MicroRNAs (miRNAs) have emerged as a class of regulators of gene expression through posttranscriptional degradation or translational repression in living cells. Increasing evidence points to the important relationship between miRNAs and environmental stress responses, but the regulatory mechanisms in plants are poorly understood. Here, we found that Arabidopsis thaliana intronic miR400 was cotranscribed with its host gene (At1g32583) and downregulated by heat treatment. Intriguingly, an alternative splicing (AS) event that occurred in the intron (306 bp) where MIR400 was located was specifically induced by heat stress. A 100 bp fragment was excised, and the remaining 206 bp intron containing MIR400 transcripts was retained in the host gene. The stress-induced AS event thus resulted in greater accumulation of miR400 primary transcripts and a low level of mature miR400. Together, these results provide the direct evidence that AS acts as a regulatory mechanism linking miRNAs and environmental stress in plants.

No abstract

Highlight AtMYB74, a R2R3-MYB gene, is transcriptionally regulated through RdDM for response to salt stress. The accumulation of siRNA targeting to the AtMYB74 promoter region is essential for maintaining AtMYB74 expression.