Temperature-dependent plants microRNA processing pathway

RÉ DELFINA; LANG PATRICIA; WEIGEL DETLEF; MANAVELLA PABLO

Lugano

Congreso; HFSP 2014 Awardees Meeting; 2014

HFSP

MicroRNAs (miRNAs) are small, ~21-nucleotide, RNA molecules that are critical for the normal development of multicellular organisms. The key feature that makes miRNAs fundamental for plant homeostasis is their evolutionary preference to silence transcription factors. These small regulatory molecules are produced from primary miRNA transcripts by a single nuclear enzyme, DICER-LIKE 1 (DCL1). The accurate excision of the miRNA duplexes relies on the interaction of DCL1, SERRATE (SE), and HYPONASTIC LEAVES1 (HYL1). The miRNA processing complex works as a molecular ruler recognizing the correct position in the miRNA primary transcript releasing the mature miRNA. Some features of the secondary structure of miRNA precursors are key for the correct positioning of DCL1 during processing. In the absence of HYL1 or SE, DCL1 is unable to recognize the correct cleavage site and end up producing less or aberrant miRNAs leading to severe morphological phenotypes. Growing hyl1 and serrate mutants at low temperatures abolish their typical morphological defects and restore their fertility. Dissection of mutant and wild type siliques, grown at 23 °C and 16 °C, has shown a reduction in the embryonic abortion from ~85% to ~15%. We found that the high embryonic lethality rate observed in the mutants at 23 °C is a consequence of a regulatory disequilibrium cause by the reduction in the production of miRNAs. Measurements of endogenous miRNAs by northern blot showed a restoration of the miRNA production at low temperatures, which explains the concomitant recovery on the fertility. In silico analysis suggested that the secondary structure adopted by a miRNA precursors at low temperature is the cause of such effect. Our observations suggest the existence of a HYL1/SE independent biogenesis pathway where DCL1 can act without assistance in specific conditions.