Identification of a unique allele BrTRI1 regulating the trichomeless trait of Chinese cabbage (Brassica rapa L. ssp. pekinensis)

The trichome is a specialized structure developed from the epidermal cells of plants. It serves as a protective tissue covering the surface of plants, playing a crucial role in shielding plants against biotic and abiotic stresses. The trichomeless trait is a necessary quality trait of seedling Chinese cabbage, contributing to the enrichment of Chinese cabbage germplasm resources. This study analyzed the trichomeless mutant Y358-10 and identified the trichomeless trait as being controlled by the recessive gene BrTRI1. Through BSA-seq (Bulked sergeant analysis) and KASP (Kompetitive allele -specific PCR) techniques, the BrTRI1 gene was located on chromosome A06 at 24.91-24.95 Mb. Functional annotation analysis revealed that BraA06g038610.3.5C is a homologous gene of Arabidopsis AtGL1 and induces trichome formation, which may be a candidate gene for BrTRI1. Sequence analysis revealed a 108 bp insertion in the promoter region and transposable element (TE) insertion in the third exon of BraA06g038610.3.5C, differing from the previously published mutation. The InDel markers BrTRI1-PI and BrTRI1-TE were developed and validated in the F2 population and 342 DH (Double haploid) and high inbred lines. We identified all reported variants of BrTRI1 and BrTTG1 among 342 DH and high inbred lines, which covered the widest variation range and the most germplasm resources. The results demonstrated that only the identical source Y358-10 and Y358P1 concomitantly conformed to BrTRI1-PI and BrTRI1-TE. RNA-seq and qRTPCR analyses indicated that variations in BraA06g038610.3.5C and the differential expression of other genes involved in trichome development in Y358-10 resulted in the inhibition of trichome formation. This provides a new perspective for studying the molecular mechanism of Chinese cabbage trichome formation and genetic improvement.