Fig. 8: Functional differentiation of GhCIPK6D1 and GhCIPK6D3 in regulating drought resistance of cotton.

After two WGDs, four CIPK6 genes remained in G. raimondii and G. arboretum, after quadrupling, eight CIPK6 genes were formed in upland cotton (G. hirsutum), and the expression of GhCIPK6D1 and GhCIPK6D3 and their biological functions in response to drought were sub-functionalized. Although the basal expression of GhCIPK6D1 was very low, it was greatly up-regulated by drought stress, and its interacting protein GhCBL1A1 was also up-regulated. In overexpression plants (GhCBL1A1-GhCIPK6D1), the downstream target protein in the cell membrane may be phosphorylated by GhCIPK6D1, which inhibits guard cell K⁺ efflux, increases the stomatal opening of leaves, accelerates the water loss, and plants exhibit drought sensitivity. However, the basal expression of GhCIPK6D3 was high, and also up-regulated by drought, and its interacting protein gene GhCBL2A1 was also up-regulated. In overexpression plants (GhCBL2A1-GhCIPK6D3), the downstream target protein in the vacuole membrane might was phosphorylated by GhCIPK6D3, which influences the K⁺ flux, resulting in closure of guard cells, and plants exhibit drought tolerance. GhCIPK6D1 is the likely progenitor of GhCIPK6D3 which evolved from GhCIPK6D1. These results show that different cotton family genes have evolved subfunctions to adapt to environmental changes. The figure Created with BioRender.com released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license.