[Biological characters of Bemisia tabaci (Gennadius) experimental population on cotton varieties in Xinjiang]

The development, survival, reproduction, and life-span of Bemisia tabaci (Gennadius) on six major cotton varieties (Xinluzao 8, Xinluzao 16, Xinluzao 17, Zhongmian 35, Kang 5, and Dai 80) in Xinjiang were studied under the conditions of (26 +/- 1) degrees C, relative humidity (75 +/- 1)%, and illumination L:D = 16:8 in laboratory. The life table of the B. tabaci experimental population was established, and the population net reproductive rate (R0), intrinsic rate of increase (rm), mean generation time (T), and finite growth rate (A) were estimated. Significant differences were observed in the size, development duration, survival, and fecundity of the experimental population on the six cotton varieties. The fecundity and survival rate of B. tabaci were the highest on Xinluzao 16 and the lowest on Kang 5. Xinluzao 16 was the most appropriate host for the growth and development of B. tabaci population, followed by Zhongmian 35, while Kang 5 was the most unsuitable host.

QTL mapping for plant architecture traits in upland cotton using RILs and SSR markers

Xiangzamian 2 (XZM2) is the most widely cultivated cotton hybrid in China. By crossing two parents Zhongmiansuo12 and 8891 and upon subsequent selfings, we got F8 and F9 populations having 180 recombinant inbred lines. Ten plant architecture traits were investigated in two years with this population. A genetic map was constructed mainly with SSR markers. Quantitative trait loci (QTL) conditioning plant architecture traits were determined at the single-locus and double-locus levels. The results showed that epistastic effects as well as additive effects of QTL played an important role as the genetic basis of cotton plant architecture. The QTL detected in our research might provide new information on improving plant architecture traits. The polymorphism of molecular markers between ZMS12 and 8891 were quite limited, while significant differences between their phenotypes were found and the hybrid XZM2 expressed high heterosis in yield. All these could be partly explained by the effect of epistatic QTL.

Molecular diversity and association mapping of fiber quality traits in exotic G. hirsutum L. germplasm

The narrow genetic base of cultivated cotton germplasm is hindering the cotton productivity worldwide. Although potential genetic diversity exists in Gossypium genus, it is largely 'underutilized' due to photoperiodism and the lack of innovative tools to overcome such challenges. The application of linkage disequilibrium (LD)-based association mapping is an alternative powerful molecular tool to dissect and exploit the natural genetic diversity conserved within cotton germplasm collections, greatly accelerating still 'lagging' cotton marker-assisted selection (MAS) programs. However, the extent of genome-wide linkage disequilibrium (LD) has not been determined in cotton. We report the extent of genome-wide LD and association mapping of fiber quality traits by using a 95 core set of microsatellite markers in a total of 285 exotic Gossypium hirsutum accessions, comprising of 208 landrace stocks and 77 photoperiodic variety accessions. We demonstrated the existence of useful genetic diversity within exotic cotton germplasm. In this germplasm set, 11-12% of SSR loci pairs revealed a significant LD. At the significance threshold (r(2)>/=0.1), a genome-wide average of LD declines within the genetic distance at <10 cM in the landrace stocks germplasm and >30 cM in variety germplasm. Genome wide LD at r(2)>/=0.2 was reduced on average to approximately 1-2 cM in the landrace stock germplasm and 6-8 cM in variety germplasm, providing evidence of the potential for association mapping of agronomically important traits in cotton. We observed significant population structure and relatedness in assayed germplasm. Consequently, the application of the mixed liner model (MLM), considering both kinship (K) and population structure (Q) detected between 6% and 13% of SSR markers associated with the main fiber quality traits in cotton. Our results highlight for the first time the feasibility and potential of association mapping, with consideration of the population structure and stratification existing in cotton germplasm resources. The number of SSR markers associated with fiber quality traits in diverse cotton germplasm, which broadly covered many historical meiotic events, should be useful to effectively exploit potentially new genetic variation by using MAS programs.

[Protein markers for identification of different species and varieties of cotton]

Reference electrophoretic spectra that allow compiling electrophoretic formulas of certain cotton species and varieties were obtained on the basis of analysis of the electrophoretic spectrum of water-soluble and barely soluble proteins of seeds of diploid cotton species of genomic group A (Gossypium arboretum var. indicum, G. arboreum ssp. obtusifolum, G. herbaceum ssp. africanum, and G. herbaceum Harga), group C (G. australe, G. bickii, G. nelsone, and G. sturtianum), group D (G. davidsonii. G. harknessii. G. klotzschianum, G. raimondii, G. thurberi, and G. trilobum), and amphidiploid species of group AD (G. mustelinum, G. hirsutum ssp. palmeri, G. tricuspidatum Bagota, G. tricuspidatum Mari Galanta, G. barbadense L., and G. hirsutum L.).

Molecular cloning, expression profiling, and yeast complementation of 19 beta-tubulin cDNAs from developing cotton ovules

Microtubules are a major structural component of the cytoskeleton and participate in cell division, intracellular transport, and cell morphogenesis. In the present study, 795 cotton tubulin expressed sequence tags were analysed and 19 beta-tubulin genes (TUB) cloned from a cotton cDNA library. Among the group, 12 cotton TUBs (GhTUBs) are reported for the first time here. Transcription profiling revealed that nine GhTUBs were highly expressed in elongating fibre cells as compared with fuzzless-lintless mutant ovules. Treating cultured wild-type cotton ovules with exogenous phytohormones showed that individual genes can be induced by different agents. Gibberellin induced expression of GhTUB1 and GhTUB3, ethylene induced expression of GhTUB5, GhTUB9, and GhTUB12, brassinosteroids induced expression of GhTUB1, GhTUB3, GhTUB9, and GhTUB12, and lignoceric acid induced expression of GhTUB1, GhTUB3, and GhTUB12. When GhTUBs were transformed into the Saccharomyces cerevisiae inviable mutant, tub2, which is deficient in beta-tubulin, one ovule-specific and eight of nine fibre-preferential GhTUBs rescued this lethality. This study suggests that the proteins encoded by cotton GhTUBs are involved during cotton fibre development.

Meta-analysis of polyploid cotton QTL shows unequal contributions of subgenomes to a complex network of genes and gene clusters implicated in lint fiber development

QTL mapping experiments yield heterogeneous results due to the use of different genotypes, environments, and sampling variation. Compilation of QTL mapping results yields a more complete picture of the genetic control of a trait and reveals patterns in organization of trait variation. A total of 432 QTL mapped in one diploid and 10 tetraploid interspecific cotton populations were aligned using a reference map and depicted in a CMap resource. Early demonstrations that genes from the non-fiber-producing diploid ancestor contribute to tetraploid lint fiber genetics gain further support from multiple populations and environments and advanced-generation studies detecting QTL of small phenotypic effect. Both tetraploid subgenomes contribute QTL at largely non-homeologous locations, suggesting divergent selection acting on many corresponding genes before and/or after polyploid formation. QTL correspondence across studies was only modest, suggesting that additional QTL for the target traits remain to be discovered. Crosses between closely-related genotypes differing by single-gene mutants yield profoundly different QTL landscapes, suggesting that fiber variation involves a complex network of interacting genes. Members of the lint fiber development network appear clustered, with cluster members showing heterogeneous phenotypic effects. Meta-analysis linked to synteny-based and expression-based information provides clues about specific genes and families involved in QTL networks.

Detection methods for biotech cotton MON 15985 and MON 88913 by PCR

Plants derived through agricultural biotechnology, or genetically modified organisms (GMOs), may affect human health and ecological environment. A living GMO is also called a living modified organism (LMO). Biotech cotton is a GMO in food or feed and also an LMO in the environment. Recently, two varieties of biotech cotton, MON 15985 and MON 88913, were developed by Monsanto Co. The detection method is an essential element for the GMO labeling system or LMO management of biotech plants. In this paper, two primer pairs and probes were designed for specific amplification of 116 and 120 bp PCR products from MON 15985 and MON 88913, respectively, with no amplification from any other biotech cotton. Limits of detection of the qualitative method were all 0.05% for MON 15985 and MON 88913. The quantitative method was developed using a TaqMan real-time PCR. A synthetic plasmid, as a reference molecule, was constructed from a taxon-specific DNA sequence of cotton and two construct-specific DNA sequences of MON 15985 and MON 88913. The quantitative method was validated using six samples that contained levels of biotech cotton mixed with conventional cotton ranging from 0.1 to 10.0%. As a result, the biases from the true value and the relative deviations were all within the range of +/-20%. Limits of quantitation of the quantitative method were all 0.1%. Consequently, it is reported that the proposed detection methods were applicable for qualitative and quantitative analyses for biotech cotton MON 15985 and MON 88913.

The role of induced mutation in conversion of photoperiod dependence in cotton

Wild cotton germplasm resources are largely underutilized because of photoperiod-dependent flowering of "exotic" cottons. The objectives of this work were to explore the genome-wide effect of induced mutation in photoperiod-converted induced cotton mutants, estimating the genetic change between mutant and wild-type cottons using simple sequence repeats (SSRs) as well as understand the pattern of SSR mutation in induced mutagenesis. Three groups of photoperiod-converted radiomutants ((32)P) including their wild-type parental lines, A- and D-genome diploids, and typically grown cotton cultivars were screened with 250 cotton SSR primer pairs. Forty SSRs revealed the same SSR mutation profile in, at least, 2 independent mutant lines that were different from the original wild types. Induced mutagenesis both increased and decreased the allele sizes of SSRs in mutants with the higher mutation rate in SSRs containing dinucleotide motifs. Genetic distance obtained based on 141 informative SSR alleles ranged from 0.09 to 0.60 in all studied cotton genotypes. Genetic distance within all photoperiod-converted induced mutants was in a 0.09-0.25 range. The genetic distance among photoperiod-converted mutants and their originals ranged from 0.28 to 0.50, revealing significant modification of mutants from their original wild types. Typical Gossypium hirsutum cultivar, Namangan-77, revealed mutational pattern similar to induced radiomutants in 40 mutated SSR loci, implying possible pressure to these SSR loci not only in radiomutagenesis but also during common breeding process. Outcomes of the research should be useful in understanding the photoperiod-related mutations, and markers might help in mapping photoperiodic flowering genes in cotton.

Circumvention of over-excitation of PSII by maintaining electron transport rate in leaves of four cotton genotypes developed under long-term drought

We investigated the patterns of response to a long-term drought in the field in cotton cultivars (genotypes) with known differences in their drought tolerance. Four cotton genotypes with varying physiological and morphological traits, suited to different cropping conditions, were grown in the field and subjected to a long-term moderate drought. In general, cotton leaves developed under drought had significantly higher area-based leaf nitrogen content (N (area)) than those under well irrigation. Droughted plants showed a lower light-saturated net photosynthetic rate (A (sat)) with lower stomatal conductance (g (s)) and intercellular CO (2) concentration (C (i)) than irrigated ones. Based on the responses of A (sat) to g (s) and C (i), there was no decreasing trend in A (sat) at a given g (s) and C (i) in droughted leaves, suggesting that the decline in A (sat) in field-grown cotton plants under a long-term drought can be attributed mainly to stomatal closure, but not to nonstomatal limitations. There was little evidence of an increase in thermal energy dissipation as indicated by the lack of a decrease in the photochemical efficiency of open PSII (F (v)'/F (m)') in droughted plants. On the basis of electron transport (ETR) and photochemical quenching (q (P)), however, we found evidence indicating that droughted cotton plants can circumvent the risk of excessive excitation energy in photosystem (PS) II by maintaining higher electron transport rates associated with higher N (area), even while photosynthetic rates were reduced by stomatal closure.

Somatic embryogenesis and plant regeneration from different wild diploid cotton (Gossypium) species

Calli were successfully induced from hypocotyls of eight wild diploid cotton species (Gossypium) on MSB (MS salts and B(5) vitamins) medium supplemented with 0.09 microM 2,4-D (2,4-dichlorophenoxyacetic acid) and 2.32 microM KT (kinetin). Plant growth regulator (PGR) combinations, adding GA(3) (Gibberellic acid), high inorganic salt stress, and PGR-free media were used to induce embryogenic calli from nonembryogenic calli. Embryogenic cultures were induced from G. aridum S. (D(4) genome), G. davidsonii K. (D(3)-d genome), G. klotzschianum A. (D(3)-k genome), G. raimondii U. (D(5) genome), and G. stocksii M. (E(1) genome). We then observed somatic embryogenesis in the five species while calli of G. africanum V. (A(1)-2 genome), G. anomalum W. (B(1) genome), and G. bickii P. (G genome) remained nonembryogenic. Somatic embryogenesis was adjusted by changing sugar sources, regulating combinations of PGRs, and using cell suspension culture. Embryos at various developmental stages produced mature and germinating embryos when cultured on filter paper placed on the media containing different sugar sources. The utility of different sugar sources promoted globular embryos developing into cotyledonary stage and increased the frequency of cotyledonary embryos developing into normal plants. Normal plantlets were regenerated from G. davidsonii, G. klotzschianum, G. raimondii, and G. stocksii. Only abnormal plantlets were obtained in G. aridum. This work will contribute to broadening the number of regenerable cotton species and provide foundations for somatic hybridization in cotton to create new germplasm.

The complete chloroplast genome sequence of Gossypium hirsutum: organization and phylogenetic relationships to other angiosperms

BACKGROUND

Cotton (Gossypium hirsutum) is the most important fiber crop grown in 90 countries. In 2004-2005, US farmers planted 79% of the 5.7-million hectares of nuclear transgenic cotton. Unfortunately, genetically modified cotton has the potential to hybridize with other cultivated and wild relatives, resulting in geographical restrictions to cultivation. However, chloroplast genetic engineering offers the possibility of containment because of maternal inheritance of transgenes. The complete chloroplast genome of cotton provides essential information required for genetic engineering. In addition, the sequence data were used to assess phylogenetic relationships among the major clades of rosids using cotton and 25 other completely sequenced angiosperm chloroplast genomes.

RESULTS

The complete cotton chloroplast genome is 160,301 bp in length, with 112 unique genes and 19 duplicated genes within the IR, containing a total of 131 genes. There are four ribosomal RNAs, 30 distinct tRNA genes and 17 intron-containing genes. The gene order in cotton is identical to that of tobacco but lacks rpl22 and infA. There are 30 direct and 24 inverted repeats 30 bp or longer with a sequence identity > or = 90%. Most of the direct repeats are within intergenic spacer regions, introns and a 72 bp-long direct repeat is within the psaA and psaB genes. Comparison of protein coding sequences with expressed sequence tags (ESTs) revealed nucleotide substitutions resulting in amino acid changes in ndhC, rpl23, rpl20, rps3 and clpP. Phylogenetic analysis of a data set including 61 protein-coding genes using both maximum likelihood and maximum parsimony were performed for 28 taxa, including cotton and five other angiosperm chloroplast genomes that were not included in any previous phylogenies.

CONCLUSION

Cotton chloroplast genome lacks rpl22 and infA and contains a number of dispersed direct and inverted repeats. RNA editing resulted in amino acid changes with significant impact on their hydropathy. Phylogenetic analysis provides strong support for the position of cotton in the Malvales in the eurosids II clade sister to Arabidopsis in the Brassicales. Furthermore, there is strong support for the placement of the Myrtales sister to the eurosid I clade, although expanded taxon sampling is needed to further test this relationship.

[Studies on the cytological characters of the interspecific hybrid F1 among the cultivated species in Gossypium and their genetic relationship]

Interspescific hybridization among four cultivated species in Gossypium (G. herbaceum, G. arboreum, G. hirsutum and G. barbadense) were carried out to produce dispecific hybrids F1, (G. arboreum x G. herbaceum) F1 and (G. hirsutum x G. barbadense) F1, and quadrispecific hybrid F1, which was produced by crossed the chromosome doubled (G. arboreum x G. herbaceum) F1 with (G. hirsutum x G. barbadense) F1. In order to study the evolution relationship among the four cultivated species in Gossypium, the characteristic of chromosome behavior during the meiosis and pollen viability in those interspecific hybrids F1 were studied in this paper. The results showed that the diploid interspecific hybrid, (G. arboreum x G. herbaceum) F1, had a four-chromosome-ring, the chromosome configuration was 2n = 26 = 11 II + 1 IV. And the normal pollen percent was 50.71%, which showed the character of typical gamete semi-sterility, and approved that there was a chromosome translocation between the two diploid cotton species, G. arboreum and G. herbaceum. For the allotetraploid species interspecific hybrid F1, (G. hirsutum x G. barbadense) F1, most of the chromosomes at metaphase I could be paired into bivalents, with a few number of univalents, trivalents, and quardrivalents. The chromosome configuration was 2n = 52 = 0.78 I +22.24 II +0.94 III +0.98 IV, with a normal pollen rate of 54. 84%. The experiment showed that there were a few chromosome translocation or chromosome inversion between the two allotetraploid cotton species, G. hirsutum and G. barbadenses. The meiosis of the quardrispecific hybrid F1 was abnormal, and the loss of chromosomes was common. Most of the chromosomes could not synapse at metaphase I, which led to many univalents and some multivalents. The chromosome configuration of the quardrispecific hybrid F1 was 2n = 52 = 5.45 I +14.41 II +2.44 III +1.59 IV +0.63 V +0.15 VI, and the normal pollen rate was 6.87%, which showed that the relationship of four cultivated cotton species was relatively closed. It is possible to produce a new germplasm with the good characters of the four cultivated species through genetic recombination.

Incongruent patterns of local and global genome size evolution in cotton

Genome sizes in plants vary over several orders of magnitude, reflecting a combination of differentially acting local and global forces such as biases in indel accumulation and transposable element proliferation or removal. To gain insight into the relative role of these and other forces, approximately 105 kb of contiguous sequence surrounding the cellulose synthase gene CesA1 was compared for the two coresident genomes (AT and DT) of the allopolyploid cotton species, Gossypium hirsutum. These two genomes differ approximately twofold in size, having diverged from a common ancestor approximately 5-10 million years ago (Mya) and been reunited in the same nucleus at the time of polyploid formation, approximately 1-2 Mya. Gene content, order, and spacing are largely conserved between the two genomes, although a few transposable elements and a single cpDNA fragment distinguish the two homoeologs. Sequence conservation is high in both intergenic and genic regions, with 14 conserved genes detected in both genomes yielding a density of 1 gene every 7.5 kb. In contrast to the twofold overall difference in DNA content, no disparity in size was observed for this 105-kb region, and 555 indels were detected that distinguish the two homoeologous BACs, approximately equally distributed between AT and DT in number and aggregate size. The data demonstrate that genome size evolution at this phylogenetic scale is not primarily caused by mechanisms that operate uniformly across different genomic regions and components; instead, the twofold overall difference in DNA content must reflect locally operating forces between gene islands or in largely gene-free regions.

[Response of parasitic wasps of cotton bollworm to different cotton varieties with transgenic Bacillus thringienthsis genes]

The relationship between the parasitic wasp population number of cotton bollworm (Helicoverpa armigera) and the varieties of cotton was studied by releasing and collecting the eggs and larvae of cotton bollworm on transgenic and non-transgenic cottons. The research results from 2000 to 2003 showed that the parasitic rates of the eggs and larvae of cotton bollworm were notably lower in transgenic cotton field than in non-transgenic cotton field. At the same time, the effect of transgenic and non-transgenic cottons on the selection behavior of the parasitic wasp Microplitis mediatar of the larvae of cotton bollworm was studied by using "Y" olfactometer. The results showed that the selection response about the parasitic wasp Microplitis mediatar of cotton bollworm on non-transgenic cotton was prior to the transgenic cotton.

[Genetic diversity analysis of brown cotton and green cotton]

Genetic diversity analysis of brown cotton Xincai 1 and Xincai 2 and green cotton Xincai 3 and Xincai 4 and other 47 color cottons was conducted by the random amplified polymorphism DNA (RAPD) techniques, using 6 random primers. Cluster and similarity analysis of these cottons showed that the differences in genetic relationship and similarity among the brown cottons, green cottons and brown-green cottons are not remarkable. The results also reflect that the genetic bases of the brown and green cottons are narrow, and they are at the same genetic diversity level. These results are probably due to the same basic germplasms, the same breeding aims and the similar breeding approaches.

[An analysis about genetic basis of cotton cultivars in China since 1949 with molecular markers]

The diversity of 166 cotton cultivars(cult.) including 159 upland(G. hirsutum L) and 7 island(G. barbadense L) ones planted mainly in China since 1949 was explored by RAPD, genetic distance(GD) and cluster analysis. The correlation coefficients between Nei's GD of RAPDs and two groups of phenotype data's Euclidean distances (UD) were 0.6445(n = 1770) and 0.7078 (n = 7140), which indicated that RAPD could be used to explore genetic diversity among cotton cultivars in China. The genetic basis of cotton cultivars in China was studied by comparison among different cotton species, different cultivar types, different history periods, different growing regions and different sources. The results showed as follows:within cotton cultivars planted in China, the genetic basis of island cotton cultivars was narrower than that in upland ones; the genetic basis of cultivars released in China since 1949 was narrower than that of introduced ones from outside of China; the genetic basis of hybrids was narrower than that of conventional cultivars(Conv. Cult.); the genetic basis of upland cultivars after 1980 was narrower than that in 1970's; the genetic basis of cultivars in Changjiang cotton region was narrower than that of Huanghuai cotton region, northwestward cotton region was the narrowest. From which some strategies for breeding, especially for the methods of widening the genetic basis of China cotton cultivars, could be understood and withdrawn.

Differential evolutionary dynamics of duplicated paralogous Adh loci in allotetraploid cotton (Gossypium)

Levels and patterns of nucleotide diversity vary widely among lineages. Because allopolyploid species contain duplicated (homoeologous) genes, studies of nucleotide diversity at homoeologous loci may facilitate insight into the evolutionary dynamics of duplicated loci. In this study, we describe patterns of sequence diversity from an alcohol dehydrogenase homoeologous locus pair (AdhC) in allotetraploid cotton (Gossypium, Malvaceae). These data are compared with equivalent information from another homoeologous alcohol dehydrogenase gene pair (AdhA, Small, Ryburn, and Wendel 1999. Mol. Biol. Evol. 16:491-501) which has an overall slower evolutionary rate than AdhC. As expected from the predicted correlation between nucleotide diversity and evolutionary rate, nucleotide diversity was higher for AdhC than for AdhA. In addition, nucleotide diversity is higher in the D-subgenome of allotetraploid cotton for AdhC, confirming earlier observations for AdhA. These observations indicate that for these two pairs of Adh loci, the null hypothesis of equivalent evolutionary dynamics for duplicated genes in allotetraploid cotton is rejected.

Comparative development of fiber in wild and cultivated cotton

One of the most striking examples of plant hairs is the single-celled epidermal seed trichome of cultivated cotton. The developmental morphology of these commercial "fibers" has been well-characterized in Gossypium hirsutum, but little is known about the pattern and tempo of fiber development in wild Gossypium species, all of which have short, agronomically inferior fiber. To identify developmental differences that account for variation in fiber length, and to place these differences in a phylogenetic context, we conducted SEM studies of ovules at and near the time of flowering, and generated growth curves for cultivated and wild diploid and tetraploid species. Trichome initiation was found to be similar in all taxa, with few notable differences in trichome density or early growth. Developmental profiles of the fibers of most wild species are similar, with fiber elongation terminating at about two weeks post-anthesis. In contrast, growth is extended to three weeks in the A- and F-genome diploids. This prolonged elongation period is diagnosed as a key evolutionary event in the origin of long fiber. A second evolutionary innovation is that absolute growth rate is higher in species with long fibers. Domestication of species is associated with a further prolongation of elongation at both the diploid and allopolyploid levels, suggesting the effects of parallel artificial selection. Comparative analysis of fiber growth curves lends developmental support to previous quantitative genetic suggestions that genes for fiber "improvement" in tetraploid cotton were contributed by the agronomically inferior D-genome diploid parent.

Differential regulation of six novel MYB-domain genes defines two distinct expression patterns in allotetraploid cotton (Gossypium hirsutum L.)

A PCR-based strategy was employed to identify myb-related genes potentially involved in the differentiation and development of cotton seed trichomes. cDNA clones representing six newly identified cotton myb-domain genes (GhMYB) of the R2R3-MYB family were characterized in the allotetraploid species Gossypium hirsutum L. (2n = 4x = 52; AADD). Several interesting motifs and domains in the transregulatory region (TRR) were identified as potential candidates for modulating GhMYB activity. One such structural feature is a basic 40-amino acid stretch (TRR1) located immediately downstream of the DNA-binding domain (DBD) in five of the GhMYBs. Furthermore, the conserved motif GIDxxH identified in a subset of plant MYBs is also present in the same position in the TRR1 domains of GhMYB1 and GhMYB6, exactly 12 amino acid residues downstream of the last tryptophan in the R3 repeat of the DBD. At least two of the GhMYBs (GhMYB4 and GhMYB5) contain unidentified ORFS in the 5' leader sequence (5'-uORFs) that may serve to regulate the synthesis of these particular GhMYB proteins at the translational level. Multiple alignment of DBD sequences indicated that GhMYBs show structural similarity to plant R2R3-MYB factors implicated in phenylpropanoid biosynthesis. GhMYB5 is the most distantly related cotton R2R3-MYB and is found in an isolated cluster that includes the drought-inducible AtMYB2. Sequence comparisons of DBD and TRR domains from GhMYBs, MIXTA (AmMYBMx) and G11 (AtMYBG11) did not reveal any striking similarity beyond conserved motifs. However, based on earlier phylogenetic analysis, GhMYB2, GhMYB3, and GHMYB4 are members of a cluster that contains GLABROUS1, while GhMYB1 and GhMYB6 belong to a closely related cluster. Semi-quantitative RT-PCR analysis revealed two discrete patterns of GhMYB gene expression. Type I cotton MYB (GhMYB-1, -2, and -3) transcripts were found in all tissue-types examined and were relatively more abundant than those derived from type II GhMYB genes (GhMYB-4, -5, and -6), which showed distinct, tissue-specific expression patterns. The developmental regulation of GhMYBs is consistent with a role for these DNA-binding factors in the differentiation and expansion of cotton seed trichomes.

Bidirectional interlocus concerted evolution following allopolyploid speciation in cotton (Gossypium)

Polyploidy is a prominent process in plant evolution; yet few data address the question of whether homeologous sequences evolve independently subsequent to polyploidization. We report on ribosomal DNA (rDNA) evolution in five allopolyploid (AD genome) species of cotton (Gossypium) and species representing their diploid progenitors (A genome, D genome). Sequence data from the internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S gene indicate that rDNA arrays are homogeneous, or nearly so, in all diploids and allopolyploids examined. Because these arrays occur at four chromosomal loci in allopolyploid cotton, two in each subgenome, repeats from different arrays must have become homogenized by interlocus concerted evolution. Southern hybridization analysis combined with copy-number estimation demonstrate that this process has gone to completion in the diploids and to completion or near-completion in all allopolyploid species and that it most likely involves the entire rDNA repeat. Phylogenetic analysis demonstrates that interlocus concerted evolution has been bidirectional in allopolyploid species--i.e., rDNA from four polyploid lineages has been homogenized to a D genome repeat type, whereas sequences from Gossypium mustelinum have concerted to an A genome repeat type. Although little is known regarding the functional significance of interlocus concerted evolution of homeologous sequences, this study demonstrates that the process occurs for tandemly repeated sequences in diploid and polyploid plants. That interlocus concerted evolution can occur bidirectionally subsequent to hybidization and polyploidization has significant implications for phylogeny reconstruction, especially when based on rDNA sequences.

Acute bronchoconstriction induced by cotton dust: dose-related responses to endotoxin and other dust factors

Fifty-four healthy humans, selected for their acute airway responsiveness to cotton dust, had spirometric tests immediately before and after 6 hours of exposure to card-generated cotton dust from seven different cottons (of several grades and growing regions). During exposures, we measured airborne concentrations of viable fungi and bacteria (total and gram negative), vertically elutriated gravimetric dust, and vertically elutriated endotoxin. Correlation between each of these five exposure indices and exposure-related acute changes in forced expiratory volume in 1 s showed a statistically significant relationship between all of the indices except concentration of viable fungi. Of the other four indices, endotoxin was the most highly correlated (r = -0.94; p less than 0.00001), and gravimetric dust was the least correlated (r = -0.34; p less than 0.05). These findings suggest that gram-negative endotoxin may play a major role in the acute pulmonary response to inhaled cotton dust.