Search for: All records

Ethyl methanesulfonate (EMS) mutagenesis offers important advantages for improving crops, such as cotton, with limited diversity in elite gene pools. EMS-induced point mutations are less frequently associated with deleterious traits than alleles from wild or exotic germplasm. From 157 mutant lines that have significantly improved fiber properties, we focused on nine mutant lines here. A total of eight populations were developed by crossing mutant lines in different combinations into GA230 (GA2004230) background. Multiple lines in each population were significantly improved for the fiber trait that distinguished the donor parent(s), demonstrating that an elite breeding line (GA230) could be improved for fiber qualities using the mutant lines. Genotypes improved for multiple fiber traits of interest suggesting that allele pyramiding is possible. Compared to midparent values, individual progeny in the population conferred fiber quality improvements of as much as 31.7% (in population O) for micronaire (MIC), 16.1% (in population P) for length, 22.4% (in population K) for strength, 4.1% (in population Q) for uniformity, 45.8% (in population N) for elongation, and 13.9% (in population O) for lint percentage (lint%). While further testing for stability of the phenotype and estimation of yield potential is necessary, mutation breeding shows promise as an approach to reduce the problem of the genetic bottleneck of upland cotton. The populations developed here may also contribute to identifying candidate genes and causal mutations for fiber quality improvement. 

Abstract Background Cotton fibers provide a powerful model for studying cell differentiation and elongation. Each cotton fiber is a singular and elongated cell derived from epidermal-layer cells of a cotton seed. Efforts to understand this dramatic developmental shift have been impeded by the difficulty of separation between fiber and epidermal cells. Results Here we employed laser-capture microdissection (LCM) to separate these cell types. RNA-seq analysis revealed transitional differences between fiber and epidermal-layer cells at 0 or 2 days post anthesis. Specifically, down-regulation of putative cell cycle genes was coupled with upregulation of ribosome biosynthesis and translation-related genes, which may suggest their respective roles in fiber cell initiation. Indeed, the amount of fibers in cultured ovules was increased by cell cycle progression inhibitor, Roscovitine, and decreased by ribosome biosynthesis inhibitor, Rbin-1. Moreover, subfunctionalization of homoeologs was pervasive in fiber and epidermal cells, with expression bias towards 10% more D than A homoeologs of cell cycle related genes and 40–50% more D than A homoeologs of ribosomal protein subunit genes. Key cell cycle regulators were predicted to be epialleles in allotetraploid cotton. MYB-transcription factor genes displayed expression divergence between fibers and ovules. Notably, many phytohormone-related genes were upregulated in ovules and down-regulated in fibers, suggesting spatial-temporal effects on fiber cell development. Conclusions Fiber cell initiation is accompanied by cell cycle arrest coupled with active ribosome biosynthesis, spatial-temporal regulation of phytohormones and MYB transcription factors, and homoeolog expression bias of cell cycle and ribosome biosynthesis genes. These valuable genomic resources and molecular insights will help develop breeding and biotechnological tools to improve cotton fiber production. 

Cotton bacterial blight (CBB), caused by the pathogenXanthomonas citrisubsp.malvacearum(Xcm), can inflict significant damage to cotton (Gossypium hirsutumL.) production. Previously, we identified and mapped the broad‐spectrum CBB‐resistant locusBB‐13on the long arm of chromosome D02 using array‐based single nucleotide polymorphisms (SNPs). In the current study, linked SNPs were converted into easily assayable Kompetitive Allele‐Specific PCR (KASP) markers to enable efficient detection and marker‐assisted selection of alleles at theBB‐13locus. The KASP marker's efficiency in detecting theBB‐13resistant gene was validated using an Upland cotton diversity panel of 72 accessions phenotyped withXcmrace 18. The KASP marker NCBB‐KASP4, derived from the CottonSNP63K array‐based marker i25755Gh that is closely associated withBB‐13, predicted the CBB response phenotypes with an error rate of 4.17% in the diversity panel. Additionally, two independent biparental recombinant inbred line populations segregating for resistance toXcmrace 18 were used for KASP marker validation and to test their utility in detecting the presence of theBB‐13locus in the resistant accession CABD3CABCH‐1‐89. NCBB‐KASP4, validated across breeding populations and broad germplasm, is a reliable KASP marker for detection and testing ofBB‐13locus in cotton. Further, diagnostic array‐based SNP marker i25755Gh's allele pattern and the potential CBB response is described for 875Gossypiumaccessions. These SNP‐based phenotypic predictions for 875 accessions along with disease response phenotypes toXcmrace 18 for 253 accessions provide a reference for CBB resistance in diverse cotton germplasm in the United States.

 

Polyploidy is an evolutionary innovation for many animals and all flowering plants, but its impact on selection and domestication remains elusive. Here we analyze genome evolution and diversification for all five allopolyploid cotton species, including economically important Upland and Pima cottons. Although these polyploid genomes are conserved in gene content and synteny, they have diversified by subgenomic transposon exchanges that equilibrate genome size, evolutionary rate heterogeneities and positive selection between homoeologs within and among lineages. These differential evolutionary trajectories are accompanied by gene-family diversification and homoeolog expression divergence among polyploid lineages. Selection and domestication drive parallel gene expression similarities in fibers of two cultivated cottons, involving coexpression networks andN⁶-methyladenosine RNA modifications. Furthermore, polyploidy induces recombination suppression, which correlates with altered epigenetic landscapes and can be overcome by wild introgression. These genomic insights will empower efforts to manipulate genetic recombination and modify epigenetic landscapes and target genes for crop improvement.