Abstract
ABSTRACTHow plants determine the final size of growing cells is an important, yet unresolved, issue. Root hairs provide an excellent model system with which to study this as their final cell size is remarkably constant under constant environmental conditions. Previous studies have demonstrated that a basic helix-loop helix transcription factor ROOT HAIR DEFECTIVE 6-LIKE 4 (RSL4) promotes root hair growth, but how hair growth is terminated is not known. In this study, we demonstrate that a trihelix transcription factor GT-2-LIKE1 (GTL1) and its homolog DF1 repress root hair growth in Arabidopsis. Our transcriptional data, combined with genome-wide chromatin-binding data, show that GTL1 and DF1 directly bind the RSL4 promoter and regulate its expression to repress root hair growth. Our data further show that GTL1 and RSL4 regulate each other, as well as a set of common downstream genes, many of which have previously been implicated in root hair growth. This study therefore uncovers a core regulatory module that fine-tunes the extent of root hair growth by the orchestrated actions of opposing transcription factors.
Highlights
Plant cells often undergo extensive post-mitotic cell expansion and can reach up to several hundred-fold their original size (SugimotoShirasu and Roberts, 2003)
GTL1 and DF1 repress root hair growth through a ploidyindependent mechanism To explore the functional redundancy between GTL1 and DF1, we isolated an Arabidopsis T-DNA insertion mutant for DF1 that resulted in a null allele (Fig. S1A)
Our time-lapse analysis showed that the rate of root hair growth is comparable between wild type and gtl1-1 df1-1 but gtl1-1 df1-1 root hairs continue to grow after wildtype root hairs halt their growth (Fig. 1C)
Summary
Plant cells often undergo extensive post-mitotic cell expansion and can reach up to several hundred-fold their original size (SugimotoShirasu and Roberts, 2003). As for many other cell types in plants, root hair growth is often accompanied by an increase in nuclear DNA content, or ploidy, through successive rounds of endoreduplication (Breuer et al, 2007; Sugimoto-Shirasu et al, 2005, 2002). It is known, that root hair growth is ploidy independent to some degree as root hairs can elongate without changing their ploidy levels (Yi et al, 2010)
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