AT-hook motif nuclear localized transcription factors function redundantly in promoting root growth through modulation of redox homeostasis

AT-hook motif nuclear localized (AHL) proteins are evolutionarily conserved transcription factors in plants. Much of our understanding about this family has come from studies on clade A genes. To elucidate the functions of clade B genes, we first analyzed their spatial expression patterns using transgenic plants expressing a nuclear localized GFP under the control of their own promoters. AHL1, 2, 6, 7 and 10 were further functionally characterized due to their high expression in the root apical meristem. Through mutant analysis and transgenic studies, we showed that these genes have the ability to promote root growth. Using yeast one-hybrid and dual luciferase assays, we demonstrated that AHL1, 2, 6, 7 and 10 are transcription activators and this activity is required for their roles in promoting root growth. Through transcriptome analysis, histochemical staining and molecular genetics experiments we found that AHL10 regulates redox homeostasis via direct regulation of glutathione transferase (GST) genes. Strikingly, when GSTF2 expression was reduced by RNAi, the short-root phenotype in AHL10-SRDX expressing plants was largely rescued. Based on these results, we conclude that AHL genes function redundantly in promoting root growth through direct regulation of redox homeostasis.