Sucrose synthase genes: a way forward for cotton fiber improvement

Cotton is a premium source of natural fiber and is considered "white 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.