A single amino acid residue substitution in BraA04g017190.3C, a histone methyltransferase, results in premature bolting in Chinese cabbage (Brassica rapa L. ssp. Pekinensis)

Abstract

Background Flowering is an important inflection point in the transformation from vegetative to reproductive growth, and premature bolting severely decreases crop yield and quality. Results In this study, a stable early-bolting mutant, ebm3, was identified in an ethyl methanesulfonate (EMS)-mutagenized population of a Chinese cabbage doubled haploid (DH) line ‘FT’. Compared with ‘FT’, ebm3 showed early bolting under natural cultivation in autumn, and curled leaves. Genetic analysis showed that the early-bolting phenotype was controlled by a single recessive nuclear gene. Modified MutMap sequencing, genotyping analyses and allelism test provide strong evidence that BrEBM3 (BraA04g017190.3 C), encoding the histone methyltransferase CURLY LEAF (CLF), was the strongly candidate gene of the emb3. A C to T base substitution in the 14th exon of BrEBM3 resulted in an amino acid change (S to F) and the early-bolting phenotype of emb3. The mutation occurred in the SET domain (Suppressor of protein-effect variegation 3–9, Enhancer-of-zeste, Trithorax), which catalyzes site- and state-specific lysine methylation in histones. Tissue-specific expression analysis showed that BrEBM3 was highly expressed in the flower and bud. Promoter activity assay confirmed that BrEBM3 promoter was active in inflorescences. Subcellular localization analysis revealed that BrEBM3 localized in the nucleus. Transcriptomic studies supported that BrEBM3 mutation might repress H3K27me3 deposition and activate expression of the AGAMOUS (AG) and AGAMOUS-like (AGL) loci, resulting in early flowering. Conclusions Our study revealed that an EMS-induced early-bolting mutant ebm3 in Chinese cabbage was caused by a nonsynonymous mutation in BraA04g017190.3 C, encoding the histone methyltransferase CLF. These results improve our knowledge of the genetic and genomic resources of bolting and flowering, and may be beneficial to the genetic improvement of Chinese cabbage.

Brassica rapa CURLY LEAF is a major H3K27 methyltransferase regulating flowering time

“…In addition, we found that braA.clf-1 displayed early flowering, which is consistent with recent reports indicating that mutations in the Chinese cabbage ( B. rapa ssp. pekkinensis ) CLF homolog promotes premature bolting (Huang et al 2020 ; Tan et al 2021 ). However, the early-flowering phenotype of braA.clf-1 was not as conspicuous as the Chinese cabbage and A. thaliana mutant alleles, due to R-o-18 being already an early-flowering B. rapa variety.…”

Transcriptomic and epigenomic analyses revealed that polycomb repressive complex 2 regulates not only developmental but also stress responsive metabolism in Brassica rapa

“…pekinensis , named as ebm1 and ebm3 ) and yellow sarson inbred line R-o-18 ( B. rapa ssp. trilocularis , named braA.clf-1 ; Payá-Milans et al., 2019 ; Huang et al., 2020 ; Tan et al., 2021 ). braA.clf plants exhibited pleiotropic developmental changes which were resulted from the de-repression of developmental genes via the reduction of enrichment of H3K27me3 ( Payá-Milans et al., 2019 ).…”