Roy G. Creech

Evaluation of genetic variances, heritabilities, and correlations for yield and fiber traits among cotton F2 hybrid populations

SummaryF2 hybrid cultivars continue to occupy a small portion of the cotton (Gossypium hirsutum L.) production are in the United States, but occupy a larger proportion of the production area in some other countries. Sixty-four F2 hybrids resulting from crosses of four commercial cultivars and 16 pest-resistant germplasm lines were evaluated for five fiber and four yield traits in four environments at Mississippi State, MS. An additive-dominance genetic model was employed for these traits. The minimum norm quadratic unbiased estimation (MINQUE) method was used with a mixed model approach for estimating genetic variance and covariance components and for predicting genetic correlations. This study investigated genetic variances, heritabilities, and genetic and phenotypic correlations between agronomic and fiber traits among these 64 F2 hybrid populations and discussed the usefulness of these populations for use as hybrids or for selections for pure lines.Dominance variance accounted for the major proportion of the phenotypic variances for lint yield, lint percentage, and boll size indicating that hybrids should have an advantage for these traits compared to pure lines. A low proportion of additive variance for fiber traits and the significant additive x environment variance components indicated a lack of substantial useful additive genetic variability for fiber traits. This suggests that selections for pure lines within these F2 populations would have limited success in improving fiber traits. Genetic and phenotypic correlation coefficients were of comparable magnitude for most pairs of characters. Fiber strength showed a positive additive genetic correlation with boll weight. Dominance genetic correlations of fiber strength with elongation and 2.5% span length were also significant and positive; however, the additive genetic correlation of length and strength was zero.

Differential expression of a lipid transfer protein gene in cotton fiber.

A full-length cDNA clone, GH3, has been isolated from a cotton fiber cDNA library using a differential screening method. The nucleotide and derived amino acid sequence data show that GH3 encodes a lipid transfer protein (LTP) of 120 amino acids. The presence of a transmembrane signal peptide at the N-terminal of the protein would suggest its possible outer cellular location in fiber cells. Northern analysis indicates that the GH3 gene is developmentally regulated.

Analysis of promoter activity of cotton lipid transfer protein gene LTP6 in transgenic tobacco plants

A cotton (Gossypium hirsutum) genomic clone (1.7-kb DNA insert) harboring the lipid transfer gene Ltp6 specifically expressed in fiber cells had been previously isolated and characterized. By using PCR amplification, the 447 bp Ltp6 promoter and a series of 5% deletions of the promoter were generated and cloned into a pBI101 plasmid upstream of the GUS (b-glucuronidase) reporter gene. These constructs were introduced into Agrobacterium tumefaciens LBA4404, and leaf disks of tobacco (Nicotiana tabacum L.) were transformed with A. tumefaciens LBA4404 carrying various promoter-GUS pBI101 plasmids. Histochemical analyses of the transgenic tobacco seedlings indicated that the Ltp6 promoter (from nt 447 to 1, undeleted) directed GUS expression only in trichomes (hair cells). Fluorometric GUS assays showed that the promoter activity of the undeleted Ltp6 promoter was at least 1000 times weaker than that of the 35S promoter of cauliflower mosaic virus (CaMV). Sequential deletions of the promoter gradually decreased the expression level of the GUS gene. No GUS activity was observed when the 5% deletion of the Ltp6 promoter reached to nt 86, which removed the putative CAAT and TATA promoter elements.

Cloning and characterization of a cotton lipid transfer protein gene specifically expressed in fiber cells

A cotton genomic library was screened using a fiber-specific cDNA (GH3) encoding a lipid transfer protein (LTP). One genomic clone (1.7 kb DNA insert) containing the Ltp gene (Ltp6) was sequenced and characterized. The Ltp6 contains an open reading frame of 360 bp, which is interrupted by a single intron (136 bp) located in the region corresponding to the C-terminal of the protein. The derived amino-acid sequence of LTP6 is 64% homologous to that of GH3. Like the GH3 gene, the Ltp6 is specifically expressed in fiber cells in a temporal manner. However, its expression level is lower than that of GH3.

Identification of resistance gene analogs in cotton (Gossypium hirsutum L.)

Sequence analyses of numerous plant disease resistance genes have revealed the presence of conserved motifs common to this class of genes, namely a nucleotide binding site (NBS) and leucine rich repeat region. In this study, thirty-three resistance gene analogs (RGAs) were cloned and sequenced from cotton (Gossypium hirsutum L.) following PCR with degenerate primers designed from the conserved NBS motif of plant resistance (R) genes. Phylogenetic analysis of the predicted amino acid sequences grouped the RGAs into four distinct classes from which several subgroups were delineated based on nucleic acid sequences. Gene database searches with the consensus protein sequences of each of the four classes and respective subgroups of cotton RGAs revealed their conserved NBS domains and homology to RGAs and known resistance genes from a variety of plant genera. Given the complete lack of knowledge regarding molecular organization of R genes in cotton, the cloned RGAs described here may be useful as probes to map, characterize, and manipulate R genes of the cotton genome.

Molecular cloning, differential expression, and functional characterization of a family of class I ubiquitin-conjugating enzyme (E2) genes in cotton (Gossypium)

Two cDNAs and their corresponding genes (GhUBC1 and GhUBC2) encoding ubiquitin-conjugating enzymes (E2s) have been cloned and characterized from allotetraploid cotton Gossypium hirsutum ((AD)(1) genome). Three additional E2 genes (GaUBC1, GtUBC2, and GrUBC2) have also been identified from diploid cottons Gossypium arboreum (A(2) genome), Gossypium thurberi (D(1) genome), and Gossypium raimondii (D(5) genome), respectively. The derived amino acid sequences of the five closely related cotton E2s are 77-79% identical to yeast ScUBC4 and ScUBC5. The GhUBC1/2 gene family is composed of two members, and genomic origin analysis indicates that GhUBC1 and 2 are individually present in the A and D subgenomes of G. hirsutum. The transcript levels of GhUBC1/2 increased significantly in leaves and flowers at senescence, suggesting that GhUBC1/2 may play a role in the degradation of target proteins that function in the delay of the senescence program. Correlated with high auxin content and auxin-associated effects, GhUBC1/2 are also highly expressed in the youngest leaves, the apical part of lateral roots, and elongating fibers. Genetic complementation experiments revealed that GhUBC1 and 2 can substitute for the function of ScUBC4 and 5 required for the selective degradation of abnormal and short-lived proteins in a yeast ubc4ubc5 double mutant.

A novel root-specific gene, MIC-3, with increased expression in nematode-resistant cotton (Gossypium hirsutum L.) after root-knot nematode infection ☆

A full-length cDNA, MIC-3, has been identified from a lambda ZAPII cDNA library constructed from the mRNA of nematode-resistant cotton (Gossypium hirsutum L.) roots after infection with root-knot nematode (Meloidogyne incognita). The putative open reading frame of MIC-3 encoded a protein of 141 amino acids with a calculated molecular mass of 15.3 kDa. Seven alternative polyadenylation sites have been identified for the MIC-3 transcripts, and the major transcripts are the longest ones. The MIC-3 gene contains a single intron within its coding region and belongs to a novel, multi-gene family containing up to six members. Expression of MIC-3 is root localized and specifically enhanced in the nematode induced, immature galls of resistant cotton line M-249, suggesting that MIC-3 may play a critical role in the resistance response to root-knot nematode.

Cloning and Expression Analysis of Two Cotton (Gossypium Hirsutum L.) Genes Encoding Cell Wall Proline-rich Proteins

Two cotton (Gossypium hirsutum L.) genes, ghprpl and ghprpl, encoding cell wall proline-rich proteins (PRPs) have been cloned and characterized. The ghprpl gene has an open reading frame (ORF) that encodes a PRP of 299 amino acids (aa), whereas the ghprp2 gene contains an ORF that codes for a 310-aa PRP. The GhPRPl has an 80% identity in aa sequence with that of GhPRP2. Like other plant cell wall PRPs, both cotton PRPs have a hydrophobic signal peptide at their N-termini, followed by repeating peptide units. Northern blot analyses showed that the ghprp1 gene is predominantly expressed in the fiber during the elongation stage of fiber development. Reverse transcription (RT)-PCR analysis showed that ghprp1 is expressed in both fiber and root tissues, whereas ghprpl is in roots only. The ghprp1 gene was shown to be present in the A1, A2, D1 and D5 genomes of Gossypium by PCR amplification, whereas the ghprpl gene is only present in the A1 and A2 genomes. The ghprp1 gene was over-expressed in the yeast Pichia pastoris, and the expressed GhPRP1 protein was used as an antigen to raise polyclonal antibodies (anti-GhPRP1). Western analysis using the anti-GhPRP1 probe detected a major protein band (50 kDa) in 5-31-day postanthesis (DPA) fibers. However, the 50 kDa protein was absent in other cotton tissues.

Nematode Resistance in Cotton

Nematode parasitism of cotton, has become increasingly important due to yield losses and increased distribution across cotton production regions. Yield losses attributed to nematodes in 1991 in the 14 cotton-producing states in the USA were estimated to be approximately 2.4%, or in excess of 476151 bales (Smith 1992). In 1992, plant-parasitic nematodes accounted for an estimated yield loss of 528000 bales valued at US

Cloning and promoter analysis of the cotton lipid transfer protein gene Ltp3.

184951200 (Goodell 1993). The Cotton Disease Council reported yield losses in 1995 in Mississippi at about 4% or 82929 bales, and beltwide in the USA about 3.5%, or about 778703 bales. Decreases in fiber length and other adverse affects on fiber quality due to nematode infection were reported by Smith et al. (1991).