Isolation and Characterization of Defense Response Genes Involved in Neck Blast Resistance of Rice

Pi64, Encoding a Novel CC-NBS-LRR Protein, Confers Resistance to Leaf and Neck Blast in Rice

Rice blast caused by Magnaporthe oryzae poses a major threat to rice production worldwide. The utilization of host resistance (R) genes is considered to be the most effective and economic means to control rice blast. Here, we show that the japonica landrace Yangmaogu (YMG) displays a broader spectrum of resistance to blast isolates than other previously reported broad-spectrum resistant (BSR) cultivars. Genetic analysis suggested that YMG contains at least three major R genes. One gene, Pi64, which exhibits resistance to indica-sourced isolate CH43 and several other isolates, was mapped to a 43-kb interval on chromosome 1 of YMG. Two open reading frames (NBS-1 and NBS-2) encoding nucleotide-binding site and leucine-rich repeat proteins were short-listed as candidate genes for Pi64. Constructs containing each candidate gene were transformed into three susceptible japonica cultivars. Only transformants with NBS-2 conferred resistance to leaf and neck blast, validating the idea that NBS-2 represents the functional Pi64 gene. Pi64 is constitutively expressed at all development stages and in all tissues examined. Pi64 protein is localized in both the cytoplasm and nucleus. Furthermore, introgression of Pi64 into susceptible cultivars via gene transformation and marker-assisted selection conferred high-level and broad-spectrum leaf and neck blast resistance to indica-sourced isolates, demonstrating its potential utility in breeding BSR rice cultivars.

Physiological and proteome studies of responses to heat stress during grain filling in contrasting wheat cultivars

Experiments to explore physiological and biochemical differences of the effects of heat stress in ten wheat (Triticum aestivum L.) cultivars have been performed. Based on the response of photosynthesis rates, cell membrane lipid peroxide concentrations and grain yield to heat, six cultivars were clustered as heat-tolerant (cv. '579', cv. '810', cv. '1110', cv. Terice, cv. Taifun and cv. Vinjett) and four as heat-sensitive (cv. '490', cv. '633', cv. '1039' and cv. '1159'). Higher rates of photosynthetic carbon- and light-use were accompanied by lower damage to cell membranes in leaves of tolerant compared to sensitive cultivars under heat stress. The tolerant cv. '810' and the sensitive cv. '1039' were selected for further proteome analysis of leaves. Proteins related to photosynthesis, glycolysis, stress defence, heat shock and ATP production were differently expressed in leaves of the tolerant and sensitive cultivar under heat stress in relation to the corresponding control. The abundance of proteins related to signal transduction, heat shock, photosynthesis, and antioxidants increased, while the abundance of proteins related to nitrogen metabolism decreased in the tolerant cv. '810' under heat stress as compared to the control. Collectively, the results indicate that primarily changes in both the amount and activities of enzymes involved in photosynthesis and antioxidant activities in leaves contributed to higher heat tolerance in the cv. '810' compared to the heat sensitive cv. '1039'.

Expression patterns of defense genes in resistance of the panicles exserted from the caulis and from the tillers to neck blast in rice

The rice variety Xiushui227 is resistant to neck blast in the panicles exserted from the caulis but susceptible in the panicles from the tillers, however, the other variety Xiushui09 is susceptible to neck blast in the panicles from the caulis but resistant in the panicles from the tillers. These two varieties were used to analyze the expression patterns of defense genes in the panicles from the caulis and the first first-class tiller at the preliminary heading stage, after inoculating the necks in vitro with Magnaporthe oryzae, respectively. All defense genes (pathogenesis-related genes PR1a, Gns1 (1,3; 1,4-β-glucanase), Cht-1 (chitinase), PR4, PR5, and PR10a, secondary metabolite pathway genes PAL (phenylalanine ammonia-lyase), CHS (chalcone synthase), and LOX (lipoxygenase), and oxidative stress-related protein genes POX22.3 (peroxidase), and PPO (polyphenol oxidase)) used in this experiment except Cht-1 and PR5 could participate in defending Xiushui227 against neck blast in the panicles from the caulis. All defense genes used in this study except Cht-1, PR10a, and PPO may play roles in defending Xiushui09 against neck blast in the panicles from the tillers.

Expression of defense genes and antioxidant defense responses in rice resistance to neck blast at the preliminary heading stage and full heading stage

The rice variety Xiushui227 is resistant to neck blast at three crucial panicle stages (the booting stage, the preliminary heading stage (PHS), and the full heading stage (FHS)) that controlling neck blast. The other rice variety Liangyou6326 is susceptible to neck blast at these three panicle stages. These two varieties were used to analyze the expression patterns of defense genes and antioxidant defense responses at the PHS and FHS, after inoculating the necks in vitro with Magnaporthe oryzae, respectively. All defense genes (pathogenesis-related genes PR1a, Gns1 (1,3; 1,4-β-glucanase), Cht-1 (chitinase), PR4, PR5, and PR10a, secondary metabolite pathway genes PAL (phenylalanine ammonia-lyase), CHS (chalcone synthase), and LOX (lipoxygenase), and oxidative stress-related protein genes POX22.3 (peroxidase), and PPO (polyphenol oxidase)) used in this experiment except Cht-1, CHS and PPO could mainly play important roles in the resistance to neck blast at the PHS in Xiushui227, and CHS and PPO may primarily participate in fighting back against to neck blast at the FHS. Conversely, PR1a, Cht-1, PR4, PR10a, CHS, LOX-RLL, and PPO could chiefly play participate in defending Liangyou6326 against neck blast at the FHS, and PR5, PAL, and POX22.3 may be primarily involved in fighting back against to neck blast at the PHS. Furthermore, the antioxidant enzymes superoxide dismutase, peroxidase, and catalase may mainly participate in defending Xiushui227 against neck blast at the PHS and defending Liangyou6326 against neck blast at the FHS, respectively. Therefore oxidative damage is less at the PHS in Xiushui227 and at the FHS in Liangyou6326, respectively.

Expression patterns in soybean resistant to Phakopsora pachyrhizi reveal the importance of peroxidases and lipoxygenases

Soybean rust caused by Phakopsora pachyrhizi Sydow is a devastating foliar disease that has spread to most soybean growing regions throughout the world, including the USA. Four independent rust resistance genes, Rpp1-Rpp4, have been identified in soybean that recognize specific isolates of P. pachyrhizi. A suppressive subtraction hybridization (SSH) complementary DNA (cDNA) library was constructed from the soybean accession PI200492, which contains Rpp1, after inoculation with two different isolates of P. pachyrhizi that result in susceptible or immune reactions. Both forward and reverse SSH were performed using cDNA from messenger RNA pooled from 1, 6, 12, 24, and 48 h post-inoculation. A total of 1,728 SSH clones were sequenced and compared to sequences in GenBank for similarity. Microarray analyses were conducted on a custom 7883 soybean-cDNA clone array encompassing all of the soybean-rust SSH clones and expressed sequence tags from four other soybean cDNA libraries. Results of the microarray revealed 558 cDNA clones differentially expressed in the immune reaction. The majority of the upregulated cDNA clones fell into the functional category of defense. In particular, cDNA clones with similarity to peroxidases and lipoxygenases were prevalent. Downregulated cDNA clones included those with similarity to cell-wall-associated protein, such as extensins, proline-rich proteins, and xyloglucan endotransglycosylases.