Project description:Purpose: The goal of this experiment was to use RNA-seq to compare the two commercial cotton species Gossypium hirsutum and Gossypium barbadense and determine what transcripts may account for the better fiber quality in the latter. Methods: RNA was extracted from Gossypium barbadense or Gossypium hirsutum fibers at 10, 15, 18, 21, and 28 days post anthesis. Paired-end, 100-bp RNA-seq was performed on an Illumina HiSeq2000 and the reads were mapped to the Gossypium raimondii genome at www.phytozome.net and non-homologous contig assemblies from Gossypium arboreum. Results from RNA-seq were combined with non-targeted metabolomics. Results: Approximately 38,000 transcripts were expressed (RPKM>2) in each fiber type and approximately 2,000 of these transcripts were differentially expressed in a cross-species comparison at each timepoint. Enriched Gene Ontology biological processes in differentially expressed transcripts suggested that Gh fibers were more stressed. Conclusions: Both metabolomic and transcriptomic data suggest that better mechanisms for managing reactive oxygen species contribute to the increased fiber length in Gossypium barbadense. This appears to result from enhanced ascorbate biosynthesis via gulono-1,4-lactone oxidase and ascorbate recycling via dehydroascorbate reductase.
Project description:Crop wild relatives are an important reservoir of natural biodiversity. However, incorporating wild genetic diversity into breeding programs is often hampered by reproductive barriers and a lack of accurate genomic information. We assembled a high-quality, accurately centromere-anchored genome of Gossypium anomalum, a stress-tolerant wild cotton species. We provided a strategy to discover and transfer agronomically valuable genes from wild diploid species to tetraploid cotton cultivars. With a (Gossypium hirsutum × G. anomalum)2 hexaploid as a bridge parent, we developed a set of 74 diploid chromosome segment substitution lines (CSSLs) of the wild cotton species G. anomalum in the G. hirsutum background. This set of CSSLs included 70 homozygous substitutions and four heterozygous substitutions, and it collectively contained about 72.22% of the G. anomalum genome. Twenty-four quantitative trait loci associated with plant height, yield, and fiber qualities were detected on 15 substitution segments. Integrating the reference genome with agronomic trait evaluation of the CSSLs enabled location and cloning of two G. anomalum genes that encode peroxiredoxin and putative callose synthase 8, respectively, conferring drought tolerance and improving fiber strength. We have demonstrated the power of a high-quality wild-species reference genome for identifying agronomically valuable alleles to facilitate interspecific introgression breeding in crops.