Plant non-specific lipid transfer proteins (nsLTPs) are involved in many biological processes. In this study, 51, 47 and 91 nsLTPs were identified in Gossypium arboreum, G. raimondii and their descendant allotetraploid G. hirsutum, respectively. All the nsLTPs were phylogenetically divided into 8 distinct subfamilies. Besides, the recent duplication, which is considered cotton-specific whole genome duplication, may have led to nsLTP expansion in Gossypium. Both tandem and segmental duplication contributed to nsLTP expansion in G. arboreum and G. hirsutum, while tandem duplication was the dominant pattern in G. raimondii. Additionally, the interspecific orthologous gene pairs in Gossypium were identified. Some GaLTPs and GrLTPs lost their orthologs in the At and Dt subgenomes, respectively, of G. hirsutum. The distribution of these GrLTPs and GaLTPs within each subfamily was complementary, suggesting that the loss and retention of nsLTPs in G. hirsutum might not be random. Moreover, the nsLTPs in the At and Dt subgenomes might have evolved symmetrically. Furthermore, both intraspecific and interspecific orthologous genes showed considerable expression variation, suggesting that their functions were strongly differentiated. Our results lay an important foundation for expansion and evolutionary analysis of the nsLTP family in Gossypium, and advance nsLTP studies in other plants, especially polyploid plants.

Drought stress significantly limits cotton growth and production due to the necessity of water at every stage of crop growth. Hence, it is essential to identify tolerant genetic resources and understand the mechanisms of drought tolerance in economically and socially important plants such as cotton. In this study, molecular and physio-biochemical investigations were conducted by analyzing different parameters by following standard protocols in three different cotton species, namely TM-1 (Gossypium hirsutum), Zhongmian-16 (Gossypium arboreum), and Pima4-S (Gossypium barbadense). Drought stress significantly decreased plant growth, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), maximum photochemical efficiency of PSII (Fv/Fm), and relative water content. TM-1 resulted in more tolerance than the other two species. The accumulation of proline, soluble proteins, soluble sugars, hydrogen peroxide (H2O2), and superoxide radicals (O2•−) increased significantly in TM-1. In addition, TM-1 maintained the integrity of the chloroplast structure under drought conditions. The relative expression level of drought-responsive genes including coding for transcription factors and other regulatory proteins or enzymes controlling genes (ERF, ERFB, DREB, WRKY6, ZFP1, FeSOD, CuZnSOD, MAPKKK17, P5CR, and PRP5) were higher in TM-1 under drought, conferring a more tolerant status than in Zhongmian-16 and Pima4-S. The findings of this research could be utilized for predicting a tolerant cotton genotype as well as evaluating prospective cotton species in the variety development program.

Cotton is a premium source of natural fiber and is considered Bwhite gold^in the textile industry. Fiber length, strength and fineness are the key considerations for the industry. Longer fibers are machine friendly because they are easily spinnable. Recent advancements in genetic engineering, including the development of DNA markers and quantitative trait loci (QTLs), together with genome sequencing and gene expression profiling, have provided new avenues for improving fiber production and quality. In plants, sucrose synthase (SUS) is the key enzyme that catalyzes the reversible cleavage of sucrose and uridine diphosphate (UDP) into fructose and UDP-glucose. Sucrose is the main mobile sugar in plants moving from source to sink. It regulates resource partitioning between active sinks, especially in cotton embryos and fibers, and therefore is directly involved in determining fiber yield and seed quality. SUS actively takes part in regulating the competition for nutrients among sink tissues through balancing osmotic potentials by providing hexoses and an efficient supply of UDP-glucose the substrate for cellulose synthase. Cotton transformation has been used to improve fiber characteristics by altering cell wall properties through the manipulation of expression of fiber genes. Overexpression of the SUS gene from natural or synthetic origins in cotton can be an excellent way to solve potential problems associated with poor fiber length and other fiber quality traits. Increased SUS activity can result in more hexoses, increasing the osmotic potential and thereby driving the water influx that creates high turgor pressure in fiber cells resulting in enhanced fiber elongation. Moreover, increased SUS gene transcript levels in vegetative tissues of the plant will elevate seedling biomass and seed number. Fiber length and seed number both contribute towards final yield and the SUS genes as key regulators of sink strength in cotton perform this dual function that is directly related to cotton productivity. Hence manipulation of the SUS gene family is considered a promising approach to improve cotton fiber yield and quality. This review focuses on the biochemical and physiological roles of the SUS genes and there value for cotton fiber improvement.

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