Project description:Cotton fiber were used for the expression analysis at different developmental stages Affymetrix Cotton Genome array were used for the global profiling of gene expression of cotton fiber at different developmental stages
Project description:Cotton bacterial blight (CBB), an important disease of (Gossypium hirsutum) in the early 20th century, had been controlled by resistant germplasm for over half a century. Recently, CBB re-emerged as an agronomic problem in the United States. Analysis of cotton variety planting statistics indicates a steady increase in the percentage of susceptible cotton varieties grown each year since 2009. Phylogenetic analysis revealed that strains from the current outbreak cluster with race 18 Xanthomonas citri pv. malvacearum (Xcm) strains. Illumina based draft genomes were generated for thirteen Xcm isolates. These genomes, along with 4 previously published Xcm genomes, encode 24 conserved and nine variable type three effectors. Strains in the race 18 clade contain 3 to 5 more effectors than other Xcm strains. SMRT sequencing of two geographically and temporally diverse strains of Xcm yielded circular chromosomes and accompanying plasmids. These genomes encode eight and thirteen distinct transcription activator-like effector genes. RNA-sequencing revealed 52 genes induced within two cotton cultivars by both tested Xcm strains. This gene list includes a homeologous pair of genes, with homology to the known susceptibility gene, MLO. In contrast, the two strains of Xcm induce different class III SWEET sugar transporters. Subsequent genome wide analysis revealed patterns in the overall expression of homeologous gene pairs in cotton after inoculation by Xcm. These data reveal host-pathogen specificity at the genetic level and strategies for future development of resistant cultivars.
Project description:Cotton fibers are seed trichomes, and their development undergoes a series of rapid and dynamic changes from fiber cell initiation, elongation to primary and secondary wall biosynthesis and fiber maturation. Previous studies showed that cotton homologues encoding putative MYB transcription factors and phytohormone responsive factors were induced during early stages of ovule and fiber development. Many of these factors are targets of microRNAs (miRNAs). miRNAs are ~21 nucleotide (nt) RNA molecules derived from non-coding endogenous genes and mediate target regulation by mRNA degradation or translational repression. Here we show that among ~4-million reads of small RNAs derived from the fiber and non-fiber tissues, the 24-nt small RNAs were most abundant and were highly enriched in ovules and fiber-bearing ovules relative to leaves. A total of 28 putative miRNAs families, including 25 conserved and 3 novel miRNAs were identified in at least one of the cotton tissues examined. Thirty-two pre-miRNA hairpins representing 19 unique families were detected in Cotton Gene Indices version 9 (CGI9) using mirCheck. Sequencing, miRNA microarray, and small RNA blot analyses showed that many of these miRNAs differentially accumulated during ovule and fiber development. The cotton miRNAs examined triggered target cleavage in the same predicted sites of the cotton targets in ovules and fibers as that of the orthologous target genes in Arabidopsis. Targets of the potential new cotton miRNAs matched the previously characterized ESTs derived from cotton ovules and fibers. The miRNA targets including those encoding auxin response factors were differentially expressed during fiber development. We suggest that both conserved and new miRNAs play an important role in the rapid and dynamic process of fiber and ovule development in cotton.
Project description:exceptional example of evolutionary innovation is the single-celled seed trichome in Gossypium ("cotton fiber"). We have used fiber development in Gossypium as a system to understand how morphology can rapidly evolve. Fiber has undergone considerable morphological changes between the short, tightly adherent fibers of G. longicalyx and the derived long, spinable fibers of its closest relative, G. herbaceum, that facilitated cotton domestication. We conducted comparative gene expression profiling across a developmental time-course of fibers from G. longicalyx and G. herbaceum using microarrays with ~ 22,000 genes. Expression changes between stages were temporally protracted in G. herbaceum relative to G. longicalyx, reflecting a prolongation of the ancestral developmental program. Gene expression and GO analyses showed that many genes involved with stress responses were up-regulated early in G. longicalyx fiber development. Several candidate genes up-regulated in G. herbaceum have been implicated in regulating redox levels and cell elongation processes. Three genes previously shown to modulate hydrogen peroxide levels were consistently expressed in domesticated and wild cotton species with long fibers but expression was not detected by qRT-PCR in wild species with short fibers. Hydrogen peroxide is important for cell elongation, but at high concentrations it becomes toxic, activating stress processes that may lead to early onset of secondary cell wall synthesis and the end of cell elongation. These observations suggest that the evolution of long spinable fibers in cotton was accompanied by novel expression of genes assisting in the regulation of reactive oxygen species levels. Our data suggest a model for the evolutionary origin of a novel morphology through differential gene regulation causing prolongation of an ancestral developmental program. Keywords: Cotton, fiber, evolution, time-point, comparative genomic hybridization, stress response genes, H2O2