Abstract
In vascular plants, lateral roots (LRs) contribute to supporting aerial parts and absorbing water and nutrients in the soil. Previous studies have shown that the control of gene expression via auxin-responsive transcriptional factors ARF7, ARF19, and their repressor SOLITARY-ROOT(SLR)/IAA14 is important for LR initiation in Arabidopsis. However, it remains unknown how SLR/IAA14 represses the ARF7/19 activity. To identify the novel factors involved in this process, we screened for suppressor mutants of the lateral rootless mutant slr and isolated the suppressor of slr1 (ssl1) mutant that partially rescued the LR phenotype in slr. The ssl1 is a recessive mutation and the map-based cloning has shown that SSL1 encodes HASTY (HST), which is similar to the mammalian exportin-5 and is involved in miRNA processing and nuclear export in Arabidopsis.
We observed that ssl1 slr arf7 arf19 quadruple mutant formed no LRs, indicating that LR formation in ssl1 slr depends on ARF7/19 activity. In addition, the mutations in the miRNA biosynthesis partially rescued the LR phenotype in slr/+ heterozygous plants. These results indicate that miRNA regulation is involved in auxin-mediated LR formation.
