Small RNAs With a Big Impact on Horticultural Traits

The role of protein-encoding genes in determining phenotype is well established, whereas the impact of small RNAs in regulating horticultural traits is being gradually recognized. Small RNAs are small noncoding RNAs of 20–24-nt, which regulate target genes by post-transcriptional regulation or de-novo DNA methylation. In plants, small RNAs are classified into the following two major categories, microRNA (miRNA) and short interfering RNA (siRNA). Most small RNA research focuses on model plants (e.g. Arabidopsis, tomato and rice), and has identified the function of small RNAs on plant development (e.g. meristem organization, leaf development, flower organ identity and transition to flowering). Recently, small RNA sequencing has been applied to study gene regulation in horticultural crops. Plant specific small RNA (miRNAs and phasiRNAs) families have similar function across model plants to horticultural crops. In addition, most plants have unique nonconserved small RNAs, which might affect specific traits. This review focuses on small RNA biogenesis, function prediction and the roles of small RNAs in horticultural traits (e.g. flowering, fruit quality, abiotic and biotic stress), and summarizes small RNA information for future horticultural crop research and breeding.