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Cotton is one of the most important economic and fiber crops in the world. KNOX is one class of universal transcription factors, which plays important roles in plant growth and development as well as response to different stresses. Although there are many researches on KNOXs in other plant species, there are few reports on cotton. In this study, we systematically and comprehensively identified all KNOX genes in upland cotton and its two ancestral species; we also studied their functions by employing RNA-seq analysis and virus-induced gene silence (VIGS). A total of 89 KNOX genes were identified from three cotton species. Among them, 44 were from upland cotton, 22 and 23 were found in its ancestral species G. raimondii and G. arboreum , respectively. Plant polyploidization and domestication play a selective force driving KNOX gene evolution. Phylogenetic analysis displayed that KNOX genes were evolved into three Classes. The intron length and exon number differed in each Class. Transcriptome data showed that KNOX genes of Class II were widely expressed in multiple tissues, including fiber. The majority of KNOX genes were induced by different abiotic stresses. Additionally, we found multiple cis -elements related to stress in the promoter region of KNOX genes. VIGS silence of GhKNOX4-A and GhKNOX22-D genes showed significant growth and development effect in cotton seedlings under salt and drought treatments. Both GhKNOX4-A and GhKNOX22-D regulated plant tolerance; silencing both genes induced oxidative stresses, evidenced by reduced SOD activity and induced leave cell death, and also enhanced stomatal open and water loss. Thus, GhKNOX4-A and GhKNOX22-D may contribute to drought response by regulating stomata opening and oxidative stresses. • A total of 89 KNOX genes were identified from upland cotton and its two ancestral species • Plant polyploidization and domestication play a selective force driving KNOX gene evolution • VIGS silence of GhKNOX4-A Gh and GhKNOX22-D genes showed significant growth and development effect in cotton seedlings under salt and drought treatment • Silencing GhKNOX4-A and GhKNOX22-D induced oxidative and abiotic stresses • GhKNOX4-A and GhKNOX22-D may contribute to drought response by regulating stomata opening and oxidative stresses [ABSTRACT FROM AUTHOR]

Cotton Verticillium wilt caused by Verticillium dahliae (V. dahliae) is one of the most destructive fungal diseases and is difficult to control. However, resistant germplasm resources are scarce in cotton. Many studies have shown that host-induced gene silencing (HIGS) is a practical and effective technology in crop disease prevention by silencing virulence genes of pathogens. Acetolactate synthase (ALS) contains a catalytic subunit ILV2 and a regulatory subunit ILV6, which catalyzes the first common step reaction in branched-chain amino acid (BCAA) biosynthesis. We identified two acetolactate synthases, VdILV2 and VdILV6, which are homologs of ILV2 and ILV6, respectively, in Magnaporthe oryzae. To characterize the function of VdILV2 and VdILV6 in V. dahliae , we suppressed their expression in the strong pathogenic isolate Vd991 by using HIGS technology. VdILV2- or VdILV6- silenced V. dahliae had a dramatic reduction in pathogenicity. The results indicated that VdILV2 and VdILV6 are involved in the pathogenicity of V. dahliae. HIGS of VdILV2 or VdILV6 provides a novel fungicide target and an effective control to resist Verticillium wilt caused by V. dahliae. • Cotton Verticillium wilt caused by Verticillium dahliae (V. dahliae) is one of the most destructive fungi diseases. • HIGS of VdILV2 and VdILV6 enhanced cotton resistance to Verticillium wilt. • VdILV2 and VdILV6 are involved in pathogenicity in V. dahliae. • HIGS of VdILV2 or VdILV6 provides an effective control to resist Verticillium Wilt caused by V. dahliae. [ABSTRACT FROM AUTHOR]

Grafting is a classical technique to increase plant stress resistance and yield in horticultural crops. This review takes cotton (Gossypium spp.) as an example to summarize the application of grafting in sustainable development for the following subjects: (1) cotton production, such as improving stress tolerance, increasing nutrient and water use efficiency, and cultivating cotton perennially for high yield; (2) cotton breeding, such as conserving and propagating special germplasms, utilizing heterosis, breeding new varieties, improving the survival rate of transplanted plantlets, and accelerating virus-induced gene silencing (VIGS); and (3) cotton physiology and molecular biology research, such as the mechanism underlying root-shoot communication. In particular, cotton is a unique non-horticultural field crop, which can grow annually or perennially, depending on winter temperature. Therefore, cotton grafting has some unique aspects, e.g., annual cotton cultivars can be used in perennial cultivation when grafted on cold-resistant rootstocks to improve the over-winter survival abilities, and graft-propagated male sterile plants can be used for multi-year heterosis utilization in near tropics, which could be used to build a sustainable agricultural system. Moreover, future promises associated with grafting have been presented and discussed, such as whether cotton grafting could promote the exchange of genetic material (especially DNA) between rootstock and scion, resulting in stable inheritable variations that remains to be verified by molecular genetics. • Cotton grafting has been widely used to study root-shoot communication mechanism. • Grafting may become a new technology for cotton germplasm innovation. • Grafting can be applied to sustainable production and perennial cultivation. • Grafting is important for reproduction of sterile cotton. [ABSTRACT FROM AUTHOR]