NAC1 Maintains Root Meristem Activity by Repressing the Transcription of E2Fa in Arabidopsis

Root meristem is a reserve of undifferentiated cells which guide root development. To maintain root meristem identity and therefore continuous root growth, the rate of cell differentiation must coordinate with the rate of generation of new cells. The E2 promoter-binding factor a (E2Fa) has been shown to regulate root growth through controlling G1/S cell cycle transitions in Arabidopsis thaliana. Here, we found that NAC1, a member of the NAM/ATAF/CUC family of transcription factors, regulated root growth by directly repressing the transcription of E2Fa. Loss of NAC1 triggers an up-regulation of the E2Fa expression and causes a reduced meristem size and short-root phenotype, which are largely rescued by mutation of E2Fa. Further analysis showed that NAC1 was shown to regulate root meristem by controlling endopolyploidy levels in an E2Fa-dependent manner. This study provides evidence to show that NAC1 maintains root meristem size and root growth by directly repressing the transcription of E2Fa in Arabidopsis.