A rare stop-gain SNP mutation in BrGL2 causes aborted trichome development in Chinese cabbage (Brassica rapa L. ssp. pekinensis).

Abstract

Key message: A rare stop-gain SNP mutation in BrGL2 confers short hair phenotype of Chinese cabbage via bulked-segregant analysis sequencing, fine-mapping and gene silencing analysis. Trichomes negatively affect the quality of Chinese cabbage, a leafy vegetable crop in the family Brassicaceae. The short hair trait is caused by abnormal trichome development. In this study, the BraA07g025490.3C gene was identified as a candidate gene for the short hair trait in Chinese cabbage by BSA-seq and fine-mapping analyses. It was subsequently named BrGL2 because of its strong homology to AtGL2 (At1g79840). Sequence analysis indicated that a C to G single-nucleotide polymorphism (SNP) mutation in the sixth exon of BrGL2 produced a premature stop codon in the HCW (short hair) line, resulting in a loss-of-function mutation of BrGL2. This stop-gain SNP mutation was found exclusively in the HCW line, and not in 524 diverse B. rapa accessions. Further analysis by virus-induced gene silencing showed that the knock-down of BrGL2 in HN19-G lines (wild-type hair) reduced the size of leaf trichomes. BrGL2 affected trichome development probably by impacting the expression of downstream transcription factor genes and cell wall-related genes, as determined by comparative transcriptome analyses of wild type and short hair lines. On the basis of the identification and verification of the key stop-gain SNP mutation in BrGL2 resulting in aborted trichome development in Chinese cabbage, we propose a model for trichome development.