Xianbi Li

spatiotemporal manipulation of auxin biosynthesis in cotton ovule epidermal cells enhances fiber yield and quality

The capacity of conventional breeding to simultaneously improve the yield and quality of cotton fiber is limited. The accumulation of the plant hormone indole-3-acetic acid (IAA) in cotton fiber initials prompted us to investigate the effects of genetically engineering increased IAA levels in the ovule epidermis. Targeted expression of the IAA biosynthetic gene iaaM, driven by the promoter of the petunia MADS box gene Floral Binding protein 7 (FBP7), increased IAA levels in the epidermis of cotton ovules at the fiber initiation stage. This substantially increased the number of lint fibers, an effect that was confirmed in a 4-year field trial. The lint percentage of the transgenic cotton, an important component of fiber yield, was consistently higher in our transgenic plants than in nontransgenic controls, resulting in a >15% increase in lint yield. Fiber fineness was also notably improved.

Gibberellin 20-oxidase promotes initiation and elongation of cotton fibers by regulating gibberellin synthesis

Cotton is the leading natural fiber, and gibberellin (GA) is a phytohormone involved in the development of cotton fibers. However, it is largely unknown how the GA content in ovules and fibers is regulated and how the endogenous GA concentration affects fiber development. To address these questions, three GA 20-oxidase homologous genes (GhGA20ox1-3) were cloned and the endogenous bioactive GA content in developing ovules and fibers determined by liquid chromatography-electrospray ionization-mass spectrometry. Real-time reverse transcription PCR (RT-PCR) revealed that GhGA20ox1 expressed preferentially in elongating fibers and that the expression level varied with the endogenous GA content consistently, while GhGA20ox2 and GhGA20ox3 transcripts accumulated mainly in ovules. The GA accumulation kinetics as well as the GhGA20ox expression differed in ovules and the attached fibers, suggesting relatively independent GA regulation system in these two sites. Transgenic cotton, over-expressing GhGA20ox1, showed GA over-production phenotypes with increased endogenous GA levels (especially GA(4)) in fibers and ovules. It also produced significantly more fiber initials per ovule, and fiber lengths was increased compared with the control, which demonstrates that up-regulation of the GhGA20ox1 gene promoted fiber initiation and elongation. Our results suggest that GA 20-oxidase is involved in fiber development by regulating GA levels, and corresponding genes might be employed as target genes for the manipulation of fiber initiation and elongation in cotton.

Isolation and characterization of a novel thermostable non-specific lipid transfer protein-like antimicrobial protein from motherwort (Leonurus japonicus Houtt) seeds

In screening for potent antimicrobial proteins from plant seeds, a novel heat-stable antimicrobial protein, designated LJAMP2, was purified from seeds of the motherwort (Leonurus japonicus Houtt), a medicine herb, with a procedure involving cation exchange chromatography on a CM FF column, and reverse phase HPLCs on C8 column and C18 column. LJAMP2 exhibited a molecular mass of 6.2 kDa determined. Automated Edman degradation determined the partial N-terminal sequence of LJAMP2 to be NH2-AIGCNTVASKMAPCLPYVTGKGPLGGCCGGVKGLIDAARTTPDRQAVCNCLKTLAKSYSG, which displays homology with plant non-specific lipid transfer proteins (nsLTPs). In vitro bioassays showed that LJAMP2 inhibits the growth of a variety of microbes, including filamentous fungi, bacteria and yeast. The growth of three phytopathogenic fungi, Alternaria brassicae, Botrytis maydis, and Rhizoctonia cerealis, are inhibited at 7.5 microM of LJAMP2, whereas Bacillus subtilis is about 15 microM. The IC(50) of LJAMP2 for Aspergillus niger, B. maydis, Fusarium oxysporum, Penicillium digitatum and Saccharomyces cerevisiae are 5.5, 6.1, 9.3, 40.0, and 76.0 microM, respectively.

Characterization and expression of an nsLTPs-like antimicrobial protein gene from motherwort (Leonurus japonicus).

In screening for potent antimicrobial proteins (AMPs) from plant seeds, we had purified a heat-stable AMP, LJAMP2, from the seeds of a medicine herb, motherwort (Leonurus japonicus Houtt). In an in vitro assay, the protein can inhibit the growth of both fungi and bacteria. Then a cDNA encoding LJAMP2 was cloned by the rapid amplification of cDNA ends based on the N-terminal amino acid sequence determined. The deduced amino acid sequences of this cDNA show similarity to plant non-specific lipid transfer proteins. Northern blotting assay revealed that this nsLTP-like gene, designated LJAMP2, was expressed in seeds. Overexpression of LJAMP2 in tobacco enhanced resistance to the fungal pathogen Alternaria alternata and the bacterial pathogen Ralstoniasolanacearum, significantly, while no visible alteration in plant growth and development. Our data confirm the antifungal and antibacterial function of LJAMP2 from motherwort seeds and suggest the potential of LJAMP2 in improving disease resistance in plants.

The phosphatidylinositol synthase gene (GhPIS) contributes to longer, stronger, and finer fibers in cotton

Cotton fibers are the most important natural raw material used in textile industries world-wide. Fiber length, strength, and fineness are the three major traits which determine the quality and economic value of cotton. It is known that exogenous application of phosphatidylinositols (PtdIns), important structural phospholipids, can promote cotton fiber elongation. Here, we sought to increase the in planta production of PtdIns to improve fiber traits. Transgenic cotton plants were generated in which the expression of a cotton phosphatidylinositol synthase gene (i.e., GhPIS) was controlled by the fiber-specific SCFP promoter element, resulting in the specific up-regulation of GhPIS during cotton fiber development. We demonstrate that PtdIns content was significantly enhanced in transgenic cotton fibers and the elevated level of PtdIns stimulated the expression of genes involved in PtdIns phosphorylation as well as promoting lignin/lignin-like phenolic biosynthesis. Fiber length, strength and fineness were also improved in the transgenic plants as compared to the wild-type cotton, with no loss in overall fiber yield. Our data indicate that fiber-specific up-regulation of PtdIns synthesis is a promising strategy for cotton fiber quality improvement.