Department of Life Sciences and Systems Biology, University of Turin, Viale Mattioli 25, 10125 Turin, Italy.
National Research Council, Institute for Sustainable Plant Protection, Viale Mattioli 25, 10125 Turin, Italy.
Int J Mol Sci. 2020 Apr 29;21(9):3139. doi: 10.3390/ijms21093139.
Photosynthetic orchids associate with mycorrhizal fungi that can be mostly ascribed to the "rhizoctonia" species complex. Rhizoctonias' phylogenetic diversity covers a variety of ecological/nutritional strategies that include, beside the symbiosis establishment with host plants, endophytic and pathogenic associations with non-orchid plants or saprotrophic soil colonization. In addition, orchid mycorrhizal fungi (OMF) that establish a symbiotic relationship with an orchid host can later proliferate in browning and rotting orchid tissues. Environmental triggers and molecular mechanisms governing the switch leading to either a saprotrophic or a mycorrhizal behavior in OMF remain unclear. As the sequenced OMF genomes feature a wide range of genes putatively involved in the degradation of plant cell wall (PCW) components, we tested if these transitions may be correlated with a change in the expression of some PCW degrading enzymes. Regulation of several genes encoding PCW degrading enzymes was evaluated during saprotrophic growth of the OMF on different substrates and under successful and unsuccessful mycorrhizal symbioses. Fungal gene expression was investigated in two orchid species, the terrestrial Mediterranean and the epiphytic tropical . Although we only tested a subset of the CAZyme genes identified in the genome, and we cannot exclude therefore a role for different CAZyme families or members inside a family, the results showed that the degradative potential of is finely regulated during saprotrophic growth and in symbiosis, often with a different regulation in the two orchid species. These data pose novel questions about the role of fungal PCW degrading enzymes in the development of unsuccessful and successful interactions.
光合兰与菌根真菌共生，这些菌根真菌主要属于“立枯丝核菌”种复合体。立枯丝核菌的系统发育多样性涵盖了多种生态/营养策略，除了与宿主植物建立共生关系外，还与非兰科植物的内生和病原性关联以及腐生土壤定殖有关。此外，与兰花宿主建立共生关系的兰花菌根真菌（OMF）随后可以在兰花组织的褐变和腐烂中增殖。控制导致 OMF 向腐生或菌根行为转变的环境触发因素和分子机制尚不清楚。由于测序的 OMF 基因组具有广泛的可能参与降解植物细胞壁（PCW）成分的基因，我们测试了这些转变是否与某些 PCW 降解酶表达的变化相关。在不同基质上的腐生生长和成功和不成功的菌根共生条件下，评估了 OMF 中编码 PCW 降解酶的几个基因的表达调控。在两个兰花物种中，陆生地中海和附生热带，研究了真菌基因表达。尽管我们仅测试了 基因组中鉴定的 CAZyme 基因的一个子集，因此不能排除不同 CAZyme 家族或家族内的不同成员的作用，但结果表明，在腐生生长和共生中，的降解潜力受到精细调控，在两种兰花物种中通常具有不同的调控。这些数据提出了关于真菌 PCW 降解酶在不成功和成功相互作用发展中的作用的新问题。
