Salinity is a major abiotic stress that restricts cotton growth and affects fiber yield and quality. Although studies on salt tolerance have achieved great progress in cotton since the completion of cotton genome sequencing, knowledge about how cotton copes with salt stress is still scant. S-adenosylmethionine (SAM) plays important roles in many organelles with the help of the SAM transporter, and it is also a synthetic precursor for substances such as ethylene (ET), polyamines (PAs), betaine, and lignin, which often accumulate in plants in response to stresses. This review focused on the biosynthesis and signal transduction pathways of ET and PAs. The current progress of ET and PAs in regulating plant growth and development under salt stress has been summarized. Moreover, we verified the function of a cotton SAM transporter and suggested that it can regulate salt stress response in cotton. At last, an improved regulatory pathway of ET and PAs under salt stress in cotton is proposed for the breeding of salt-tolerant varieties.

Introduction: Cotton is an important economic crop to provide natural fibers as raw materials to textile industry, and is significantly affected by biotic and abiotic stress during the whole growth stage, in which Verticillium wilt (VW) caused by Verticillium dahliae is one of the most destructive disease to lead to a significant yield reduction. Heat shock proteins (Hsps) are important molecular chaperones, and play crucial roles in plant growth, development, resistance to biotic and abiotic stress. Hsp40 and Hsp70 are two key Hsps in cell chaperone network, however, the function and regulatory mechanism of Hsp40 and Hsp70 members in VW resistance and abiotic stress in cotton are largely unknown.Methods and Results: Herein, a systematic and comprehensive analysis of Hsp40s and Hsp70s in four cotton species of Gossypium arboretum, G. raimondii, G. hirsutum, and G. barbadense were performed. A total of 291 Hsp40s and 171 Hsp70s identified in four Gossypium species. Sequence analysis revealed that all Hsp40 proteins contained J domain that provides the binding sites to Hsp70. Protein-protein interaction prediction analysis displayed that GhHsp40-55 might interact with GhHsp70-2 and GhHsp70-13, suggesting their potential function as protein complex. Promoter cis-acting element analysis demonstrated that multiple cis-elements related to disease and stress response consists in GhHsp40 and GhHsp70 promoters. Further expression analysis showed that eight GhHsp40s (Hsp40-2,4,8,11,20,23,53,55) and seven GhHsp70s (Hsp70-2,3,6,8,13,19,22) were up-regulated after V. dahliae infection. In addition, five GhHsp40s (Hsp40-2,8,11,53,55) and four GhHsp70s (Hsp70-3,6,8,13) were up-regulated after salt treatment, six GhHsp40s (Hsp40-4,11,20,23) and three GhHsp70s (Hsp70-2,8,19) were up-regulated after drought treatment, four GhHsp40s (Hsp40-2,11,20,23) and four GhHsp70s (Hsp70-3,6,19,22) were up-regulated after temperature treatment, suggesting these Hsps have possible important function in the process of abiotic stress response.Discussion: Our results lay a foundation for understanding the function of Hsp40 and Hsp70 in the resistance against V. dahliae and abiotic stress, and elucidating the regulatory mechanism of the protein complex, evolution and molecular mechanism under stress.

Annexins (ANNs) are a structurally conserved protein family present in almost all plants. In the present study, 27 GhANNs were identified in cotton and were unevenly distributed across 14 chromosomes. Transcriptome data and RT-qPCR results revealed that multiple GhANNs respond to at least two abiotic stresses. Similarly, the expression levels of GhANN4 and GhANN11 were significantly upregulated under heat, cold, and drought stress. Using virus-induced gene silencing (VIGS), functional characterization of GhANN4 and GhANN11 revealed that, compared with those of the controls, the leaf wilting of GhANN4-silenced plants was more obvious, and the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were lower under NaCl and PEG stress. Moreover, the expression of stress marker genes (GhCBL3, GhDREB2A, GhDREB2C, GhPP2C, GhRD20-2, GhCIPK6, GhNHX1, GhRD20-1, GhSOS1, GhSOS2 and GhSnRK2.6) was significantly downregulated in GhANN4-silenced plants after stress. Under cold stress, the growth of the GHANN11-silenced plants was significantly weaker than that of the control plants, and the activities of POD, SOD, and CAT were also lower. However, compared with those of the control, the elasticity and orthostatic activity of the GhANN11-silenced plants were greater; the POD, SOD, and CAT activities were higher; and the GhDREB2C, GhHSP, and GhSOS2 expression levels were greater under heat stress. These results suggest that different GhANN family members respond differently to different types of abiotic stress.

This study identified 13 GhTIR1/AFB members in G. hirsutum through bioinformatics methods and divided them into three subgroups by phylogenetic tree analysis. Motif and gene structure analysis showed that the genes in this family were highly conserved. Promoter cis-acting element analysis found that the promoters of GhTIR1/AFBs contained a large number of cis-acting elements in response to growth and development and abiotic stress. Further RT-qPCR results showed that GhTIR1/AFB genes responded to various abiotic stresses such as IAA, ABA, cold, and heat, and the expression levels of each gene changed obviously, especially Gh_D08G0763 (GhTIR1), which responded significantly to cold injury. Using VIGS (virus-induced gene silencing) technology to silence Gh_D08G0763 in the cold-tolerant cotton variety ZM36, it was found that the resistance of ZM36 to cold damage was significantly reduced. The physiological response mechanism of the Gh_D08G0763 in resisting cold damage was further analyzed through trypan blue staining of leaves and determination of enzyme activity levels. This study provided effective genetic resources for cotton cold-tolerance breeding.

Cotton is one of the most important fiber and oil crops in the world. Chloroplast genomes harbor their own genetic materials and are considered to be highly conserved. Transfer RNAs (tRNAs) act as “bridges” in protein synthesis by carrying amino acids. Currently, the variation and evolutionary characteristics of tRNAs in the cotton chloroplast genome are poorly understood. Here, we analyzed the structural variation and evolution of chloroplast tRNA (cp tRNA) based on eight diploid and two allotetraploid cotton species. We also investigated the nucleotide evolution of chloroplast genomes in cotton species. We found that cp tRNAs in cotton encoded 36 or 37 tRNAs, and 28 or 29 anti-codon types with lengths ranging from 60 to 93 nucleotides. Cotton chloroplast tRNA sequences possessed specific conservation and, in particular, the Ψ-loop contained the conserved U-U-C-X3-U. The cp tRNAs of Gossypium L. contained introns, and cp tRNA^Ile contained the anti-codon (C-A-U), which was generally the anti-codon of tRNA^Met. The transition and transversion analyses showed that cp tRNAs in cotton species were iso-acceptor specific and had undergone unequal rates of evolution. The intergenic region was more variable than coding regions, and non-synonymous mutations have been fixed in cotton cp genomes. On the other hand, phylogeny analyses indicated that cp tRNAs of cotton were derived from several inferred ancestors with greater gene duplications. This study provides new insights into the structural variation and evolution of chloroplast tRNAs in cotton plants. Our findings could contribute to understanding the detailed characteristics and evolutionary variation of the tRNA family.

Phosphatidylinositol 4-phosphate 5-kinases (PIP5Ks), essential enzymes in the phosphatidylinositol signaling pathway, are crucial for the abiotic stress responses and the overall growth and development of plants. However, the GhPIP5Ks had not been systematically studied, and their function in upland cotton was unknown. This study identified a total of 28 GhPIP5Ks, and determined their chromosomal locations, gene structures, protein motifs and cis-acting elements via bioinformatics analysis. A quantitative real-time PCR (qRT‒PCR) analysis showed that most GhPIP5Ks were upregulated under different stresses. A virus-induced gene silencing (VIGS) assay indicated that the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were significantly decreased, while malondialdehyde (MDA) content were significantly increased in GhPIP5K2- and GhPIP5K22-silenced upland cotton plants under abiotic stress. Furthermore, the expression of the stress marker genes GhHSFB2A, GhHSFB2B, GhDREB2A, GhDREB2C, GhRD20-1, GhRD29A, GhBIN2, GhCBL3, GhNHX1, GhPP2C, GhCBF1, GhSnRK2.6 and GhCIPK6 was significantly decreased in the silenced plants after exposure to stress. These results revealed that the silencing of GhPIP5K2 and GhPIP5K22 weakened the tolerance to abiotic stresses. These discoveries provide a foundation for further inquiry into the actions of the GhPIP5K gene family in regulating the response and resistance mechanisms of cotton to abiotic stresses.