Cotton PRP5 gene encoding a proline-rich protein is involved in fiber development

Proline-rich proteins contribute to cell wall structure of specific cell types and are involved in plant growth and development. In this study, a fiber-specific gene, GhPRP5, encoding a proline-rich protein was functionally characterized in cotton. GhPRP5 promoter directed GUS expression only in trichomes of both transgenic Arabidopsis and tobacco plants. The transgenic Arabidopsis plants with overexpressing GhPRP5 displayed reduced cell growth, resulting in smaller cell size and consequently plant dwarfs, in comparison with wild type plants. In contrast, knock-down of GhPRP5 expression by RNA interference in cotton enhanced fiber development. The fiber length of transgenic cotton plants was longer than that of wild type. In addition, some genes involved in fiber elongation and wall biosynthesis of cotton were up-regulated or down-regulated in the transgenic cotton plants owing to suppression of GhPRP5. Collectively, these data suggested that GhPRP5 protein as a negative regulator participates in modulating fiber development of cotton.     

The CaPRP1 gene encoding a putative proline-rich glycoprotein is highly expressed in rapidly elongating early roots and leaves in hot pepper (Capsicum annuum L. cv. Pukang)

Most of the proline-rich cell wall glycoprotein genes isolated from higher plants are preferentially expressed in the transmitting tissues of the flower organ. In conducting expressed sequence tag (EST) analysis, which was prepared from 5-day-old early roots of hot pepper (Capsicum annuum L. cv. Pukang), we identified a cDNA clone, pCaPRP1, encoding a putative cell wall proline-rich glycoprotein. CaPRP1 (Mr=28 kDa, pI=9.98) was most closely related to Nicotiana alata NaPRP4 (71%), while most distantly related to soybean PvPRP (37%). The predicted primary structure of CaPRP1 contains a putative N-terminal signal peptide, six repeats of the Lys-Pro-Pro tripeptide, four repeats of a five-amino acid sequence [Pro-(Ser/The)-Pro-Pro-Pro] and one potential N-glycosylation site (Asn-Asn-Ser). In contrast to most proline-rich cell wall glycoprotein genes, CaPRP1 was highly expressed in rapidly elongating very early roots and young leaves as well as developing flower tissues. Although the physiological function of CaPRP1 is not yet clear, there are several possibilities for its role in cell expansion and elongation during early development of hot pepper plants.     

Molecular characterization of a gene encoding a cysteine-rich protein preferentially expressed in anthers of Lycopersicon esculentum

The tomato (Lycopersicon esculentum Mill.) cDNA clone TomA5B was isolated by differential screening of a cDNA library prepared from anthers at late meiosis to tetrad formation. The 5B gene is present in a single copy in the tomato genome. Expression is developmentally regulated and tissue specific. RNA accumulation was detected from premeiosis through tetrad release in the tapetal cell layer of the anther with low levels of RNA detected in petals and early stages of pistil development. The protein deduced from the DNA sequence analysis is predicted to have a molecular mass of 11.1 kDa and a secretory signal sequence, suggesting it is a secreted protein. The deduced 5B protein has a pattern of cysteine residues that is similar to other proteins that have stamen-specific expression and to a superfamily of seed proteins. The 5B protein is unique in that there is no amino acid sequence similarity to other proteins beyond the similar cysteine motif.     

Purification of a plant cell wall fibronectin-like adhesion protein involved in plant response to salt stress

The structural role of extracellular-matrix (ECM) has been recognized in both plants and animals as a support and anchorage-inducing cell behavior. Unlike the animal ECM proteins, the proteins that have been identified in plant ECM have not yet been purified from whole plants and cell wall. As several immunological data indicate the presence of animal ECM-like proteins in plants cell wall, especially under salt stress or water deficit, we propose a protocol to purify a fibronectin-like protein from the cell wall of epicotyls of young germinating peas. The process consists of a combination of gelatin and heparin affinity chromatography, close to the classical one used for human blood plasma fibronectin purification. Proteins with affinity for gelatin and heparin, immunologically related to human fibronectin, are found in the cell wall of epicotyls grown under salt stress or not. Total amount of purified proteins is 3-4 times more enriched in salt stressed epicotyls. SDS-PAGE and Western blot with antibodies directed against human blood plasma fibronectin give evidence that the cell wall proteins purified by gelatin/heparin affinity chromatography are closely related to human fibronectin. The present protocol leads us to purify 17 (control) or 65 (salt stress) micrograms of protein per g of fresh starting material. Our results suggest that plant cell wall proteins can provide better anchorage of the cell to its cell-wall during salt stress or water deficit and could be considered not only as cell adhesion but also as signaling molecules.     

IMPa-4, an Arabidopsis importin alpha isoform, is preferentially involved in agrobacterium-mediated plant transformation

Successful transformation of plants by Agrobacterium tumefaciens requires that the bacterial T-complex actively escorts T-DNA into the host's nucleus. VirD2 and VirE2 are virulence proteins on the T-complex that have plant-functional nuclear localization signal sequences that may recruit importin alpha proteins of the plant for nuclear import. In this study, we evaluated the involvement of seven of the nine members of the Arabidopsis thaliana importin alpha family in Agrobacterium transformation. Yeast two-hybrid, plant bimolecular fluorescence complementation, and in vitro protein-protein interaction assays demonstrated that all tested Arabidopsis importin alpha members can interact with VirD2 and VirE2. However, only disruption of the importin IMPa-4 inhibited transformation and produced the rat (resistant to Agrobacterium transformation) phenotype. Overexpression of six importin alpha members, including IMPa-4, rescued the rat phenotype in the impa-4 mutant background. Roots of wild-type and impa-4 Arabidopsis plants expressing yellow fluorescent protein-VirD2 displayed nuclear localization of the fusion protein, indicating that nuclear import of VirD2 is not affected in the impa-4 mutant. Somewhat surprisingly, VirE2-yellow fluorescent protein mainly localized to the cytoplasm of both wild-type and impa-4 Arabidopsis cells and to the cytoplasm of wild-type tobacco (Nicotiana tabacum) cells. However, bimolecular fluorescence complementation assays indicated that VirE2 could localize to the nucleus when IMPa-4, but not when IMPa-1, was overexpressed.     

Genes encoding small GTP-binding proteins analogous to mammalian rac are preferentially expressed in developing cotton fibers

In animals, the small GTP-binding proteins, Rac and Rho, of theras superfamily participate in the signal rransduction pathway that regulates the organization of the actin cytoskeleton. We report here on the characterization of two distinct cDNA clones isolated from a cotton fiber cDNA library that code for homologs of animal Rac proteins. Using gene-specific probes, we have determined that amphidiploid cotton contains two genes that code for each of the two Rac proteins, designated Rac13 and Rac9, respectively. The gene for Rac13 shows highly enhanced expression in developing cotton fibers, with maximal expression occurring at the time of transition between primary and secondary wall synthesis. This is also the time at which reorganization of the cytoskeleton occurs, and thus the pattern of expression of Rac13 is consistent with its possible role, analogous to animal Rac, in the signal transduction pathway that controls cytoskeletal organization.