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We carried out activation tagging screen to isolate genes regulating abscisic acid (ABA) response. From the screen of approximately 10,000 plants, we isolated ca 100 ABA response mutants. We characterized one of the mutants, designated ahs1, in this study. The mutant is ABA-hypersensitive, and AtMYB52 was found to be activated in the mutant. Overexpression analysis to recapitulate the mutant phenotypes demonstrated that ATMYB confers ABA-hypersensitivity during postgermination growth. Additionally, AtMYB52 overexpression lines were drought-tolerant and their seedlings were salt-sensitive. Changes in the expression levels of a few genes involved in ABA response or cell wall biosynthesis were also observed. Together, our data suggest that AtMYB52 is involved in ABA response. Others previously demonstrated that AtMYB52 regulates cell wall biosynthesis; thus, our results imply a possible connection between ABA response and cell wall biosynthesis.

Expansins are non-hydrolytic cell wall-loosening proteins that are involved in the cell wall modifications that underlie many plant developmental processes. Root hair growth requires the accumulation of cell wall materials and dynamic cell wall modification at the tip region. Although several lines of indirect evidence support the idea that expansin-mediated wall modification occurs during root hair growth, the involvement of these proteins remains to be demonstrated in vivo. In this study, we used RNA interference (RNAi) to examine the biological function of Arabidopsis thaliana EXPANSIN A7 (AtEXPA7), which is expressed specifically in the root hair cell. The root hairspecific AtEXPA7 promoter was used to drive RNAi expression, which targeted two independent regions in the AtEXPA7 transcript. Quantitative reverse transcriptase-PCR analyses were used to examine AtEXPA7 transcript levels. In four independent RNAi transformant lines, RNAi expression reduced AtEXPA7 transcript levels by 25-58% compared to controls. Accordingly, the root hairs of RNAi transformant lines were 25-48% shorter than control plants and exhibited a broader range of lengths than the controls. Our results provide in vivo evidence that expansins are required for root hair tip growth.

Expansins are extracellular proteins that increase plant cell wall extensibility in vitro. Beads loaded with purified expansin induced bulging on the leaf-generating organ, the apical meristem, of tomato plants. Some of these bulges underwent morphogenesis to alpha-produce leaflike structures, resulting in a reversal of the direction of phyllotaxis. Thus, expansin can induce tissue expansion in vivo, and localized control of tissue expansion may be sufficient to induce leaf formation. These results suggest a role for biophysical forces in the regulation of plant development

Protoplasts are microbial or vegetable cells lacking a cell wall. These can be obtained from microalgae by an enzymatic hydrolysis process in the presence of an osmotic stabilizer. In general, protoplasts are experimentally useful in physiological, geneticand bio-chemical studies, so their acquisition and fusion will continue to be an active research area in modern biotechnology. The fusion of protoplasts in microalgae constitutes a tool for strain improvement because it allows both intra and interspecific genetic recombina-tion, resulting in organisms with new or improved characteristics of industrial interest. In this review we briefly describe themethod-ology for obtaining protoplasts, as well as fusion methods and the main applications of microalgal platforms.

Summary Background: contamination of barley with Fusarium mycotoxins causes significant economic losses for pork producers, and alleviation with mycotoxin sequestering agents has proven inconsistent. Objective: to evaluate a yeast cell wall product in preventing adverse effects of Fusarium mycotoxins on growth performance, blood characteristic, and nutrient digestibility in gilts fed diets containing barley naturally contaminated with Fusarium mycotoxins. Methods: positive and negative controls of corn-soybean meal diets containing 20% control and contaminated barley with Fusarium mycotoxins, respectively, were prepared. Two additional diets were prepared by adding 0.2 or 0.4% of a yeast cell wall product to the negative control diet. The experimental diets were fed to pigs with 61.7 Kg initial body weight for 2 weeks. Results: pigs fed the negative control diet gained less than those fed the positive control diet (p<0.05) from d 0 to 7 and during the overall period, but nutrient digestibility and blood characteristics were not affected by feeding the contaminated diet. Most measurements were not affected by supplementing the yeast cell wall to the negative control diet. Conclusion: addition of the yeast cell wall product to negative control diets failed to ameliorate the adverse effects of dietary Fusarium mycotoxin on growth performance. Resumo Antecedentes: a contaminação da cevada com a micotoxinas Fusarium causa perdas econômicas significativas para os produtores de suínos, porèm os adsorventes de micotoxinas que evitam efeitos prejudiciais de micotoxinas não deram resultados consistentes. Objetivo: avaliar o produto da parede celular das leveduras para prevenir efeitos adversos da micotoxinas Fusarium no desempenho do crescimento, inchaço da vulva, característica do sangue, digestibilidade dos nutrientes em porcas jòvens que são alimentadas com dietas contendo a cevada naturalmente contaminada com micotoxinas do Fusarium. Métodos: foram preparadas dietas de controle positivo e negativo à base de milho e soja, contendo 20% do controle e cevada contaminada com micotoxinas Fusarium, respectivamente. Duas dietas adicionais foram preparadas complementando com 0,2 ou 0,4% o produto da parede celular das leveduras à dieta do controle negativo. As dietas experimentais foram fornecidas aos suínos com peso corporal inicial de 61,7 Kg por 2 semanas. Resultados: os suínos alimentados com a dieta do controle negativo ganharam menos peso do que aqueles alimentados com a dieta do controle positivo (p<0,05) a partir do dia 0 até 7 durante todo o período, a digestibilidade dos nutrientes e as características do sangue não foram afetadas pela alimentação da dieta contaminada. A maioria das medidas não foram afetadas pela complementação da parede celular das leveduras à dieta do controle negativo. Conclusão: a complementação do produto da parede celular das leveduras nas dietas de controle negativo não conseguiu melhorar o efeito adverso das micotoxinas Fusariume no desempenho de crescimento. Resumen Antecedentes: la contaminación de la cebada con micotoxinas de Fusarium causa importantes pérdidas económicas para los productores de carne de cerdo, pero adsorbentes de micotoxinas para prevenir los efectos perjudiciales de las micotoxinas no dieron resultados consistentes. Objetivo: evaluar el producto de la pared celular de la levadura en la prevención de los efectos adversos de las micotoxinas de Fusarium sobre el crecimiento, características de la sangre, y la digestibilidad de nutrientes en cerdas jóvenes alimentadas con dietas que contienen cebada naturalmente contaminada con micotoxinas de Fusarium. Métodos: se prepararon las dietas a base de harina de maíz-soja de control positivo y negativo contienen 20% de control y cebada contaminados con micotoxinas de Fusarium, respectivamente. Adicionalmente se prepararon 2 dietas con productos de la pared celular de levadura de 0,2 o 0,4% a la dieta de control negativo. Fueron alimentados con las dietas experimentales cerdos con un peso corporal inicial de 61,7 Kg durante 2 semanas. Resultados: los cerdos alimentados con la dieta control negativo ganaron menos que aquellos alimentados con la dieta control positivo (p<0,05) a partir del d 0 a 7 y durante el período en general, pero la digestibilidad de los nutrientes y características de la sangre no fueron afectados por la alimentación de la dieta contaminada. La mayoría de las mediciones no fueron afectadas por la suplementación de la pared celular de la levadura con la dieta control negativo. Conclusión: la adición del producto de pared celular de levadura a la dieta control negativo no logró aminorar los efectos adversos de las micotoxinas de Fusarium sobre el crecimiento.

Cell differentiation ultimately relies on the regulation of cell type-specific genes. For a root hair cell to undergo morphogenesis, diverse cellular processes including cell-wall loosening must occur in a root hair cell-specific manner. Previously, we identified and characterized root hair-specific cis-elements (RHE) from the genes encoding the cell wall-loosening protein EXPANSIN A (EXPA) which functions preferentially on dicot cell walls. This study reports two root hair-specific grass EXPB genes that contain RHEs. These genes are thought to encode proteins that function more efficiently on grass cell walls. The proximal promoter regions of two orthologous EXPB genes from rice (Oryza sativa; OsEXPB5) and barley (Hordeum vulgare; HvEXPB1) included RHE motifs. These promoters could direct root hair-specific expression of green fluorescent protein (GFP) in the roots of rice and Arabidopsis (Arabidopsis thaliana). Promoter deletion analyses demonstrated that the RHE motifs are necessary for root hair-specific expression of these EXPB promoters. Phylogenetic analysis of EXP protein sequences indicated that grass EXPBs are the only orthologs to these root hair-specific EXPBs, separating dicot EXPBs to distal branches of the tree. These results suggest that RHE-containing root hair-specific EXPB genes have evolved for grass-specific cell wall modification during root hair morphogenesis.

The rice blast fungus, Magnaporthe grisea, generates enormous turgor pressure within a specialized cell called the appressorium to breach the surface of host plant cells. Here, we show that a mitogen-activated protein kinase, Mps1, is essential for appressorium penetration. Mps1 is 85% similar to yeast Slt2 mitogen-activated protein kinase and can rescue the thermosensitive growth of slt2 null mutants. The mps1-1 delta mutants of M. grisea have some phenotypes in common with slt2 mutants of yeast, including sensitivity to cell-wall-digesting enzymes, but display additional phenotypes, including reduced sporulation and fertility. Interestingly, mps1-1 delta mutants are completely nonpathogenic because of the inability of appressoria to penetrate plant cell surfaces, suggesting that penetration requires remodeling of the appressorium wall through an Mps1-dependent signaling pathway. Although mps1-1 delta mutants are unable to cause disease, they are able to trigger early plant-cell defense responses, including the accumulation of autofluorescent compounds and the rearrangement of the actin cytoskeleton. We conclude that MPS1 is essential for pathogen penetration; however, penetration is not required for induction of some plant defense responses

Wounding stress induces the accumulation of phenolics in carrots. However, its effect on cell-wall constituents has not been studied. Extrusion generates modifications in high-fiber food matrices. In this study, the combined effect of wounding stress and extrusion on cell-wall constituents and functional properties of carrots was evaluated. Wounding stress was applied by shredding carrots and storing the tissue (48 h/15°C). The stressed tissue (wounding stress carrot, WSC) was dehydrated and then extruded at temperature, 60 or 100°C, and screw configuration, continuous or expansion. Extrudates were milled and analyzed for cell-wall constituents and other physicochemical parameters. Cellulose content increased (112%) as a response to wounding. Furthermore, extrudates obtained from WSC showed higher content of cell-wall components. For instance, insoluble and total lignin content increased (54-84%) with extrusion conditions. Furthermore, WSC showed higher oil absorption index and lower water solubility index (WSI); whereas extrudates showed the highest WSI.

To develop antibody probes for the neutral side chains of pectins, antisera were generated to a pectic galactan isolated from tomato (Lycopersicon esculentum) pericarp cell walls and to a (1 leads to 4)-beta-galactotetraose-bovine serum albumin neoglycoprotein. The use of these two antisera in immunochemical assays and immunolocalization studies indicated that they had very similar specificities. A monoclonal antibody (LM5) was isolated and characterized subsequent to immunization with the neoglycoprotein. Hapten inhibition studies revealed that the antibody specifically recognized more than three contiguous units of (1 leads to 4)-beta-galactosyl residues. The antigalactan antibody was used to immunolocalize the galactan side chains of pectin in tomato fruit pericarp and tomato petiole cell walls. Although the LM5 epitope occurs in most cell walls of the tomato fruit, it was absent from both the locular gel and the epidermal and subepidermal cells. Furthermore, in contrast to other anti-pectin antibodies, LM5 did not label the cell wall thickenings of tomato petiole collenchyma

▪ Abstract  New and exciting developments in boron research in the past few years greatly contributed to better understanding of the role of boron in plants. Purification and identification of the first boron-polyol transport molecules resolved much of the controversy about boron phloem mobility. Isolation and characterization of the boron-polysaccharide complex from cell walls provided the first direct evidence for boron crosslinking of pectin polymers. Inhibition and recovery of proton release upon boron withdrawal and restitution in plant culture medium demonstrated boron involvement in membrane processes. Rapid boron-induced changes in membrane function could be attributed to boron-complexing membrane constituents. Boron may affect metabolic pathways by binding apoplastic proteins to cis-hydroxyl groups of cell walls and membranes, and by interfering with manganese-dependent enzymatic reactions. In addition, boron has been implicated in counteracting toxic effects of aluminum on root growth of dicotyledonous plants. Molecular investigations of boron nutrition have been initiated by the discovery of a novel mutant of Arabidopsis thaliana with an altered requirement for boron.