稻瘟菌无毒基因研究进展

无毒基因编码的产物激发病原物与植物特异性相互作用。水稻与稻瘟菌之间的特异互作符合“基因对基因”关系。从研究稻瘟菌无毒基因的意义、已鉴定和克隆的稻瘟菌无毒基因、稻瘟菌无毒基因与其抗病基因的互作特点等几个方面,对稻瘟菌无毒基因研究进展作了简要评述 。     

Modulation of Nociceptive Responses by Electrical Stimulation of the Nucleus Raphe Dorsalis and Midbrain Substantia Grisea Centralis in Cat

In chronic experiments on 20 awake cats, we studied modulation of nociceptive responses to intense noxious stimulation of the skin of the hindlimb (electrical cutaneous stimulation, ECS) after electrical stimulation of some parts of the brainstem had been applied through chronically implanted electrodes. The stimulated structures were as follows: the nucleus raphe dorsalis, RD, and the dorsolateral zone of the rostral section or the ventrolateral zone of the middle section of the midbrain central gray matter (substantia grisea centralis, SGC), dl SGC and vl SGC, respectively. Freely moving animals were subjected to ECS applied either in isolation or against the background of stimulation of one of the above-mentioned brainstem structures. Integral intensity of nociceptive responses was scored on a four-point scale. In this case, the characteristics of the motor (drawing back of the leg and generalized motor reactions, i.e., change in the posture, episodes of pace, etc.), autonomic (changes in the heart rate, respiratory rate, and respiration depth), and emotional (vocalization, reactions of anxiety and aggression) components of the nociceptive response were taken into account. The strength of standard isolated ECS was selected such that it caused a nociceptive response of the level 3. The same ECS strength, but applied against the background of preliminary stimulation of the vl SGC, in 85% of the tests caused the development of a significantly more intense response (level 4). Under the influence of ECS against the background of stimulation of the dl SGC or RD, in the overwhelming majority of cases, only level-1 responses developed. To obtain a nociceptive level-3 response against the background of stimulation of the dl SGC and RD, the ECS strength should be increased at least twice. Isolated vl SGC stimulation caused nociceptive responses, which as a whole corresponded to level 2. Control isolated stimulation of the dl SGC and RD either did not result in any noticeable behavioral change or evoked minimum responses. We conclude that the SGC with respect to the nociceptive/antinociceptive systems is heterogeneous; the vl SGC should be considered the nociceptive zone, while the dl SGC and RD should be considered the antinociceptive brainstem zones.     

Mapping of four major rice blast resistance genes from ’Lemont’ and ’Teqing’ and evaluation of their combinatorial effect for field resistance

A framework linkage map was developed using 284 F₁₀ recombinant inbred lines (RILs) from a ’Lemont’×’Teqing’ rice cultivar cross. Evaluation of a subset of 245 of these RILs with five races of the rice blast pathogen permitted RFLP mapping of three major resistance genes from Teqing and one major gene from Lemont. All mapped genes were found to confer resistance to at least two blast races, but none conferred resistance to all five races evaluated. RFLP mapping showed that the three resistance genes from Teqing, designated Pi-tq5, Pi-tq1 and Pi-tq6, were present on chromosomes 2, 6 and 12, respectively. The resistance gene from Lemont, Pi-lm2, was located on chromosome 11. Pi-tq1 is considered a new gene, based on its reaction to these five races and its unique map location, while the other three genes may be allelic with previously reported genes. Lines with different gene combinations were evaluated for disease reaction in field plots. Some gene combinations showed both direct effects and non-linear interaction. The fact that some of the lines without any of the four tagged genes exhibited useful levels of resistance in the field plots suggests the presence of additional genes or QTLs affecting the blast reaction segregating in this population. Received: 16 December 1999 / Accepted: 28 February 2000     

稻瘟病分子生物学研究进展

稻瘟病分子生物学发展迅速,已分子标记定位的稻瘟病主效抗性基因１５个,微效抗性基因３个;水稻抗稻瘟病基因Ｐｉ－ｔａ和Ｐｉ－ｂ已成功克隆。稻瘟病菌系谱与致病型关系可分为简单与复杂两种类型。本文对水稻抗稻瘟病基因的定位和克隆,稻瘟病菌群体遗传结构,致病性遗传、基因组分析、无毒基因克隆、准性生殖等研究进展进行了评述。     

稻瘟菌糖蛋白激发子诱导的水稻叶片膜脂过氧化及过敏性反应

将稻瘟菌细胞壁来源的专化性糖蛋白激发子接种于一套水稻抗稻瘟病近等基因系后,非亲和性互作水稻超氧阴离子(O-.2)积累在互作早期明显高于亲和性互作水稻;超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性均趋于下降,不同亲和性互作水稻间的差异不明显;脂氧合酶(LOX)活性在水稻/激发子非亲和互作早期增加明显、速度快;这些指标的变化进而导致非亲和性互作水稻的膜脂过氧化,其相对电导率及丙二醛(MDA)含量的高峰期和强度也明显早于和高于亲和性互作水稻.非亲和性互作水稻过氧化物酶(POD)活性在互作早期明显高于亲和性互作水稻,可能与其参与其它抗性有关.研究同时表明,激发子可专化性诱导完全和高度非亲和性互作水稻的过敏性坏死反应;而中度非亲和性互作和亲和性互作水稻则未发生过敏性(HR)坏死反应.这些结果表明,膜脂过氧化和HR反应的发生是激发子诱导水稻抗性的主要生理机制之一.     

Purification and anti-fungal activity of chitinase against Pyricularia grisea in finger millet

Pseudomonas fluorescens isolate 1 (Pfl) protected finger millet plants treated with the ragi blast fungus, Pyricularia grisea, by upto 27% depending on the cultivar. Induction of pathogenesis-related proteins, viz., chitinase by Pfl isolate, was studied against Py. grisea. The activity of chitinase from plants treated with Pfl was significantly higher than the control plant after pathogen inoculation in all cultivars tested. Chitinase in the cultivars, with and without challenge by Py. grisea, revealed changes in the isoform pattern by western blot analysis. Chitinase was purified by affinity chromatography from the Pfl-treated leaves. It showed a single band at 57 kDa after SDS-PAGE. Western blot analysis using barley chitinase antiserum confirmed a 57 kDa chitinase. The chitinase had anti-fungal activity against Py. grisea in vitro. This revised version was published online in August 2006 with corrections to the Cover Date.     

Increased tryptophan decarboxylase and monoamine oxidase activities induce Sekiguchi lesion formation in rice infected with Magnaporthe grisea

Sekiguchi lesion (sl)-mutant rice infected with Magnaporthe grisea showed increased light-dependent tryptophan decarboxylase (TDC) and monoamine oxidase (MAO) activities. TDC and MAO activities were observed before the penetration of M. grisea to rice cells and maintained high levels even after Sekiguchi lesion formation. Light-dependent expression of TDC gene was observed in leaves inoculated with M. grisea before Sekiguchi lesion formation. Spore germination fluid (SGF) of M. grisea also induced Sekiguchi lesion formation accompanied by increased enzymes activities and tryptamine accumulation. Sekiguchi lesion was also induced by treatments with tryptamine and beta-phenylethylamine, which are substrates for MAO, but was not induced by non-substrates such as indole-3-propionic acid, (+/-)-phenylethylamine and tryptophan under light. Light-dependent induction of Sekiguchi lesion by tryptamine was significantly inhibited in the presence of MAO inhibitors, metalaxyl and semicarbazide, and H2O2-scavengers, ascorbic acid and catalase. H2O2 in M. grisea-infected leaves with and without Sekiguchi lesions was demonstrated directly in situ by strong 3,3'-diaminobenzidine (DAB) staining. On the other hand, H2O2 induced Sekiguchi lesions on leaves of cv. Sekiguchi-asahi under light, but not in darkness. This difference was associated with the decrease of catalase activity in infected leaves under light and the absence of decrease in darkness. We hypothesize that the H2O2-induced breakdown of cellular organelles such as chloroplasts and mitochondria in mesophyll cells may cause high TDC and MAO activities and the development of Sekiguchi lesion, and that the sl gene products in wild-type rice may function as a suppressor of organelle breakdown caused by chemical or environmental stress.     

Overexpression of Bax inhibitor suppresses the fungal elicitor-induced cell death in rice (Oryza sativa L) cells

Treatment of suspension-cultured cells of rice (Oryza sativa L.) with cell wall extract of rice blast fungus (Magnaporthe grisea) elicits a rapid generation of H2O2, alkalinization of culture medium, and eventual cell death. To elucidate genes involved in these processes, we exploited SAGE (Serial Analysis of Gene Expression) technique for the molecular analysis of cell death in suspension-cultured cells treated with the elicitor. Among the downregulated genes in the elicitor-treated cells, a BI-1 gene coding for Bax inhibitor was identified. Transgenic rice cells overexpressing Arabidopsis BI-1 gene showed sustainable cell survival when challenged with M. grisea elicitor. Thus, the plant Bax inhibitor plays a functional role in regulating cell death in the rice cell culture system.     

A New Antibiotic K-52B

A new antibiotic K-52B, different from K-52A, was isolated from the culture broth of Streptoverticillium roseoverticillatum subsp. albosporum, strain No. K-52. The antibiotic K-52B was thought to be a similar saccharide to K-52A from its physicochemical properties but differed from K-52A in the presence of nitrogen content. Antibiotic K-52B inhibited the growth of Gram-positive and Gram-negative bacteria, including Pseudomonas aeruginosa on a chemically defined medium. The growth inhibition was, however, reversed by l-glutamine, l-glutamic acid, l-asparagine and l-aspartic acid.