Histone lysine methyltransferases Bna SDG 8.A and Bna SDG 8.C are involved in the floral transition in Brassica napus

Summary Although increasing experimental evidence demonstrates that histone methylations play important roles in Arabidopsis plant growth and development, little information is available regarding Brassica napus . In this study, we characterized two genes encoding homologues of the Arabidopsis histone 3 lysine 36 (H3K36) methyltransferase SDG 8, namely, Bna SDG 8.A and Bna SDG 8.C . Although no duplication of SDG 8 homologous genes had been previously reported to occur during the evolution of any sequenced species, a domain‐duplication was uncovered in Bna SDG 8.C . This duplication led to the identification of a previously unknown NNH domain in the SDG 8 homologues, providing a useful reference for future studies and revealing the finer mechanism of SDG 8 function. One NNH domain is present in Bna SDG 8.A, while two adjacent NNH domains are present in Bna SDG 8.C. Reverse transcriptase‐quantitative polymerase chain reaction analysis revealed similar patterns but with varied levels of expression of Bna SDG 8.A/C in different plant organs/tissues. To directly investigate their function, Bna SDG 8.A / C cDNA was ectopically expressed to complement the Arabidopsis mutant. We observed that the expression of either Bna SDG 8.A or Bna SDG 8.C could rescue the Arabidopsis sdg8 mutant to the wild‐type phenotype. Using RNA i and CRISPR /Cas9‐mediated gene editing, we obtained Bna SDG 8.A / C knockdown and knockout mutants with the early flowering phenotype as compared with the control. Further analysis of two types of the mutants revealed that Bna SDG 8.A/C are required for H3K36 m2/3 deposition and prevent the floral transition of B. napus by directly enhancing the H3K36 m2/3 levels at the Bna FLC chromatin loci. This observation on the floral transition by epigenetic modification in B. napus provides useful information for breeding early‐flowering varieties.