Structural variation of GL1 gene determines the trichome formation in Brassica juncea

A 448 kb region on chromosome B02 was delimited to be associated with trichome trait in Brassica juncea, in which the BjuVB02G54610 gene with a structural variation of 3 kb structure variation (SV) encoding a MYB transcription factor was predicted as the possible candidate gene. Mustards (Brassica juncea) are allopolyploid crops in the worldwide, and trichomes are essential quality attributes that significantly influence its taste and palpability in vegetable-use cultivars. As important accessory tissues from specialized epidermal cells, trichomes also play an important role in mitigating biotic and abiotic stresses. In this study, we constructed a F2 segregating population using YJ27 with intensive trichome leaves and 03B0307 with glabrous leaves as parents. By bulked segregant analysis (BSA-seq), we obtained a 2.1 Mb candidate region on B02 chromosome associated with the trichome or glabrous trait formation. Then, we used 13 Kompetitive Allele Specific PCR (KASP) markers for fine mapping and finally narrowed down the candidate region to about 448 kb in length. Interestingly, among the region, there was a 3 kb sequence deletion that located on the BjuVB02G54610 gene in the F2 individuals with trichome leaves. Genotyping results of F2 populations confirmed this deletion (R2 = 81.44%) as a major QTL. Natural population re-sequencing analysis and genotyping results further validated the key role of the 3 kb structure variation (SV) of insertion/deletion type in trichome development in B. juncea. Our findings provide important information on the formation of trichomes and potential target gene for breeding vegetable mustards.