光照,湿度和培养基对苎麻疫霉卵孢子产生量的影响

采用３因素随机区组设计研究了光照、湿度和培养基对苎麻疫霉（Ｐｈｙｔｏｐｈｔｈｏｒａｂｏｅｈｍｅｒｉａｅ）卵孢子产生量的影响．结果表明,各因子对卵孢子产生量的影响效应大小次序为培养基＞光照＞湿度,其中培养基和光照两因子影响均在０．０１水平上显著．在供试的４种常用培养基上,卵孢子产生量的大小次序为：ＳＬＡ培养基（ＳＬＡ）＞利马豆培养基（ＬＢＡ）＞Ｖ６汁培养基（Ｖ６Ａ）＞澄清的Ｖ６汁培养基（Ｖ６Ｂ）．在设置的３种光照条件中,卵孢子产生量以连续黑暗处理最高,连续光照最低,光照与黑暗交替处理居中．３个试验因子间的所有互作对卵孢子产生量均有极显著的影响．在不同光照、湿度、培养基组合中,卵孢子产生量以低湿＋连续黑暗＋ＳＬＡ组合最高,低湿＋连续光照＋Ｖ６Ｂ组合最低．     

A single region of the Phytophthora infestans avirulence effector Avr3b functions in both cell death induction and plant immunity suppression

As a destructive plant pathogen, Phytophthora infestans secretes diverse host-entering RxLR effectors to facilitate infection. One critical RxLR effector, PiAvr3b, not only induces effector-triggered immunity (ETI), which is associated with the potato resistance protein StR3b, but also suppresses pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). To date, the molecular basis underlying such dual activities remains unknown. Based on phylogenetic analysis of global P. infestans isolates, we found two PiAvr3b isoforms that differ by three amino acids. Despite this sequence variation, the two isoforms retain the same properties in activating the StR3b-mediated hypersensitive response (HR) and inhibiting necrosis induced by three PAMPs (PiNpp, PiINF1, and PsXeg1) and an RxLR effector (Pi10232). Using a combined mutagenesis approach, we found that the dual activities of PiAvr3b were tightly linked and determined by 88 amino acids at the C-terminus. We further determined that either the W60 or the E134 residue of PiAvr3b was essential for triggering StR3b-associated HR and inhibiting PiNpp- and Pi10232-associated necrosis, while the S99 residue partially contributed to PTI suppression. Additionally, nuclear localization of PiAvr3b was required to stimulate HR and suppress PTI, but not to inhibit Pi10232-associated cell death. Our study revealed that PiAvr3b suppresses the plant immune response at different subcellular locations and provides an example in which a single amino acid of an RxLR effector links ETI induction and cell death suppression.     

六种疫霉菌体可溶性蛋白质和酯酶的聚丙烯酰胺凝胶平板电泳研究

本文对槐生疫霉(Phytophthora robinicola)、掘氏疫霉(P.drechsleri)、樟疫霉(P.cinnamomi)、烟草疫霉(P.nicotianae)、棕榈疫霉(P.palmivora)及辣椒疫霉(P.capsici)等6种疫霉81株菌菌体可溶性蛋白质和酯酶进行了聚丙烯酰胺凝胶平板电泳研究。结果指出,种间蛋白质图谱差异明显,种内菌株间基本一致。就酯酶图谱来说,种内菌株间存在一定差异,但种间差异更为显著。因此,本试验进一步支持槐生疫霉新种的建立。同时表明,菌体可溶性蛋白质电泳图谱在疫霉种的鉴定和分类上具有重要意义,而酯酶电泳图谱在一定程度上也有助于疫霉种的研究。     

中国疫霉属真菌异宗配合的种的交配型

明确了异宗配合的疫霉属(Phytophthora)7个种(P.capsici,P.cinnamomi,P.drechsleri,P.melonis,P.nicotianae[=P.parasitica],P.palmivora 和 P.sinensis)47个菌株的交配型。特别有意义的是 P.drechsleri A~1和 A~2两个交配型在南京具有相同的优势,并且证实 P.cinnamomi A~1交配型的存在。     

Expressed resistance to black shank among tobacco callus cultures

Summary Quantitatively inherited resistance to the black shank pathogen (Phytophthora parasitica var. nicotianae) was expressed among callus tissue cultures of tobacco (Nicotiana). Tissue cultures of genotypes known to posses polygenic mechanisms for black shank resistance expressed that resistance in vitro when challenged by the viable pathogen. Callus of a susceptible cultivar was readily parasitized in culture. Furthermore, single gene resistance to the common pathogen race was also shown to operate in vitro. Nongenetic factors examined did not contribute significantly to the observed differences. Disease expression in vitro appeared to be highly correlated with its expression at the whole plant level.Screening for quantitative disease resistance can be complicated at the whole plant level by variable hostpathogen reactions and by significant genotype × environment interactions. Since quantitatively inherited mechanisms of black shank resistance are expressed in tobacco callus cultures, an in vitro host-pathogen system may be useful in screening tobacco lines for black shank resistance.The research reported in this paper (No. 82-3-6) is in connection with a project of the Kentucky Agr. Exp. Stn., and the paper is published with the approval of the director     

A proteomics study of in vitro cyst germination and appressoria formation in Phytophthora infestans

A proteomics study using two-dimensional gel electrophoresis (2-DE) and mass spectrometry was performed on Phytophthora infestans. Proteins from cysts, germinated cysts and appressoria grown in vitro were isolated and separated by 2-DE. Statistical quantitative analysis of the protein spots from five independent experiments of each developmental stage revealed significant up-regulation of ten spots on gels from germinated cysts compared to cysts. Five spots were significantly up-regulated on gels from appressoria compared to germinated cysts and one of these up-regulated spots was not detectable on gels from cysts. In addition, one spot was significantly down-regulated and another spot not detectable on the gels from appressoria. The corresponding proteins to 13 of these spots were identified with high confidence using tandem mass spectrometry and database searches. The functions of the proteins that were up-regulated in germinated cysts and appressoria can be grouped into the following categories: protein synthesis (e.g. a DEAD box RNA helicase), amino acid metabolism, energy metabolism and reactive oxygen species scavenging. The spot not detected in appressoria was identified as the P. infestans crinkling- and necrosis-inducing protein CRN2. The identified proteins are most likely involved in the establishment of the infection of the host plant.     

The elicitor-induced oxidative processes in leaves of Solanum species with differential polygenic resistance to Phytophthora infestans

Previous studies have shown that suspension-cultured cells of Solanum genotypes with various polygenic resistances to Phytophthora infestans differed in activities of early oxidative processes in response to culture filtrate (CF) from this pathogen. These studies have now been extended by analysing production of reactive oxygen species (ROS), lipid peroxidation and Lipoxygenase (LOX, E.C.1.13.11.12) activity induced by CF in detached leaves of S. tuberosum cv Bzura and clone H-8105, polygenically resistant and susceptible, respectively, as well as S. nigrum, nonhost, completely resistant. The relative increase in the ROS production was higher in the susceptible clone H-8105 than in both resistant genotypes. Lipid peroxidation increased only in the nonhost S. nigrum. An increase in lipid peroxidation in S. nigrum leaves coincided with enhanced LOX activity. In both S. tuberosum genotypes, significant increases in LOX activity were delayed and unaccompanied by changes in the level of lipid peroxidation. LOX activity attained a higher level in both of the resistant genotypes than in the susceptible one. The present results suggest that the involvement of both ROS production and LOX activity in the defense strategy in Solanum species/P. infestans interactions.     

Rapid identification of Phytophthora ramorum using PCR-SSCP analysis of ribosomal DNA ITS-1

AIMS: The primary objectives of this study were to determine if a single-strand conformation polymorphism (SSCP) analysis can be used for rapid identification of Phytophthora ramorum, an important quarantine plant pathogen worldwide, and to further assess the potential of the SSCP technique as a taxonomic tool for the genus Phytophthora. METHODS AND RESULTS: SSCP of ribosomal DNA internal transcribed spacer 1 was characterized for 12 isolates of P. ramorum, using a recently reported protocol. The SSCP patterns of this species then were compared with those of 18 closely related Phytophthora species. Phytophthora ramorum had a unique pattern and was easily distinguished from genetically, morphologically and ecologically close relatives. CONCLUSION: An immediate benefit of this study is provision of a highly effective and efficient identification tool for P. ramorum in the quarantine process. SIGNIFICANCE AND IMPACT OF THE STUDY: This study also provides additional evidence demonstrating that the SSCP is an ideal DNA marker for species differentiation within the genus Phytophthora.