Physiological and molecular characteristics of two ploidy mutants in Myrica rubra cv. Dongkui

In this study, two ploidy mutant lines of Myrica rubra cv. Dongkui (DK) were identified and named as DB1 and DB2. The floral organ, leaf cell structure, ploidy, and number of chromosomes of the two mutants were investigated. Meanwhile, anthocyanin contents at different developmental stages were analyzed, and the Cy-3-glu contents of DB1 and DB2 at the full ripe stages are significantly higher than that of DK by 27.84 and 23.51%, respectively. Furthermore, 6 RNA libraries at two developmental stages (young fruit stage and full ripe stage) were built for RNA-Seq. By mapping to the reference database, 28 407, 28 043, and 28 683 genes were detected in the young fruit of DB1, DB2, and DK, respectively, while 28 040, 22 256, and 27 351 genes were detected in the full ripe stage, respectively. There were 281 differentially expressed genes between DB1 and DK, with 123 and 158 genes up-regulated and down-regulated, respectively, and 47 differentially expressed genes between DB2 and DK, of which 8 and 39 genes were up-regulated and down-regulated. Using real-time PCR, the expression levels of the eight functional genes at different developmental stages of the fruit were also analyzed. These comprehensive analyses showed that both mutants are different from DK, which is the result of natural doubling of ploidy, thereby generating a pleiotropic effect. As we known, it is the first report to study the relationship between bayberry ploidy alterations and genes involved in regulation of fruit mutations, which will help to identify the morphological and cytological characteristics of M. rubra germplasm, and provide a theoretical basis and technical support for genetic improvement and creation of breeding resources.