Fiber-specific overexpression of GhACO1 driven by E6 promoter improves cotton fiber quality and yield

Abstract

Cotton (Gossypium hirsutum) is the most important fiber crop globally and there is an incentive to improve cotton fiber yield and quality to meet the growing market demand. 1-Aminocyclopropane-1-Carboxylic Acid Oxidase (ACO) has been identified as a rate-limiting enzyme in the biosynthesis of ethylene that is known to play a pivotal regulatory role in fiber development. According to transcriptomic data analysis, GhACO1 is preferentially expressed at fiber elongation stage in a number of G. hirsutum varieties, suggestive of its involvement in regulating fiber development. Ethylene is known to cause premature senescence, and to abrogate its potential negative effects on plant growth by constitutive overexpression of GhACO1, a fiber-specific promoter E6 that imparts strong transcriptional activity in fiber elongation stage was employed to drive GhACO1 expression to improve fiber quality. The E6::GhACO1 cotton transgenic lines showed substantial improvements in fiber length, fiber strength and fiber yield relative to wild type. Exogenous application of pyrazinecarboxylic acid that is an effective inhibitor of ACO enzyme inhibited fiber elongation in ovule culture, validating that GhACOs may improve fiber quality by increasing ethylene levels. Furthermore, RNA-Seq analysis showed that upregulation of GhACO1 can activate the transcription of genes that are involved in hydrogen peroxide metabolism, cell wall loosening and cytoskeleton arrangement, thereby promoting fiber elongation. These findings suggest that GhACO1 is a key regulator of fiber development, and the application of “E6::GhACO1” strategy breaks the negative correlation between fiber quality and fiber yield, providing a novel route in formulating fiber improvement strategies in cotton.