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Roots are involved in acquisition of water and nutrients, as well as in providing structural support to plant. The root system provides a dynamic model for developmental analysis. Here, we investigated quantitative trait loci (QTL), dynamic conditional QTL and epistatic interactions for seedling root traits using an upland cotton F2 population and a constructed genetic map. Totally, 37 QTLs for root traits, 35 dynamic conditional QTLs based on the net increased amount of root traits (root tips, forks, length, surface area and volume) (i) after transplanting 10 days compared to 5 days, and (ii) after transplanting 15 days to 10 days were detected. Obvious dynamic characteristic of QTL and dynamic conditional QTL existed at different developmental stages of root because QTL and dynamic conditional QTL had not been detected simultaneously. We further confirmed that additive and dominance effects of QTL qRSA-chr1-1 in interval time 5 to 10 DAT (days after transplant) offset the effects in 10 to 15 DAT. Lots of two-locus interactions for root traits were identified unconditionally or dynamically, and a few epistatic interactions were only detected simultaneously in interval time of 5-10 DAT and 10-15 DAT, suggesting different interactive genetic mechanisms on root development at different stages. Dynamic conditional QTL and epistasis effects provide new attempts to understand the dynamics of roots and provide clues for root architecture selection in upland cotton. [ABSTRACT FROM AUTHOR]

Construction of single chromosomal DNA libraries by chromosome micromanipulation is a useful tool for pursuing genomic studies. Thus far, micromanipulation in cotton has not been reported yet, which may be due to difficulty in preparing chromosomes of similar sizes. In this study, single chromosome micromanipulation was successfully achieved in cotton. A single chromosome 5 of Gossypium arboreum (cultivar Shixiya-1) carrying a large satellite at mitotic metaphase was isolated by microdissection using the Cell Cut Plus Laser micromanipulation system. The chromosomal DNA was digested by Sau 3A and ligated to Sau 3A linker adaptors. After two rounds of linker adaptor PCR (LA-PCR) amplification, DNA fragments ranging from 300 to 2,500 bp were acquired. Southern hybridization revealed that the PCR products had homology with genomic DNA of the cultivar Shixiya-1, indicating that DNA of chromosome 5 has been successfully amplified. The second round LA-PCR products and 45S rDNA and chromosome-specific BAC clones were used as probes for fluorescence in situ hybridization analysis on metaphase chromosome. The results confirmed that the LA-PCR products were derived from the isolated target chromosome. Hybridization signals of the second round LA-PCR products were mainly detected along the entire chromosome 5; in addition, weak signals were also observed on other chromosomes, indicating that there were some homologous nucleotide sequences in other chromosomes. The second round LA-PCR products were cloned to generate a chromosome-specific DNA library which contains approximately 173,000 clones. Evaluation based on 136 randomly selected clones showed that the size of the inserts varied from 500 to 1,800 bp with an average of 750 bp. The no-load rate was less than 1 %, the titer of the library was 1.2 × 10 pfu mL, and the rate of the single and low copy sequences was over 47 %. This library will facilitate specific probe screening, molecular mapping, gene cloning, and DNA sequencing for this chromosome. [ABSTRACT FROM AUTHOR]

A transgenic male sterile line of upland cotton was generated by the ectopic expression of the monooxygenase ( MNX) gene from Arabidopsis thaliana via Agrobacterium-mediated transformation. The bacterium harbored a plasmid pBinplus carrying a 1.25-kb MNX coding sequence together with a GUS reporter gene; the former was driven by the MS2 promoter of a male sterility gene in Arabidopsis, and the latter was under the control of CaMV 35S promoter. Twenty-seven putative transgenic plants (T0) were obtained, all of which showed GUS activity and positive signals of NPTII and MNX genes by PCR analysis, and also showed male sterility to some extent. It was further confirmed by Southern blotting that one copy of the NPTII and MNX gene was integrated in the genome of the plants which expressed male sterility to a higher degree. Northern blotting assay also demonstrated that the transgenes stably transcribed in the genome of the transgenic plants in F4 generation. The male sterile plants usually display lower plant height, shortened internodes, shrunken anthers without pollen grains or with some abortive pollen grains, and unusual leaves with deeper multi-lobes. Microscope observations on the meiosis processes of pollen mother cells (PMCs) showed that the abortion of pollen grains mainly resulted from abnormalities of meiosis such as direct degeneration of PMCs, degenerations of dyad and tetrads, amitosis, lagging chromosomes, and the multi-polar segregations of chromosomes and so on. This study indicates a method of developing novel cotton male sterile materials for potential application in agriculture and for engineering of male sterility in other important crops. [ABSTRACT FROM AUTHOR]