The novel gene BrMYB2, located on chromosome A07, with a short intron 1 controls the purple-head trait of Chinese cabbage (Brassica rapa L.)

Abstract

Anthocyanins are important secondary metabolites in plants, but information on anthocyanin biosynthesis mechanisms in Chinese cabbage is limited. The new purple head Chinese cabbage cultivar 11S91 was analyzed, and an R2R3-MYB regulatory gene <i>BrMYB2</i>, located on chromosome A07, controlling the dominant purple-head trait was isolated. High expression of <i>BrMYB2</i> generated a large accumulation of anthocyanins in 11S91, accompanied by highly upregulated <i>BrTT8</i>, <i>BrF3</i>'<i>H</i>, <i>BrDFR1</i>, <i>BrANS1</i>, <i>BrUGT</i>s, <i>BrAT</i>s, and <i>BrGST</i>s. 11S91 inherited the purple locus from purple trait donor 95T2-5, and they shared consensus CDSs and gDNAs with those of <i>BrMYB2</i> (<i>cBrMYB2</i> and <i>gBrMYB2</i>). Two SNPs in <i>cBrMYB2</i> in 11S91 did not cause loss of function; in addition to several SNPs at both ends of intron 1, a large deletion had occurred in intron 1 of <i>gBrMYB2</i> in 11S91. Genetic transformation of <i>Arabidopsis</i> showed that <i>gBrMYB2</i> overexpression lines presented deeper purple color and higher expression than did the c<i>BrMYB2</i> and c<i>Brmyb2</i> lines, whereas <i>gBrmyb2</i> with a long intron 1 did not cause the purple phenotype. We first show that <i>BrMYB2</i> promotes anthocyanin biosynthesis under the control of the short intron 1 of g<i>BrMYB2</i> in purple head Chinese cabbage, and <i>gBrmyb2</i> with a long intron 1 represses anthocyanin production in white head Chinese cabbage. This evidence provides a new understanding of anthocyanin biosynthesis and purple germplasm generation in <i>Brassica</i> vegetables.