Change in ambient temperature is one of the most variable environmental signals experienced by plants on a daily basis, and microRNAs (miRNAs) are particularly important for temperature change responses. In this study, Pablo Manavella and colleagues show that plant miRNA biogenesis becomes more robust at low temperatures. The authors examine mutants for miRNA biogenesis co-factor-coding genes in Arabidopsis, such as HYPONASTIC LEAVES 1 (HYL1). hyl1 mutants normally display developmental defects when grown in standard conditions, but show an overall attenuated phenotype when cultivated at lower temperatures. The authors use small RNA gel blots and sequencing to show loss of miRNA accumulation in hyl1 mutants in ambient temperatures. However, some miRNAs accumulate in hyl1 mutants cultivated at low temperatures, indicating a temperature-dependent, but HYL-independent, miRNA biogenesis mechanism. Importantly, the researchers correlate primary miRNA transcripts with secondary structure, revealing that high-energy pairings (G-C rich) are most sensitive to loss of HYL1-dependent biosynthesis. Finally, they show that a decrease in ambient temperature improves miRNA-processing precision. This study highlights flexibility within the miRNA biogenesis pathway and the importance of temperature for primary miRNA processing, which could be an evolutionary adaptation to changing climates.
