In Arabidopsis thaliana, the dependence of some miRNA on biogenesis cofactors for its production, such as HYL1, is conditioned by the plant growth temperature. The levels of some miRNA are low in hyl1 mutants grown at 22ºC, but are restored under 16ºC in the same mutant plants.

In regular growth chamber conditions (22-23 °C, long-day photoperiod) miRNAs are produced by the catalytic action of the type II ribonuclease DICER LIKE 1 (DCL1). During this reaction HYPONASTIC LEAVES 1 (HYL1) and SERRATE (SE) are necessary for the accurate excision of the miRNAs from their long and complex primary transcripts. Once produced, miRNAs are methylated by HEN1 and loaded into ARGONAUTE 1 (AGO1) to carry out their regulatory functions. Mutations in the genes that encode these proteins have severe consequences for miRNAs production/stability, plant homeostasis and phenotypic traits. In our lab, we observed that plants with mutations in DCL1-cofactors HYL1 and SE showed an attenuated phenotype and increased fertility, as measured by seed production, embryonic abortion and pollen viability, when grown at 16 ºC, compared to 23 ºC grown plants. These phenomena were not evidenced in mutants affecting proteins downstream of the core miRNA-biogenesis, suggesting that such effects caused by lowering the temperature are produced during the initial steps of miRNA biogenesis. We found that there are temperature responsive-, not responsive- and HYL1 independent miRNAs, which we categorized with a small RNA sequencing of Col-0 and hyl1-2 plants grown at 23 °C and 16 °C.