A novel Calmodulin-interacting Domain of Unknown Function 506 protein
represses root hair elongation in Arabidopsis
DUF506 proteins are omnipresent in higher plants. Phosphorus (P)
stress-inducible AtRXR1/REPRESSOR OF EXCESSIVE ROOT HAIR ELONGATION 1
gene, as the first functionally characterized DUF506 gene, is proved to
inhibit root hair elongation through interaction of RXR2/RabD2c GTPase.
However, the knowledge of other P-responsive DUF506 genes is still
limited. Here, we identify four additional P-inducible DUF506 genes and
select two of candidates for functional investigation. Expression
analysis results reveal that both of candidates are induced by auxin.
At3g07350, the duplicated pair of RXR1, expresses ubiquitously in
seedlings under P-stress, whereas At1g62420 is mainly induced in roots.
Overexpression and knockout mutants of At1g62420, which is called RXR3,
exhibit shorter or longer root hair length, respectively. Cellular
imaging results demonstrate RXR3 localizes in root epidermal cells.
ChIP, synthetic peptide treatment and qRT-PCR assay results indicate
RXR3 is transcriptionally activated by RSL4 or RALF1. BiFC and
CaM-binding assay suggest that RXR3 interacts with various CaMs in
presence of Ca2+. Moreover, the frequencies of [Ca2+]cyt in rxr3
mutants are approximately 20% higher compared to that of wild type.
Taken together, our results illustrate a divergent mechanism by which
RSL4-directed RXR3 interacts with calmodulin and functions in parallel
of RXR1, to prevent root hair excessive growth.