ROP-GEF signal transduction is involved in AtCAP1-regulated root hair growth

CAP1 ([Ca2+] cyt-associated protein kinase) is a member of the Arabidopsis CrRLK1L receptor-like kinase family, which has been characterized as functioning in regulating root hair polar growth. A deficiency of CAP1 results in short root hairs. In order to understand the regulation mechanism of CAP1 in root hair growth, Y2H and BiFC assays were used, and guanine nucleotide exchange factor1 (GEF1) was identified as the interacting factor of CAP1. Overexpression of GEF1 can rescue cap1-1 short root hair to some extent. GEF can activate Rho-related GTPase of plants (ROPs), and ROPs play important roles in plant signal transduction and developmental regulation. The total ROP protein content of cap1-1 roots was less than that of the wild type. Overexpression of ROP2 or 6 can partially restore cap1-1 root hair growth. Our results thus suggest that the ROP-GEF signalling pathway is involved in CAP1-regulated root hair tip growth and development.