微生物诱导的植物系统抗性

综述了由植物病原菌和非病原性的根际促生菌诱导产生的两种植物系统抗性:系统获得性抗性(SAR)和系统诱导抗性(ISR),比较了两类系统抗性的诱导、信号分子和机理的异同点,阐述了信号分子水杨酸在系统获得性抗性诱导过程中的作用及茉莉酸和乙烯在系统诱导抗性产生过程中的作用。     

An Arabidopsis callose synthase

-1,3-glucan polymers are major structural components of fungal cell walls, while cellulosic -1,4-glucan is the predominant polysaccharide in plant cell walls. Plant -1,3-glucan, called callose, is produced in pollen and in response to pathogen attack and wounding, but it has been unclear whether callose synthases can also produce cellulose and whether plant cellulose synthases may also produce -1,3-glucans. We describe here an Arabidopsis gene, AtGsl5, encoding a plasma membrane-localized protein homologous to yeast -1,3-glucan synthase whose expression partially complements a yeast -1,3-glucan synthase mutant. AtGsl5 is developmentally expressed at highest levels in flowers, consistent with flowers having high -1,3-glucan synthase activities for deposition of callose in pollen. A role for AtGsl5 in callose synthesis is also indicated by AtGsl5expression in the Arabidopsis mpk4 mutant which exhibits systemic acquired resistance (SAR), elevated -1,3-glucan synthase activity, and increased callose levels. In addition, AtGsl5 is a likely target of salicylic acid (SA)-dependent SAR, since AtGsl5mRNA accumulation is induced by SA in wild-type plants, while expression of the nahG salicylate hydroxylase reduces AtGsl5 mRNA levels in the mpk4 mutant. These results indicate that AtGsl5is likely involved in callose synthesis in flowering tissues and in the mpk4 mutant.     

Abscisic acid modulates salicylic acid biosynthesis for systemic acquired resistance in tomato

Among the regulatory mechanisms of systemic acquired resistance (SAR) in tomato, antagonistic interaction between salicylic acid (SA) and abscisic acid (ABA) signaling pathways was investigated. Treatment with 1,2-benzisothiazol-3(2H)-one1,1-dioxide (BIT) induced SAR in tomato thorough SA biosynthesis. Pretreatment of ABA suppressed BIT-induced SAR including SA accumulation, suggesting that ABA suppressed SAR by inhibiting SA biosynthesis.     

Induction of Systemic Acquired Resistance by Heat Shock Treatment in Arabidopsis

A 3,6-di-O-benzylated demethylallosamizoline derivative was glycosylated at the 4-position with an N, N′-diphthaloylchitobiosyl moiety by using the thioglycoside method. After de-protections, the resulting demethylallosamidin-like pseudotrisaccharide was evaluated as an inhibitor against a couple of chitinases.     

Reduced toxicity and broad spectrum resistance to viral and fungal infection in transgenic plants expressing pokeweed antiviral protein II

Pokeweed antiviral protein II (PAPII), a 30 kDa protein isolated from leaves of Phytolacca americana, inhibits translation by catalytically removing a specific adenine residue from the large rRNA of the 60S subunit of eukaryotic ribosomes. The protein sequence of PAPII shows only 41% identity to PAP and PAP-S, two other antiviral proteins isolated from pokeweed. We isolated a cDNA corresponding to PAPII and introduced it into tobacco plants. PAPII expressed in transgenic tobacco was correctly processed to the mature form as in pokeweed and accumulated to at least 10-fold higher levels than wild-type PAP. We had previously observed a significant decrease in transformation frequency with PAP and recovered only two transgenic lines expressing 1–2 ng per mg protein. In contrast, eight different transgenic lines expressing up to 250 ng/mg PAPII were recovered, indicating that PAPII is less toxic than PAP. Two symptomless transgenic lines expressing PAPII were resistant to tobacco mosaic virus, potato virus X and the fungal pathogen Rhizoctonia solani. The level of viral and fungal resistance observed correlated well with the amount of PAPII protein accumulated. Pathogenesis-related protein PR1 was constitutively expressed in transgenic lines expressing PAPII. Although PR1 was constitutively expressed, no increase in salicylic acid levels was detected, indicating that PAPII may elicit a salicylic acid-independent signal transduction pathway.     

Expression of tobacco class II catalase gene activates the endogenous homologous gene and is associated with disease resistance in transgenic potato plants

We have previously shown that healthy potato plants respond poorly to salicylic acid (SA) for activating disease resistance against the late blight fungal pathogen Phytophthora infestans. However, SA is essential for the establishment of potato systemic acquired resistance (SAR) against P. infestans after treatment with the fungal elicitor arachidonic acid (AA). To understand the molecular mechanisms through which AA induces SA-dependent SAR in potato, we have recently studied the expression of potato class II catalase (Cat2St) in comparison with its tobacco homologue, Cat2Nt, which has previously been shown to bind SA. In the present study, we show that tobacco Cat2Nt is expressed at high levels and accounts for almost half of total SA-binding activity detected in tobacco leaves. In contrast, potato Cat2St is not expressed in healthy leaves, which is associated with the low SA responsiveness of potato plants for activation of disease resistance mechanisms. Upon treatment with AA, expression of potato Cat2St is induced not only in AA-treated leaves, but also in the upper untreated parts of the plants, concomitant with the establishment of SA -dependent SAR to P. infestans. Moreover, expression of the tobacco Cat2Nt gene in transgenic potato plants leads to constitutive expression of the endogenous potato Cat2St gene and is associated with enhanced resistance to P. infestans. These results collectively indicate that plant SA-binding class II catalases may play an important role in the development of disease resistance, possibly by serving as biological targets of SA.     

Salicylic acids: Local,systemic or inter-systemic regulators?

Salicylic acid is well known phytohormone, emerging recently as a new paradigm of an array of manifestations of growth regulators. The area unleashed yet encompassed the applied agriculture sector to find the roles to strengthen the crops against plethora of abiotic and biotic stresses. The skipped part of integrated picture, however, was the evolutionary insight of salicylic acid to either allow or discard the microbial invasion depending upon various internal factors of two interactants under the prevailing external conditions. The metabolic status that allows the host invasion either as pathogenesis or symbiosis with possible intermediary stages in close systems has been tried to underpin here.     

高等植物病原相关蛋白

在过去的三十年中,人们对诱导系统性抗性——这一普遍存在于高等植物抗病过程中的现象——进行了深入研究。被真菌、细菌或病毒侵染后,植物表现出广泛的、长时间的系统性抗性。在这一过程中,植物细胞壁组成成分发生改变,表达各种病原相关蛋白(PR蛋白),并合成多种植物抗毒素。本文就主要的PR蛋白家族的结构和功能特性,PR蛋白的发现和分类,及PR蛋白的应用作一综述。     

Induced systemic resistance (ISR) against pathogens in the context of induced plant defences

Induced systemic resistance (ISR) of plants against pathogens is a widespread phenomenon that has been intensively investigated with respect to the underlying signalling pathways as well as to its potential use in plant protection. Elicited by a local infection, plants respond with a salicylic-dependent signalling cascade that leads to the systemic expression of a broad spectrum and long-lasting disease resistance that is efficient against fungi, bacteria and viruses. Changes in cell wall composition, de novo production of pathogenesis-related-proteins such as chitinases and glucanases, and synthesis of phytoalexins are associated with resistance, although further defensive compounds are likely to exist but remain to be identified. In this Botanical Briefing we focus on interactions between ISR and induced resistance against herbivores that is mediated by jasmonic acid as a central signalling molecule. While many studies report cross-resistance, others have found trade-offs, i.e. inhibition of one resistance pathway by the other. Here we propose a framework that explains many of the thus far contradictory results. We regard elicitation separately from signalling and from production, i.e. the synthesis of defensive compounds. Interactions on all three levels can act independently from each other.