Brassinosteroid signaling regulates phosphate starvation-induced malate secretion in plants

The cotton protein GhIQD21 interacts with GhCaM7 and modulates organ morphogenesis in Arabidopsis by influencing microtubule stability

KEY MESSAGE

GhIQD21, a cotton IQ67-domain protein, interacts with GhCaM7 and alters organ shape in Arabidopsis by modulating microtubule stability. Calcium ion (Ca²⁺) and the calcium sensor calmodulin play crucial roles in the growth and development of plants. GhCaM7, a calmodulin in upland cotton (Gossypium hirsutum L.), is highly expressed in cotton fiber cells during the rapid elongation period and plays an important role in fiber cell development. In this study, we screened for GhCaM7-interacting proteins and identified GhIQD21, which contains a typical IQ67-domain. GhIQD21 was preferentially expressed at the fiber rapid elongation stage, and the protein localized to microtubules (MTs). Ectopic expression of GhIQD21 in Arabidopsis resulted in shorter leaves, petals, siliques, and plant height, thicker inflorescences, and more trichomes when compared with wild type (WT). Further investigation indicated that the morphogenesis of leaf epidermal cells and silique cells was altered. There was less consistency in the orientation of cortical microtubules in cotyledon and hypocotyl epidermal cells. Furthermore, compared with WT, transgenic seedling hypocotyls were more sensitive to oryzalin, a MT depolymerization drug. These results indicated that GhIQD21 is a GhCaM7-interacting protein located in MTs and that it plays a role in plant growth and potentially cotton fiber development. This study provides a foundation for further studies of the function and regulatory mechanism of GhIQD21 in fiber cell development.

Overexpression of cotton Trihelix transcription factor GhGT-3b_A04 enhances resistance to Verticillium dahliae and affects plant growth in Arabidopsis thaliana

Verticillium wilt is a soil-borne fungal disease that severely affects cotton fiber yield and quality. Herein, a cotton Trihelix family gene, GhGT-3b_A04, was strongly induced by the fungal pathogen Verticillium dahliae. Overexpression of the gene in Arabidopsis thaliana enhanced the plant's resistance to Verticillium wilt but inhibited the growth of rosette leaves. In addition, the primary root length, root hair number, and root hair length increased in GhGT-3b_A04-overexpressing plants. The density and length of trichomes on the rosette leaves also increased. GhGT-3b_A04 localized to the nucleus, and transcriptome analysis revealed that it induced gene expression for salicylic acid synthesis and signal transduction and activated gene expression for disease resistance. The gene expression for auxin signal transduction and trichome development was reduced in GhGT-3b_A04-overexpressing plants. Our results highlight important regulatory genes for Verticillium wilt resistance and cotton fiber quality improvement. The identification of GhGT-3b_A04 and other important regulatory genes can provide crucial reference information for future research on transgenic cotton breeding.

Loss of function of VdDrs2, a P4-ATPase, impairs the toxin secretion and microsclerotia formation, and decreases the pathogenicity of Verticillium dahliae

Four P4-ATPase flippase genes, VdDrs2, VdNeo1, VdP4-4, and VdDnf1 were identified in Verticillium dahliae, one of the most devastating phytopathogenic fungi in the world. Knock out of VdDrs2, VdNeo1, and VdP4-4, or knock down of VdDnf1 significantly decreased the pathogenicity of the mutants in cotton. Among the mutants, the greatest decrease in pathogenicity was observed in ΔVdDrs2. VdDrs2 was localized to plasma membrane, vacuoles, and trans-Golgi network (TGN). In vivo observation showed that the infection of the cotton by ΔVdDrs2 was significantly delayed. The amount of two known Verticillium toxins, sulfacetamide, and fumonisin B1 in the fermentation broth produced by the ΔVdDrs2 strain was significantly reduced, and the toxicity of the crude Verticillium wilt toxins to cotton cells was attenuated. In addition, the defect of VdDrs2 impaired the synthesis of melanin and the formation of microsclerotia, and decreased the sporulation of V. dahliae. Our data indicate a key role of P4 ATPases-associated vesicle transport in toxin secretion of disease fungi and support the importance of mycotoxins in the pathogenicity of V. dahliae.

GhCYP710A1 Participates in Cotton Resistance to Verticillium Wilt by Regulating Stigmasterol Synthesis and Plasma Membrane Stability

Cotton is an important economic crop. Cotton Verticillium wilt caused by Verticillium dahliae seriously damages production. Phytosterols play roles in plant-pathogen interaction. To explore the function and related mechanism of phytosterols in the interaction between Verticillium dahliae and cotton plants, and the resistance to Verticillium wilt, in this study, we analyzed the changes of sterol composition and content in cotton roots infected by Verticillium dahliae, and identified the sterol C22-desaturase gene GhCYP710A1 from upland cotton. Through overexpressing and silencing the gene in cotton plant, and ectopically expressing the gene in Arabidopsis, we characterized the changes of sterol composition and the resistance to Verticillium wilt in transgenic plants. The infection of Verticillium dahliae resulted in the content of total sterol and each sterol category decreasing in cotton root. The ratio of stigmasterol to sitosterol (St/Si) increased, indicating that the conversion of sitosterol to stigmasterol was activated. Consistently, the expression level of GhCYP710A1 was upregulated after infection. The GhCYP710A1 has the conservative domain that is essential for sterol C22-desaturase in plant and is highly expressed in root and stem, and its subcellular location is in the endoplasmic reticulum. The ectopic expression of GhCYP710A1 gene promoted the synthesis of stigmasterol in Arabidopsis. The St/Si value is dose-dependent with the expression level of GhCYP710A1 gene. Meanwhile, the resistance to Verticillium wilt of transgenic Arabidopsis increased and the permeability of cell membrane decreased, and the content of ROS decreased after V991 (a strain of Verticillium dahliae) infection. Consistently, the resistance to Verticillium wilt significantly increased in the transgenic cotton plants overexpressing GhCYP710A1. The membrane permeability and the colonization of V991 strain in transgenic roots were decreased. On the contrary, silencing GhCYP710A1 resulted in the resistance to Verticillium wilt being decreased. The membrane permeability and the colonization of V991 were increased in cotton roots. The expression change of GhCYP710A1 and the content alteration of stigmasterol lead to changes in JA signal transduction, hypersensitivity and ROS metabolism in cotton, which might be a cause for regulating the Verticillium wilt resistance of cotton plant. These results indicated that GhCYP710A1 might be a target gene in cotton resistance breeding.