a dwarf phenotype. Genetic analysis confirmed a single recessive locus controlling the sl1 phenotype. Bulked segregant analysis sequencing (BSA-seq) and fine mapping identified the causal mutation as a 294 kb deletion encompassing 21 genes on chromosome 9. Transcriptomic analysis identified 1,039 differentially expressed genes (DEGs), indicating disruptions in, among others, plant hormone signaling pathways. Analysis of 28 target plant hormone metabolites revealed significant shifts in sl1 mutant compared to wild-type, including increased levels of strigolactone, methyl indole-3-acetate, and trans-zeatin-riboside, and decreases in gibberellin A3, N6-isopentenyladenine, and methyl jasmonate. Cytological analysis revealed a decreased cell number in sl1 leaves, contributing to the reduced leaflet size. Three candidate genes, CC09g01700, CC09g01705, and CC09g01707, within the deleted region were prioritized based on their altered expression patterns and their putative roles in leaf development. These findings elucidate the genetic regulation of leaf morphology and biomass in pigeonpea, offering potential targets for marker-assisted selection to enhance pigeonpea yield.