A Novel Calmodulin-Interacting Domain of Unknown Function 506 Protein Represses Root Hair Elongation in Arabidopsis

The study explored the role of the novel calmodulin-interacting protein AtRXR3 in repressing root hair elongation in Arabidopsis under phosphorus deficiency. AtRXR3, part of the DUF506 gene family, inhibited root hair growth by interacting with RSL4 and cytosolic calmodulins, differing from AtRXR1's mechanism involving a small GTPase. RXR3 expression was upregulated in response to phosphorus deprivation and auxin, independent of PHR1 and PHL1 transcription factors. Overexpression of RXR3 resulted in shorter root hairs, while mutants had longer root hairs and increased phosphorus content, indicating RXR3's role as a growth repressor affecting phosphorus uptake. The study involved measurements from 10 seedlings per genotype and confirmed RXR3's interaction with calmodulins, suggesting its involvement in CaM-mediated pathways and highlighting its distinct function from RXR1 in the phosphorus limitation-induced root hair growth regulatory network.