Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, SE-75007, Uppsala, Sweden.
Research division of Biochemical Technology, Institute of Chemical, Environmental and Biological Engineering, Vienna University of Technology, Gumpendorferstrasse 1a, 1060, Vienna, Austria.
BMC Microbiol. 2018 Nov 7;18(1):178. doi: 10.1186/s12866-018-1310-9.
Pectin is one of the major and most complex plant cell wall components that needs to be overcome by microorganisms as part of their strategies for plant invasion or nutrition. Microbial pectinolytic enzymes therefore play a significant role for plant-associated microorganisms and for the decomposition and recycling of plant organic matter. Recently, comparative studies revealed significant gene copy number expansion of the polysaccharide lyase 1 (PL1) pectin/pectate lyase gene family in the Clonostachys rosea genome, while only low numbers were found in Trichoderma species. Both of these fungal genera are widely known for their ability to parasitize and kill other fungi (mycoparasitism) and certain species are thus used for biocontrol of plant pathogenic fungi.
In order to understand the role of the high number of pectin degrading enzymes in Clonostachys, we studied diversity and evolution of the PL1 gene family in C. rosea compared with other Sordariomycetes with varying nutritional life styles. Out of 17 members of C. rosea PL1, we could only detect two to be secreted at acidic pH. One of them, the pectate lyase pel12 gene was found to be strongly induced by pectin and, to a lower degree, by polygalacturonic acid. Heterologous expression of the PEL12 in a PL1-free background of T. reesei revealed direct enzymatic involvement of this protein in utilization of pectin at pH 5 without a requirement for Ca. The mutants showed increased utilization of pectin compounds, but did not increase biocontrol ability in detached leaf assay against the plant pathogen Botrytis cinerea compared to the wild type.
In this study, we aimed to gain insight into diversity and evolution of the PL1 gene family in C. rosea and other Sordariomycete species in relation to their nutritional modes. We show that C. rosea PL1 expansion does not correlate with its mycoparasitic nutritional mode and resembles those of strong plant pathogenic fungi. We further investigated regulation, specificity and function of the C. rosea PEL12 and show that this enzyme is directly involved in degradation of pectin and pectin-related compounds, but not in C. rosea biocontrol.
果胶是植物细胞壁的主要成分之一，也是最复杂的成分之一，微生物需要将其分解，这是其入侵或获取植物营养的策略的一部分。因此，微生物果胶酶在与植物相关的微生物以及植物有机物质的分解和再循环中发挥着重要作用。最近的比较研究表明，在 Clonostachys rosea 基因组中，多糖裂解酶 1（PL1）果胶/果胶裂解酶基因家族的基因拷贝数显著扩张，而在 Trichoderma 物种中则发现数量较低。这两个真菌属都因其能够寄生和杀死其他真菌（真菌寄生）的能力而广为人知，某些物种因此被用于植物病原真菌的生物防治。
为了了解果胶降解酶数量众多在 Clonostachys 中的作用，我们研究了 C. rosea 与具有不同营养生活方式的其他 Sordariomycetes 相比，PL1 基因家族的多样性和进化。在 C. rosea 的 17 个 PL1 成员中，我们只能检测到两个在酸性 pH 下被分泌。其中之一，果胶裂解酶 pel12 基因被发现能被果胶强烈诱导，而被多聚半乳糖醛酸诱导的程度较低。在缺乏 PL1 的 T. reesei 背景下异源表达 PEL12 表明，该蛋白直接参与了在 pH 5 下利用果胶，而不需要 Ca。与野生型相比，突变体显示出对果胶化合物利用的增加，但在离体叶片测定中对植物病原菌 Botrytis cinerea 的生物防治能力没有增加。
在这项研究中，我们旨在深入了解 C. rosea 和其他 Sordariomycete 物种中 PL1 基因家族的多样性和进化与其营养模式的关系。我们表明，C. rosea PL1 的扩张与它的真菌寄生营养模式无关，而与强植物病原真菌相似。我们进一步研究了 C. rosea PEL12 的调节、特异性和功能，表明该酶直接参与了果胶和果胶相关化合物的降解，但不参与 C. rosea 的生物防治。
