Rong Wu

Cultivated persimmon (Diosspyros kaki Thunb.) is a hexaploid (mostly) or a nonaploid with high heterozygosity, hindering molecular genetic studies on proanthocyanidin (PA) metabolism, which is a major trait for persimmon astringency. Recently, one of its wild diploid relative species, oily persimmon (Diospyros oleifera), has been assembled with a chromosome-level reference. Thus, oily persimmon is now regarded as a model plant for discovering new genes associated with PA metabolism, which is highly accumulated in the fruits of this genus. In our study, we identified genome-wide microRNAs (miRNAs) and their precursor sequence based on the chromosome-scale genome of oily persimmon and the miRNA database of “Eshi 1” according to the sequence alignment and secondary structure accession. The targets were predicted on the psRNATarget software based on the genome CDS database. The size, conservation, diversity, stem-loop hairpin structures, and genome location of miRNA or the precursor sequence were analyzed by bioinformatics tools. The promoter elements of the miRNA genes were predicted on the promoter-2.0 software, which indicated that the abundant cis-acting elements were light responsiveness, promoter, and enhancer regions. The qRT-PCR assay was performed to elucidate the potential expression patterns of precursor miRNA and their targets during fruit development, and one target gene, DkMYB22, of miR2911 was verified to promote the conversion of soluble tannins into insoluble tannins involved in the deastringency in persimmons. Together, this study provides a robust foundation for further functional verification of these miRNAs associated with the natural deastringency process in persimmon, thereby facilitating advancements in persimmon fruit breeding.

MicroRNAs (miRNAs) are endogenous noncoding small RNAs containing 21–24 nucleotides (nt) that regulate gene expression precisely and efficiently at the posttranscriptional level through the negative regulation of target messenger RNA (mRNA) expression, such as translational inhibition or degradation. Likewise, as a controlling element, miRNA itself is regulated by a variety of factors when performing its basic purposes, such as SNP detection, miRNA purging, methylation, and the circadian clock in model crops. In current years, miRNA-mediated controls have been intensely investigated in horticultural plants, leading to the discovery of numerous novel mechanisms that exhibit significantly greater mechanistic complexity and distinctive regulatory properties than those explored in model species. In fruit crops, miRNAs play a crucial role corresponding to various biological, metabolic functions and environmental challenges, including growth, expansion, response to biotic and abiotic stress, signaling of growth hormones, and the regulation of secondary product metabolism. In this study, we appraisal the current improvement of small regulatory RNA research in fruit crops, emphasizing miRNA mechanisms and their correlation with key trait rule. Considering that miRNAs engaged in the regulation of all aspects of fruit tree life activities, we focus here on their biosynthesis, target genes, function and regulatory network, as well as the mechanistic connection among them, to provide a theoretic base and breakthrough for upcoming exploration on miRNAs in fruit plants.