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Background: Cotton (Gossypium sp.) has been cultivated for centuries for its spinnable fibers, but its seed oil also possesses untapped economic potential if, improvements could be made to its oleic acid content., Results: Previous studies, including those from our laboratory, identified pima accessions containing approximately doubled levels of seed oil oleic acid, compared to standard upland cottonseed oil. Here, the molecular properties of a fatty acid desaturase encoded by a mutant allele identified by genome sequencing in an earlier analysis were analyzed. The mutant sequence is predicted to encode a C-terminally truncated protein lacking nine residues, including a predicted endoplasmic reticulum membrane retrieval motif. We determined that the mutation was caused by a relatively recent movement of a Ty1/copia type retrotransposon that is not found associated with this desaturase gene in other sequenced cotton genomes. The mutant desaturase, along with its repaired isozyme and the wild-type A-subgenome homoeologous protein were expressed in transgenic yeast and stably transformed Arabidopsis plants. All full-length enzymes efficiently converted oleic acid to linoleic acid. The mutant desaturase protein produced only trace amounts of linoleic acid, and only when strongly overexpressed in yeast cells, indicating that the missing C-terminal amino acid residues are not strictly required for enzyme activity, yet are necessary for proper subcellular targeting to the endoplasmic reticulum membrane., Conclusion: These results provide the biochemical underpinning that links a genetic lesion present in a limited group of South American pima cotton accessions and their rare seed oil oleic acid traits. Markers developed to the mutant desaturase allele are currently being used in breeding programs designed to introduce this trait into agronomic upland cotton varieties., (© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Background: Weed management is critical to global crop production and is complicated by rapidly evolving herbicide resistance in weeds. New sources of herbicide resistance are needed for crop plants so that applied herbicides can be rotated or combined to thwart the evolution of resistant weeds. The diverse family of cytochrome P450 proteins has been suggested to be a source of detoxifying herbicide metabolism in both weed and crop plants, and greater understanding of these genes will offer avenues for crop improvement and novel weed management practices., Results: Here, we report the identification of CYP749A16 (Gh_D10G1401) which is responsible for the natural tolerance exhibited by most cotton, Gossypium hirsutum L., cultivars to the herbicide trifloxysulfuron sodium (TFS, CGA 362622, commercial formulation Envoke). A 1-bp frameshift insertion in the third exon of CYP749A16 results in the loss of tolerance to TFS. The DNA marker designed from this insertion perfectly co-segregated with the phenotype in 2145 F 2 progeny of a cross between the sensitive cultivar Paymaster HS26 and tolerant cultivar Stoneville 474, and in 550 recombinant inbred lines of a multi-parent advanced generation inter-cross population. Marker analysis of 382 additional cotton cultivars identified twelve cultivars containing the 1-bp frameshift insertion. The marker genotypes matched perfectly with phenotypes in 188 plants from the selected twelve cultivars. Virus-induced gene silencing of CYP749A16 generated sensitivity in the tolerant cotton cultivar Stoneville 474., Conclusions: CYP749A16 located on chromosome D10 is required for TFS herbicide tolerance in cotton. This finding should add to the repertoire of tools available to farmers and breeders for the advancement of agricultural productivity.

Background: Individual fiber strength is an important quality attribute that greatly influences the strength of the yarn spun from cotton fibers. Fiber strength is usually measured from bundles of fibers due to the difficulty of reliably measuring strength from individual cotton fibers. However, bundle fiber strength (BFS) is not always correlated with yarn strength since it is affected by multiple fiber properties involved in fiber-to-fiber interactions within a bundle in addition to the individual fiber strength. Molecular mechanisms responsible for regulating individual fiber strength remain unknown. Gossypium hirsutum near isogenic lines (NILs), MD52ne and MD90ne showing variations in BFS provide an opportunity for dissecting the regulatory mechanisms involved in individual fiber strength., Results: Comprehensive fiber property analyses of the NILs revealed that the superior bundle strength of MD52ne fibers resulted from high individual fiber strength with minor contributions from greater fiber length. Comparative transcriptome analyses of the NILs showed that the superior bundle strength of MD52ne fibers was potentially related to two signaling pathways: one is ethylene and the interconnected phytohormonal pathways that are involved in cotton fiber elongation, and the other is receptor-like kinases (RLKs) signaling pathways that are involved in maintaining cell wall integrity. Multiple RLKs were differentially expressed in MD52ne fibers and localized in genomic regions encompassing the strength quantitative trait loci (QTLs). Several candidate genes involved in crystalline cellulose assembly were also up-regulated in MD52ne fibers while the secondary cell wall was produced., Conclusion: Comparative phenotypic and transcriptomic analyses revealed differential expressions of the genes involved in crystalline cellulose assembly, ethylene and RLK signaling pathways between the MD52ne and MD90ne developing fibers. Ethylene and its phytohormonal network might promote the elongation of MD52ne fibers and indirectly contribute to the bundle strength by potentially improving fiber-to-fiber interactions. RLKs that were suggested to mediate a coordination of cell elongation and SCW biosynthesis in other plants might be candidate genes for regulating cotton fiber cell wall assembly and strength.

Background: Cotton fiber length is a key determinant of fiber quality for the textile industry. Understanding the molecular basis of fiber elongation would provide a means for improvement of fiber length. Ligon lintless-1 (Li 1 ) and Ligon lintless-2 (Li 2 ) are monogenic and dominant mutations, that result in an extreme reduction in the length of lint fiber to approximately 6 mm on mature seeds. In a near-isogenic state with wild type (WT) cotton these two short fiber mutants provide an excellent model system to study mechanisms of fiber elongation., Results: We used next generation sequencing (RNA-seq) to identify common fiber elongation related genes in developing fibers of Li 1 and Li 2 mutants growing in the field and a greenhouse. We found a large number of differentially expressed genes common to both mutants, including 531 up-regulated genes and 652 down-regulated genes. Major intrinsic proteins or aquaporins were one of the most significantly over-represented gene families among common down-regulated genes in Li 1 and Li 2 fibers. The members of three subfamilies of aquaporins, including plasma membrane intrinsic proteins, tonoplast intrinsic proteins and NOD26-like intrinsic proteins were down-regulated in short fiber mutants. The osmotic concentration and the concentrations of soluble sugars were lower in fiber cells of both short fiber mutants than in WT, whereas the concentrations of K+ and malic acid were significantly higher in mutants during rapid cell elongation., Conclusions: We found that the aquaporins were the most down-regulated gene family in both short fiber mutants. The osmolality and concentrations of soluble sugars were less in saps of Li 1 - Li 2 , whereas the concentrations of malic acid, K+ and other detected ions were significantly higher in saps of mutants than in WT. These results suggest that higher accumulation of ions in fiber cells, reduced osmotic pressure and low expression of aquaporins, may contribute to the cessation of fiber elongation in Li 1 and Li 2 short-fiber mutants. The research presented here provides new insights into osmoregulation of short fiber mutants and the role of aquaporins in cotton fiber elongation.