多聚半乳糖醛酸酶抑制蛋白的结构、功能以及应用研究进展

真菌病害严重影响植物的生长发育。为了自我保护,植物进化出了许多抵御病原真菌入侵的策略,例如防御相关蛋白的产生。多聚半乳糖醛酸酶抑制蛋白（polygalacturonase-inhibiting proteins,PGIPs）是近年来研究较多的一种植物防御蛋白,它能与真菌分泌的多聚半乳糖醛酸酶（polygalacturonases,PGs）特异性结合,降低PGs水解植物细胞壁的活性并在植物体内累积能激活多种防御反应的长链寡聚半乳糖醛酸（oligogalacturonides,OGs）,从而达到抑制真菌侵染的目的。主要介绍了PGIPs的结构、功能及其抗菌机理,并综述了PGIPs在国内外转基因抗病育种中的应用研究进展。     

真菌多聚半乳糖醛酸酶研究进展

真菌多聚半乳糖醛酸酶是降解植物细胞壁果胶的主要降解酶之一,是植物病原真菌的致病因子之一。文中对真菌多聚半乳糖醛酸酶及其序列特征、多聚半乳糖醛酸酶的基因及其序列特征、多聚半乳糖醛酸酶的表达调控以及与病原真菌致病力之间的关系等方面进行了综述。     

通过苜蓿愈伤组织生产植物病害防御蛋白

真菌病原体借助于能降解细胞壁多糖的多聚半乳糖醛酸酶(PG)而侵袭植物。为了抵御病原体的侵害,一些植物组织含有能抑制细胞壁降解生物的PG活性的蛋白(PGIP)。有关PGIP的研究很少,因为,可从植物组织中纯化出来的这种物质有限。     

小麦内切多聚半乳糖醛酸酶抑制蛋白的分离纯化研究

小麦内切多聚半乳糖醛酸酶抑制蛋白的分离纯化研究郑远旗,杨宗剑,李建吾,周立,吴文莲（四川大学生物系,成都６１００６４）余露（中国科学院成都生物研究所,成都６１００４１）关键词内切多聚半乳糖醛酸酶抑制蛋白;内切多聚半乳糖醛酸酶;纯化;小麦内切多聚半乳糖...     

Endo-PG诱导培养小麦细胞PGIP产生的研究

内切多聚半乳糖醛酸酶（endo-polygalacturonase,endo-PG）是待异水解细胞壁成分多聚半乳糖醛酸的酶,水解产生的10～13个糖基的寡聚半乳糖醛酸片段是活性诱导因子,激活植物自身防御系统．我们已研究发现单子叶植物小麦中存在多聚半乳糖醛酸酶抑制蛋白（polygalacturonaseinhibitingprotein,PGIP）,并已将其分离纯化,对其性质作了初步研究[1,2]文献报导[3]PGIP是在未分化的细胞中合成的．本文报导在悬浮培养的小麦细胞中加入Endo-PG观察其PGIP的生成,比较赤霉病的高抗品种与低抗品种中PGIP的合成情况,探讨PGIP与植物防御作…     

真菌果胶酶的分子生物学研究进展

近10年来国外在果胶酶分子生物学研究上取得了重大进展,从11个属的真菌克隆了50个以上的基因并测序。对果胶酶基因的结构、功能、调控、录译后加工等方面进行了深入探讨。已克隆的果胶酶基因以多聚半乳糖醛酸酶(PG)基因和果胶裂解酶(PL)基因为主,也有果胶酯酶(PE)基因和鼠李半乳糖醛酸酶(RHG)基因,大多有内含子。前体蛋白一般有N信号肽和糖基化位点。果胶酶一般受果胶、低浓度的(01%)D半乳糖醛酸等诱导,而受较高浓度(1%)的半乳糖醛酸、抗体、某些抗菌素抑制。     

PGIP在植物抗病方面的研究进展

至今为止,已在20多种植物体内发现了多聚半乳糖醛酸酶抑制蛋白(PGIP)。这类蛋白质主要集中于细胞壁和内膜系统,但在不同生长时间、不同品种及不同器官中其含量是不一样的,研究表明这种差异与植物的抗性强弱有着密切关系。PGIP是病原真菌分泌的endo_PG的抑制剂,因此能延缓病原真菌对植物细胞壁的降解。来自菜豆和小麦的实验证据表明病原真菌侵染植株能诱导pgip基因高水平转录、表达,但pgip基因家族对这种诱导信号应答的分子机制待于进一步研究。     

参与植物天然免疫的LRR型蛋白

植物含有多种富含亮氨酸重复序列(LRRs)结构的蛋白质,它们在植物天然免疫中发挥着重要作用。参与植物防御反应的LRR型蛋白家族包括:类受体蛋白激酶、抗病基因编码蛋白质、多聚半乳糖醛酸酶抑制蛋白和伸展蛋白家族。最近,人们发现植物免疫系统包含:病原相关分子模式(PAMP)激发的免疫性(PTI),即类受体蛋白激酶识别病原菌PAMPs,启动植物防卫反应;病原菌效应子激发的免疫性(ETI),即抗病基因编码蛋白质识别效应子,启动植物防卫反应。除此之外,细胞壁是植物细胞的天然保护屏障。多聚半乳糖醛酸酶抑制蛋白和伸展蛋白通过维护细胞壁,抵御病原菌入侵。我们综述了植物中LRRs蛋白的结构特征与不同种类的LRR蛋白介导免疫反应的分子机制,讨论了LRR型蛋白在植物免疫过程中的意义及存在的问题,指出搜寻配体和下游信号分子将是LRR型蛋白研究热点。     

PGIP在植物抗病方面的研究进展

至今为止,已在２０多种植物体内发现了多聚半乳糖醛酸酶抑制蛋白（ＰＧＩＰ）。这类蛋白质主要集中于细胞壁和内膜系统,但在不同生长时间、不同品种及不同器官中其含量是不一样的,研究表明这种差异与植物的抗性强弱有着密切关系。ＰＧＩＰ是病原真菌分泌的ｅｎｄｏ－ＰＧ的抑制剂,因此能延缓病原真菌对植物细胞壁的降解。来自菜豆和小平的实验证明表明病原真菌侵染植株能诱导ｐｇｉｐ基因高水平转录、表达,但ｐｇｉｐ基因家族对     

真菌果胶酶的分子生物学研究进展

近１０年来国外在果胶酶分子生物学研究上取得了重大进展,从１１个属的真菌克隆了５０个以上的基因并测序。对果胶酶基因的结构、功能、调控、录译后加工等方面进行了深入探讨。已克隆的果胶酶基因以多聚半乳糖醛酸酶（ＰＧ）基因和果胶裂解酶（ＰＬ）基因为主,也有果胶酯酶（ＰＥ）基因和鼠李半乳糖醛酸酶（ＲＨＧ）基因,大多有内含子。前体蛋白一般有Ｎ－信号肽和糖基化位点。果胶酶一般受果胶、低浓度的（０．１％）Ｄ－半乳糖醛酸等诱导,而受较高浓度（１％）的半乳糖醛酸、抗体、某些抗菌素抑制。     

Polygalacturonase-inhibiting proteins in defense against phytopathogenic fungi

Polygalacturonase-inhibiting proteins (PGIPs) are ubiquitous plant cell wall proteins that are directed against fungal polygalacturonases (PGs), which are important pathogenicity factors. The inhibiting activity of PGIPs directly reduces the aggressive potential of PGs. In addition, it causes PGs to form more long-chain oligogalacturonides that are able to induce defense responses, thereby indirectly contributing to the plant defense. Recent evidence demonstrates that PGIPs are efficient defense proteins and limit fungal invasion. PGIPs and the products of many plant resistance genes share a leucine-rich repeat (LRR) structure, which provides specific recognition of pathogen-derived molecules. The high level of polymorphism of both PGIPs and polygalacturonases is an invaluable tool for deciphering the structure, function and evolution of plant LRR proteins and their ligands. Furthermore, information about PGIP structure and evolution paves the way to the development of efficient strategies for crop protection.     

Fungal polygalacturonases exhibit different substrate degradation patterns and differ in their susceptibilities to polygalacturonase-inhibiting proteins.

Polygalacturonic acid (PGA) was hydrolyzed by polygalacturonases (PGs) purified from six fungi. The oligogalacturonide products were analyzed by HPAEC-PAD (high performance anion exchange chromatography-pulsed amperimetric detection) to assess their relative amounts and degrees of polymerization. The abilities of the fungal PGs to reduce the viscosity of a solution of PGA were also determined. The potential abilities of four polygalacturonase-inhibiting proteins (PGIPs) from three plant species to inhibit or to modify the hydrolytic activity of the fungal PGs were determined by colorimetric and HPAEC-PAD analyses, respectively. Normalized activities of the different PGs acting upon the same substrate resulted in one of two distinct oligogalacturonide profiles. Viscometric analysis of the effect of PGs on the same substrate also supports two distinct patterns of cleavage. A wide range of susceptibility of the various PGs to inhibition by PGIPs was observed. The four PGs that were inhibited by all PGIPs tested exhibited an endo/exo mode of substrate cleavage, while the three PGs that were resistant to inhibition by one or more of the PGIPs proceed by a classic endo pattern of cleavage.     

Three aspartic acid residues of polygalacturonase-inhibiting protein (PGIP) from Phaseolus vulgaris are critical for inhibition of Fusarium phyllophilum PG

Polygalacturonase-inhibiting proteins (PGIPs) are plant cell wall proteins that specifically inhibit the activity of endo polygalacturonases (PGs) produced by fungi during the infection process. The interaction with PGIPs limits the destructive potential of PGs and may trigger plant defence responses through the release of elicitor active oligogalacturonides. In order to pinpoint the residues of PvPGIP2 from Phaseolus vulgaris involved in the interaction with PGs, we used site-directed mutagenesis to mutate the residues D131, D157 and D203, and tested for the inhibitory activity of the mutant proteins expressed in Pichia pastoris against Fusarium phyllophilum and Aspergillus niger PGs. Here, we report that mutation of these residues affects the inhibition capacity of PvPGIP2 against F. phyllophilum PG.     

Polygalacturonase inhibiting proteins: players in plant innate immunity?

Polygalacturonase-inhibiting proteins (PGIPs) are extracellular leucine-rich repeat (LRR) proteins that recognize and inhibit fungal polygalacturonases (PGs). The PG-PGIP interaction favours the accumulation of elicitor-active oligogalacturonides and causes the activation of defence responses. Small gene families encode PGIP isoforms that differ in affinity and specificity for PGs secreted by different pathogens. The consensus motif within the LRR structure of PGIPs is the same as that of the extracellular receptors of the plant innate immune system. Structural and functional evidence suggest that PGIPs are versatile proteins involved in innate immunity and that they are capable of recognizing different surface motifs of functionally related but structurally variable PGs.     

Polygalacturonases, polygalacturonase-inhibiting proteins and pectic oligomers in plant-pathogen interactions

Polygalacturonases (PGs) are produced by fungal pathogens during early plant infection and are believed to be important pathogenicity factors. Polygalacturonase-inhibiting proteins (PGIPs) are plant defense proteins which reduce the hydrolytic activity of endoPGs and favor the accumulation of long-chain oligogalacturonides (OGs) which are elicitors of a variety of defense responses. PGIPs belong to the superfamily of leucine reach repeat (LRR) proteins which also include the products of several plant resistance genes. A number of evidence demonstrates that PGIPs efficiently inhibit fungal invasion.     

Plants use identical inhibitors to protect their cell wall pectin against microbes and insects

As fundamentally different as phytopathogenic microbes and herbivorous insects are, they enjoy plant‐based diets. Hence, they encounter similar challenges to acquire nutrients. Both microbes and beetles possess polygalacturonases (PGs) that hydrolyze the plant cell wall polysaccharide pectin. Countering these threats, plant proteins inhibit PGs of microbes, thereby lowering their infection rate. Whether PG‐inhibiting proteins (PGIPs) play a role in defense against herbivorous beetles is unknown. To investigate the significance of PGIPs in insect–plant interactions, feeding assays with the leaf beetle Phaedon cochleariae on Arabidopsis thaliana pgip mutants were performed. Fitness was increased when larvae were fed on mutant plants compared to wild‐type plants. Moreover, PG activity was higher, although PG genes were downregulated in larvae fed on PGIP‐deficient plants, strongly suggesting that PGIPs impair PG activity. As low PG activity resulted in delayed larval growth, our data provide the first in vivo correlative evidence that PGIPs act as defense against insects.     

Antisense expression of the Arabidopsis thaliana AtPGIP1 gene reduces polygalacturonase-inhibiting protein accumulation and enhances susceptibility to Botrytis cinerea

Polygalacturonases (PGs) hydrolyze the homogalacturonan of plant cell-wall pectin and are important virulence factors of several phytopathogenic fungi. In response to abiotic and biotic stress, plants accumulate PG-inhibiting proteins (PGIPs) that reduce the activity of fungal PGs. In Arabidopsis thaliana, PGIPs with comparable activity against BcPG1, an important pathogenicity factor of the necrotrophic fungus Botrytis cinerea, are encoded by two genes, AtPGIP1 and AtPGIP2. Both genes are induced by fungal infection through different signaling pathways. We show here that transgenic Arabidopsis plants expressing an antisense AtPGIP1 gene have reduced AtPGIP1 inhibitory activity and are more susceptible to B. cinerea infection. These results indicate that PGIP contributes to basal resistance to this pathogen and strongly support the vision that this protein plays a role in Arabidopsis innate immunity.     

Polygalacturonase-inhibiting protein (PGIP) in plant defence: a structural view

Polygalacturonase-inhibiting proteins are plant extracellular leucine-rich repeat proteins that specifically bind and inhibit fungal polygalacturonases. The interaction with PGIP limits the destructive potential of polygalacturonases and might trigger the plant defence responses induced by oligogalacturonides. A high degree of polymorphism is found both in PGs and PGIPs, accounting for the specificity of different plant inhibitors for PGs from different fungi. Here, we review the structural features and our current understanding of the PG-PGIP interaction.