2011 Annual Report
1a.Objectives (from AD-416)
Objective 1: To characterize spatial, temporal, and/or genotypic variation in cotton fiber gene expression and the mechanisms leading to this variation to identify strategies for producing cotton fiber with enhanced or novel properties.
Objective 2: Determine the consequences of environmental factors on cotton fiber development and develop tools to mitigate these effects.
1b.Approach (from AD-416)
Determine global patterns of genetic differences and gene expression in genotypes that differ in fiber properties. Determine global patterns of gene expression in cotton ovule cultures that are induced to express secondary cell wall CesA genes prematurely. Validate transcription factor candidates by functional genomic approaches in model systems and cotton. Compare the gene expression profiles from controls and cotton plants undergoing heat and/or drought stresses. Determine the effects of heat units on fiber strength and expression of genes specifically involved in the transition period. Evaluate the effects of drought on the fiber quality in a group of varieties (germplasm lines).
Map cotton fiber quality traits and yield using recombinant inbred lines (RILs) derived from random mating. The 550 RILs derived from random mating of 11 cotton varieties demonstrated wide range of variations in fiber quality and yield. We analyzed 275 RILs with 770 microsatellite markers (one kind of DNA marker). These markers revealed more than 1,350 loci (genetic location on a chromosome) within the RILs tested, and covered 92% of the genome. The RILs were planted in Mississippi in 2009-2011 to collect yield and fiber data. Future work will be to identify DNA markers associated with fiber quality and yield traits, and use the markers to assist breeding.
Functionally characterize a putative gene controlling cotton fiber elongation. Ligon-lintless-2 (Li2) is a mutant that causes very short fiber. A DNA marker was found to perfectly associate with the Li2 phenotype in a population. The DNA regions around the Li2 locus in chromosome 18 were cloned and sequenced to identify the Li2 gene per se and the possibility of presence of other genes responsible for the phenotype. Two single nucleotide polymorphisms (SNPs) were identified in transcribed products between the Li2 mutant and wild type. Future work will be to analyze the association between the SNPs and Li2 phenotypes.
Clone cellulose synthase catalytic subunit 2 (CesA2) genes from cotton. CesA2 genes play a pivotal role in fiber development. A pair of genes encoding CesA2 were isolated by screening cotton bacterial artificial chromosome library. The genes encode 1,039 and 1,040 amino acids, respectively. Temporal and spatial regulations of the genes were compared between two cotton lines with different fiber strength. The cotton line with higher strength had higher gene expressions than the line with lower fiber strength during fiber development. This implies that both genes might contribute to cotton fiber properties such as fiber strength.
Effects of auxin on GhCesA4 responsible for cellulose biosynthesis in developing cotton fibers. GhCesA4 involves in cellulose production in cotton fiber. A synthetic auxin (plant hormone), 1-naphthaleneacetic acid (NAA) was able to decrease the expression of GhCesA4 in the in vitro cultured cotton fibers. The dose-dependent down-regulation of GhCesA4 expression by NAA was observed when fibers were cultured with NAA for either 4 weeks or 24 hours. Future work will be to determine how cellulose content and fiber elongation are affected by NAA during cotton fiber development.
Improve cotton fiber quality through interspecies crosses. Cotton hybrids were developed by a series of crosses and chromosome doubling using upland cotton SG747, Gossypium (G.) arboreum, G. herbaceum, and G. amourianum. Although G. amourianum is fiberless, it is a major contributor to fiber strength when introgressed into upland cotton resulting in an 80 to 146% increase in strength. Pollens from synthetic tetraploid hybrid plants were crossed with cotton variety SG747 plants in a greenhouse. F1 seeds from these crosses were planted in the field and fiber will be harvested and measured in the Fall 2011.
Ligon-lintless 2 (Li2) gene impairs fiber elongation, and results in lintless fiber. ARS scientists in the Cotton Fiber Bioscience Research Unit at New Orleans, LA, determined the genetic control and chromosomal location of Li2, a gene resulting in extremely short lint fibers (<6 mm). Li2 is a dominant gene and resides on chromosome 18. Five microsatellite markers (a kind of DNA marker) were identified as linked to Li2. Scanning electron microscopy analysis demonstrated that the mutant Li2 line not only initiates fuzz fibers but also initiates lint fibers. However, the elongation of lint fibers is impaired. Using the gene expression profiles, ARS scientists discovered an additional microsatellite marker that displayed complete linkage with the Li2 gene. This marker resided in a gene that may be the Li2 gene.
Accumulated heat units affected fiber bundle strength. Cotton fiber quality (length, strength, etc.) is greatly affected by environmental factors such as temperatures during growing season. ARS scientists in the Cotton Fiber Bioscience Research Unit at New Orleans, LA, observed that the fiber bundle-strength differences between two cotton near-isogenic (almost genetically identical) lines MD 52ne and MD 90ne were present as early as 20 days after flowering, and persisted to boll opening and fiber maturity. The accumulated heat units during the growing seasons affected the expression, regulation and function of genes that were related to fiber development. The onset of transition stage (one of several fiber development stages) was correlated with the accumulated heat units from the day of flowering in both cotton lines in all seasons. Higher accumulated heat units caused earlier entrance into the transition stage, and resulted in increased fiber bundle strength. This research suggests that the identification of genes associated with early entrance into the transition stage can be used to temporally manipulate fiber development and improve fiber quality.
Hinchliffe, D.J., Meredith Jr, W.R., Delhom, C.D., Thibodeaux, D.P., Fang, D.D. 2011. Elevated growing degree days influence transition stage timing during cotton (Gossypium hirsutum L.) fiber development and result in increased fiber strength. Crop Science. 51:1683-1692. DOI: 10.2135/cropsci2010.10.0569.
Naoumkina, M.A., Dixon, R. 2011. Characterization of the mannan synthase promoter from guar (Cyamopsis tetragonoloba). Plant Cell and Environment. (2011)30:997-1006.
Kim, H.J., Murai, N., Fang, D.D., Triplett, B.A. 2010. Functional analysis of Gossypium hirsutum cellulose synthase catalytic subunit 4 promoter in transgenic Arabidopsis and cotton tissues. Plant Science. 180(2011);323-332.