Identification of Quantitative Trait Loci (QTLs) and candidate genes for trichome development in Brassica villosa using genetic, genomic, and transcriptomic approaches.

Brassica villosa is characterized by its dense hairiness and high resistance against the fungal pathogen Sclerotinia sclerotiorum. Information on the genetic and molecular mechanisms governing trichome development in B. villosa is rare. Here, we analyzed an F₂ population, derived from a cross between B. villosa and the glabrous B. oleracea by QTL mapping and transcriptomic analyses. As a result, the phenotyping of 171 F₂ progenies revealed a wide range of variation in trichome development. Subsequent genotyping with the 15-k Illumina SNP array resulted in a genetic map with 970 markers and a total length of 812 cM. Four QTLs were identified, which explained phenotypic variation from 3.2% to 40.3%. Interestingly, one of these was partially co-localized with the major QTL for Sclerotinia-resistance previously detected in the same F₂ population. However, only a moderate correlation between trichomes and Sclerotinia-resistance was observed. In total, 133 differentially expressed genes (DEGs) associated with trichome development were identified, from which only BoTRY, an orthologue of Arabidopsis TRY encoding a MYB transcription factor negatively regulating trichome development, was located within the major QTL. Expression of BoTRY was tissue-specific and highly variable between the hairy and glabrous species, suggesting that BoTRY may also act as a master-switch regulator of trichome development in B. villosa. This study provides valuable data for further understanding the genetic architecture of trichome development and identifying related genes and mechanisms in Brassica species. Molecular markers can be developed to facilitate the introgression and selection of this trait in oilseed rape breeding.