Beneficial fungi are widespread and form associations with over 90% of terrestrial plant species; therefore, they play an essential role in global agro-ecology. However, in natural ecosystems, plants are often subjected to some environmental factors that have a variety of influences on plant-fungi interactions and the degree of mutual benefits. Nitrogen (N) is a dominant element in determining the carbohydrate composition and metabolism of plants in terrestrial ecosystems. However, beneficial plant-fungi interactions are largely regulated by the external N status. The mechanisms by which N application regulates plant-beneficial fungi associations have rarely been investigated.
Recently, the team led by Prof. Chuan-Chao Dai from the College of Life Sciences, Nanjing Normal University has published their findings entitled “Nitrogen fertilizer-regulated plant-fungi interaction is related to root invertase-induced hexose generation” in the FEMS Microbiology Ecology (https://doi.org/10.1093/femsec/fiaa139).
The accessible carbohydrate sinks in roots influence the colonization and degree of mutual benefit provided by root fungal symbionts. Using rice-Phomopsis liquidambaris (a root endophyte) symbiotic system, the researchers found that soluble acid invertases in rice root were activated, resulting in increased hexose fluxes in inoculated roots. These fluxes positively influenced fungal colonization, especially under N-deficient conditions. Further experiments manipulating the carbohydrate composition and root invertase activity through sugar feeding, chemical treatments and the use of different soil types revealed that the external disturbance of root invertase could reduce endophytic colonization and eliminate endophyte-induced host benefits under N-deficient conditions. Therefore, certain combinations of farmland ecosystems with suitable N inputs could be implemented to maximize the benefits of plant-fungi associations.
Prof. Chuan-Chao Dai from Nanjing Normal University is the corresponding author. Kai Sun and Wei Zhang from the College of Life Sciences are joint first authors. This work was financially supported by the the National Nature Science Foundation of China (NSFC NO. 31570491) and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
A proposed model in which root invertase and hexose generation is involved in N-regulated mutualistic colonization by the fungus Phomopsis liquidambaris. (a) The proposed pathway of the optimal N input within the N-deficient range for endophytic colonization in plant roots. Host plants tend to build a suitable C sink for root endophyte development, which is triggered by N-deficient conditions. The effects of this pathway, however, decreased with the increased N levels. As thus, in the optimal N condition, (b) root invertase activity is activated and involved in the generation of hexose for endophyte growth, which, however, could be affected by soil conditions or other environmental factors.