To understand the mechanism of small non-coding RNAs (miRNA)-mediated development and ripening of mulberry fruits, three small RNA libraries from mulberry fruits at different development stages were constructed, and 159 conserved miRNAs as well as 86 novel miRNAs were successfully identified. Among the miRNAs identified, there were 90 miRNAs which showed differential expression patterns at different stages of fruit development and ripening. The target genes of these differential expressed (DE) miRNAs were involved in growth and development, transcription and regulation of transcription, metabolic processes, and etc. Interestingly, it was found that the expression level of mul-miR477 was increased with fruit ripening, and it can target the antisense lncRNA (Mul-ABCB19AS) of the ATP binding cassette (ABC) transporter B 19 gene (Mul-ABCB19). Our results showed that mul-miR477 can repress the expression of Mul-ABCB19AS and increase the expression of Mul-ABCB19, and it acted as a positive regulator participating anthocyanin accumulation through the regulatory network of mul-miR477-Mul-ABCB19AS-Mul-ABCB19.

To reveal whether the response of mulberry to phytoplasma infection is associated with genome-wide DNA methylation changes, the methylome and transcriptome patterns of mulberry in response to phytoplasma infection were explored. Though the average methylation level of the infected leaves showed no significant difference from that of healthy leaves, there were 1,253 differentially methylated genes (DMGs) and 1,168 differentially expressed genes (DEGs) in the infected leaves, and 51 genes were found simultaneously to be differently methylated and expressed. It was found that the expression of G-type lectin S-receptor-like serine/threonine protein kinase gene (Mu-GsSRK) was increased, but its methylation level was decreased in the pathogen-infected or salicylic acid (SA)-treated leaves. Overexpression of Mu-GsSRK in Arabidopsis and in the hairy roots of mulberry enhanced transgenic plant resistance to the phytoplasma. Moreover, overexpression of Mu-GsSRK enhanced the expressions of pathogenesis-related protein 1, plant defensin, and cytochrome P450 protein CYP82C2 genes in transgenic plants inoculated with pathogens, which may contribute to the enhanced disease resistance against various pathogens. Finally, the DNA methylation dynamic patterns and functions of the differentially expressed and methylated genes were discussed. The results suggested that DNA methylation has important roles in mulberry responses to phytoplasma infection.

MicroRNA (miRNA)作为一种重要的基因表达调控因子,在植物生长发育和响应环境胁迫过程中具有重要的调节功能.本研究克隆了桑树miR482基因(MulmiR482),发现该基因可以表达加工成两种成熟体mul-miR482-5p和mul-miR482-3p,两者在桑树根中均具有较高的表达丰度,而在叶片中的丰度较低.通过拟南芥嫁接试验发现mul-miR482-5p和mul-miR482-3p在植物体内具有长距离运输特性.将MulmiR482基因转入拟南芥,发现其可以在拟南芥中表达并可加工成成熟体,同时发现MulmiR482基因在拟南芥中表达降低了转基因植株对盐胁迫和丁香假单胞菌番茄致病变种DC3000的抗性.上述结果为深入研究桑树mul-miR482的生物功能和其表达调控机制奠定了基础.

To reveal whether the response of mulberry to phytoplasma infection is associated with DNA methylation changes, the methylome and transcriptome patterns of mulberry leaves in response to phytoplasma infection were explored. Though the average methylation level of infected leaves showed no significant difference with that of healthy leaves, there were 1253 differentially methylated genes and 1168 differentially expressed genes found in the infected leaves, and 215 genes were found simultaneously to be differently methylated and expressed. It was found that the expression of G-type lectin S-receptor-like serine/threonine protein kinase gene (Mu-GsSRK) was increased, but its methylation level was decreased in the infected leaves. Moreover, the expression of Mu-GsSRK was increased while its methylation level was reduced in mulberry treated with pathogen and SA. Expression of Mu-GsSRK in Arabidopsis enhanced transgenic plant disease resistance and the expressions of some defense genes when plants were inoculated with pathogens. In addition, the DNA methylation dynamic patterns and the roles of the differentially expressed and methylated genes were discussed. Our results suggested that DNA methylation has important roles in mulberry responses to phytoplasma infection, and the information provided there will facilitate to elucidate the epigenetic mechanisms underlying mulberry responses to phytoplasma infection.