(665b) Genetic Mechanisms Enabling Fast Biomass Decomposition in Brown Rot Wood-Decaying Fungi

Fungi are dominant microbes for plant biomass degradation in terrestrial system. Some of them, namely brown rot fungi, evolved more efficient mechanisms than others, causing the fast decomposition and utilization of woody biomass. The efficacy in carbon conversion of brown rot fungi make them the great resource for discovering toolkits for industrial application of lignocellulosic biomass. Similar brown rot lifestyles have been convergently evolved from multiple independent fungal lineages, especially in Agaricomycotina subphylum that contains most of wood-decaying fungi, suggesting consensus genetic bases may have been adapted by different brown rot fungi. This adaption has been explained, to some extent, by the losses and shrinkages of the lignin- and cellulose-degrading genes compared to other white rot ancestral fungi. These genes losses have most likely facilitated brown rot fungi to more selectively target carbohydrates rather than simultaneously degrade all lignocellulose components as in white rot. But, the massive gene losses (> 65% CAZY loss) did not convincingly explain the ‘gain’ of a fast decomposing ability of brown rot, indicating other key parts of brown rot system were still missed in current understandings. Using functional genomics, we recently found that gene regulation shifts have contributed to brown rot adaption by 1) staggering the expression of oxidoreductases ahead of hydrolytic enzymes, and 2) strengthening the cellular invest on the retained brown rot CAZY gene repertories. Key brown rot pathways were ‘dug out’ by these comparative studies. These, together, have since enabled us to propose a new 'two-step' model to explain the genetic mechanisms of brown rot adaptation. Recently, we are conducting a more extensive functional genomic comparison by sampling more representative wood decay species, to further understand the genetic forces driving the occurrence of brown rot adaptation. Meanwhile, our recent efforts are also being invested to build the gene editing platform in brown rot fungi to genetically test our brown rot model revealed by system biology tools.