GhIQD10 interacts with GhCaM7 to control cotton fiber elongation via calcium signaling

IQ67-domain (IQD) proteins function in plant defense and in organ development. The mechanisms by which they influence cotton fiber development are unknown. In the present study, GhIQD10 was expressed mainly in the transition period of cotton fiber development, and GhIQD10-overexpression lines showed shorter fibers. GhIQD10 interacted with GhCaM7 and the interaction was inhibited by Ca2+. In in vitro ovule culture, Ca2+ rescued the shorter-fiber phenotype of GhIQD10-overexpression lines, which were insensitive to the Ca2+ channel inhibitor verapamil and the Ca2+ pool release channel blocker 2-aminoethoxydiphenyl borate. We conclude that GhIQD10 affects cotton fiber elongation via Ca2+ signaling by interacting with GhCaM7. Brassinosteroid (BR) biosynthesis and signaling genes were up-regulated in GhIQD10-overexpression lines. Fiber development in these lines was not affected by epibrassinolide or the BR biosynthesis inhibitor brassinozole, indicating that the influence of GhIQD10 on fiber elongation was not associated with BR.