Small RNAs, emerging regulators critical for the development of horticultural traits

Small RNAs(sRNAs)have been recently recognized as key genetic and epigenetic regulators in various organisms,ranging from the modification of DNA and histone methylations to the modulation of the abundance of coding or non-coding RNAs.In plants,major regulatory sRNAs are classified as respective microRNA(miRNA)and small interfering RNA(siRNA)species,with the former primarily engaging in posttranscriptional regulation while the latter in transcriptional one.Many of these characterized sRNAs are involved in regulation of diverse biological programs,processes,and pathways in response to developmental cues,environmental signals/stresses,pathogen infection,and pest attacks.Recently,sRNAs-mediated regulations have also been extensively investigated in horticultural plants,with many novel mechanisms unveiled,which display far more mechanistic complexity and unique regulatory features compared to those studied in model species.Here,we review the recent progress of sRNA research in horticultural plants,with emphasis on mechanistic aspects as well as their relevance to trait regulation.Given that major and pioneered sRNA research has been carried out in the model and other plants,we also discuss ongoing sRNA research on these plants.Because miRNAs and phased siRNAs(phasiRNAs)are the most studied sRNA regulators,this review focuses on their biogenesis,conservation,function,and targeted genes and traits as well as the mechanistic relation between them,aiming at providing readers comprehensive information instrumental for future sRNA research in horticulture crops.

Thermal-responsive genetic and epigenetic regulation of DAM cluster controlling dormancy and chilling requirement in peach floral buds

The Dormancy-associated MADS-box(DAM)gene cluster in peach serves as a key regulatory hub on which the seasonal temperatures act and orchestrate dormancy onset and exit,chilling response and floral bud developmental pace.Yet,how different temperature regimes interact with and regulate the six linked DAM genes remains unclear.Here,we demonstrate that chilling downregulates DAM1 and DAM3–6 in dormant floral buds with distinct patterns and identify DAM4 as the most abundantly expressed one.We reveal multiple epigenetic events,with tri-methyl histone H3 lysine 27(H3K27me3)induced by chilling specifically in DAM1 and DAM5,a 21-nt sRNA in DAM3 and a ncRNA induced in DAM4.Such induction is inversely correlated with downregulation of their cognate DAMs.We also show that the six DAMs were hypermethylated,associating with the production of 24-nt sRNAs.Hence,the chilling-responsive dynamic of the different epigenetic elements and their interactions likely define distinct expression abundance and downregulation pattern of each DAM.We further show that the expression of the five DAMs remains steadily unchanged or continuously downregulated at the ensuing warm temperature after chilling,and this state of regulation correlates with robust increase of sRNA expression,H3K27me3 and CHH methylation,which is particularly pronounced in DAM4.Such robust increase of repressive epigenetic marks may irreversibly reinforce the chillingimposed repression of DAMs to ensure flower-developmental programming free from any residual DAM inhibition.Taken together,we reveal novel information about genetic and epigenetic regulation of the DAM cluster in peach,which will be of fundamental significance in understanding of the regulatory mechanisms underlying chilling requirement and dormancy release,and of practical application for improvement of plasticity of flower time and bud break in fruit trees to adapt changing climates.