HWS and its role as a co-factor involved in miRNA biogenesis.

GAGLIARDI, DELFINA; CAMBIAGNO, DAMIAN A.; MANAVELLA PABLO A.

Congreso; XXXIII ARGENTINIAN MEETING OF PLANT PHYSIOLOGY; 2021

MiRNAs are 21-24 nt molecules that regulatemost developmental and stress response pathways in plants. Since HASTY (HST) was first identified, it was proposedto export plant miRNAs from the nucleus to the cytoplasm, a premise based on its homology with human EXPORTIN 5. Recently, it has been shown that HST interacts with MED37 subunits and acts as a scaffold to recruit DCL1to MIRNA loci, promoting the transcription and processing of pri-miRNAs,and laterthe non-cell-autonomous function ofmiRNAs,rather than the direct export of processed miRNAs from the nucleus. Complementary to these studies, and aimingto elucidate the role of HST, we performed a suppressor screening onhst-15mutants. Among the plants witha reversion of the typical hst-15 phenotype weidentifieda new mutant allele of the F-box HAWAIIAN SKIRTencoding gene. HWS has been previously linked to miRNA biogenesis,but its role remains uncertain. Additionally, plants constitutively expressing full-length HWS—but not a truncated version lacking the F-box domain—showmorphological and molecular phenotypes resembling those of mutants defective in miRNA biogenesis and activity. Here, we explore the molecular crosstalk betweenHWS and HST to regulate the miRNA pathway. We found that HWSis capable of interacting with different components of mediator complex in vivopossibly promoting its degradation. Our data suggestthat HWS does not directly affect HST stability but rather the pathway downstream of this protein.