Barley miRNAs and Their Targets Regulation in Response to Heat Stress at the Early Stage of Development

MiRNAs are key regulators of gene expression, controlling plant development and response to environmental stresses. In this work, we studied the global dynamics of the accumulation of conserved and identified novel barley miRNAs at an early stage of plant development during heat stress (1 h, 3 h and 6 h of heat stress). The majority of miRNAs respond to heat stress after 3 h and 6 h of heat stress duration (124 and 155, respectively). The comparison of heat-induced changes in mature miRNA accumulation to their cognate precursor levels allowed us to indicate a smaller group of miRNAs that are controlled at the transcriptional level and a larger group that is controlled post-transcriptionally in response to heat stress. For miRNAs with significant accumulation changes during heat treatment, target mRNAs were identified. Moreover, novel targets have been experimentally assigned for selected miRNAs. mRNA of the effector protein of miRNA activity, AGO1B, was found to be downregulated by increased miR168 during heat stress. Importantly, the miRNA/mRNA target module miR399c/PHO2, responsible for phosphorus uptake, exhibits dynamic changes under heat stress conditions, suggesting adaptation of plant development to stress conditions. This study provides new data for developing miRNA and their mRNA target-based strategies in barley breeding in response to heat stress.