Frontiers in plant–microbe interactions: part 1

In marginal, nutrient poor forest soils, the roots of dominant tree species enter into mutually beneficial, nutrient acquiring interactions with ectomycorrhizal (ECM) fungi. Despite the inherent benefit to the plant, the molecular events that underpin these interactions remain poorly understood. One of the main aspects studied to date regarding the controls of these symbioses include how plant immunity is modulated during the ingrowth of fungi into plant roots. While effector-like proteins and microRNAs (miRNAs) are well known to regulate pathogenic plant-microbe interactions, significantly fewer signalling molecules used to foster mutualistic symbioses by ectomycorrhizal (ECM) fungi have been characterized. ECM fungi, on an evolutionary timescale, are a relatively recent class of symbiotic organisms having evolved from saprotrophic fungi ~270 MYA. As their ancestral lifestyle did not interact with live plants, convergent evolution may have led to mechanisms in ECM fungi that enable them to enter into symbiosis with plants in a similar manner to pathogenic microbes. Using the model interaction between the forest tree Eucalyptus grandis and the mutualistic ECM fungus Pisolithus microcarpus we have been investigating the role of these two classes of signature signals during the establishment of symbiosis. I will cover our recent characterization of several effector-like ‘Mycorrhiza-Induced Small Secreted Proteins’ (MiSSPs) and fungal miRNAs during the mutualistic interaction with E. grandis. Using sequencing, in situ localization, and mutagenic work we demonstrate that both classes of microbial signals have the capacity to directly alter host metabolism and hormone perception, pathways integral to the plant immune system during microbial challenge. Altogether, our work is providing new evidence of cross-kingdom communication between ECM fungi and plant roots that was previously undescribed, shedding light on how this relatively recent lifestyle has convergently evolved pathways to pathogenic microbes during host colonization.

Biography

Associate Prof. Jonathan Plett did his doctoral work at Queen’s University in Canada followed by a post doctoral research position at L’Institut National de la Recherche Agronomique (INRA; France) in Dr. Francis Martin’s group. Jonathan is now a faculty member of the Hawkesbury Institute for the Environment at Western Sydney University in Australia. Jonathan is a pioneer in decoding the genetic basis enabling plants to form symbiotic relationships with beneficial rather than pathogenic microbes. Mycorrhizal fungi are among the most important microbes that form beneficial symbiotic interactions and are essential for sustainability and productivity of plant life in natural and managed ecosystems world-wide. Outcomes of this research are important for screening new tree lines to find the ‘sweet spot’ in immune defence that enables plants to maximise benefits from mycorrhizal fungi without compromising disease resistance. These results will result in more productive tree plantations.

Root endophytic fungi (EF) play a crucial role in root guilds and have gathered increasing attention due to their diverse ecological functions and flexible lifestyles. The establishment of mutualistic symbioses with fungal endophytes across various lineages often enhances plant fitness, including growth and adaptation. The ‘symbiosis triangle’ hypothesis emphasizes the significance of environmental factors in regulating the outcomes of these symbiotic interactions. In this seminar, I will present prime examples that illustrate how soil nutrients and salt stress influence the behavior of endophytes at both the physiological and genomic scales.

Studies have demonstrated that variations in external nutrient levels or forms can lead to extensive physiological remodeling in fungi. These adaptations encompass changes in nutrient transporters, lipid metabolism, secondary metabolite biosynthesis, and plant-cell-wall-degradation enzymes. These changes contribute, at least in part, to the maintenance and erosion of symbiotic relationships. Furthermore, recent findings indicate that certain populations of EF undergo population divergence arising from positive selection of genomic islands and chromosome polymorphisms, including ploidy changes, in response to natural soil saline conditions. We propose that hybridization accompanied by doubling ploidy allows EF to generate phenotypic novelty and drive genome evolution for saline adaptation. Notably, allodiploid EF strains exhibit increased vigor under a range of abiotic stresses, which suggests the potential of using allodiploid EF isolates to improve plant salt tolerance.

By gaining a better understanding on how environment conditions impact EF physiology and genome evolution, we can establish a new framework to enhance the symbiotic efficiency of EF, and ultimately benefiting host plants and their fitness.

Biography

Dr. Zhilin Yuan is a distinguished professor at Chinese Academy of Forestry. In 2002 and 2005, he obtained his bachelor’s and master’s degrees from Nanjing Normal University. In 2010, he got the Ph. D degree of plant pathology from Zhejiang University. Since 2005, he has been affiliated with Research Institute of Subtropical Forestry, Chinese Academy of Forestry. In addition, he served as a guest staff member in the Department of Life Sciences (Division II: Forestry and Ecology) of National Science Foundation of China (NSFC) from January to October 2018. Dr. Yuan visited Duke University, Technische Universität Wien, Auburn University, and Institute of Microbiology, Czech National Academy of Sciences for academic exchanges between 2012-2016.

Presently, Dr. Yuan holds the position of Principal Investigator at the State Key Laboratory of Tree Genetics and Breeding and he is also a member of the Professional Committee on Forest Soils of Soil Science Society of China. His main research interests focus on tree–fungus symbioses and genetic and environmental control of their interactions. Dr. Yuan has an impressive publication record, with over 20 articles published in prestigious journals including the ISME Journal, Biotechnol Adv, Curr Biol, Plant Cell Environ, and Appl Environ Microbiol.

In recognition of his contributions, he has received numerous awards and honors. He was honored as the Excellent Youth of Chinese Academy of Forestry in 2014, the 2nd level training personnel of the ‘151’ Talent Project of Zhejiang Province in 2015, the 14th Youth Award of Science and Technology of Chinese Forestry in 2017, and he is also the recipient of the ‘Hundred Million’ Talent Project of the State Forestry and Grassland Administration. He hosted the Youth Fund, General Fund and Outstanding Youth Fund of NSFC.

Upon perception of rhizobial signal by Nod factor receptors, NF signaling is activated to initiate rhizobial infection and nodule organogenesis. In soybean, we have identified a core molecular module GmNINa-miR172c-NNC1 that coordinates these processes during nodulation. The essential nodulation regulator GmNINa is induced by rhizobia, and then activates miR172c transcription. miR172c cleaves the mRNA of its target gene NNC1, which encodes a nodulation repressor of the nodulation genes, such as ENOD40, resulting in rhizobial infection and organogenesis. In addition, we show that this module also activates autoregulation of nodulation (AON) through a double secured mechanism to ensure nodulation is systemically controlled. Furthermore, we show that AON suppresses further nodulation by attenuating the function of GmNINa-miR172c-NNC1 module through a B-type cytokinin response factor GmRR11d. GmRR11d is induced by rhizobia and represses GmNINa by directly binding to GmNIN promoter and inhibiting transcriptional activity of GmNSP1a on GmNINa in a GmNARK-dependent manner. Thus, we have constructed a regulatory network involved in nodulation in soybean.

Biography

I obtained my Ph.D. degree from Purdue University in 2001. Then I joined Vector Tobacco Inc. as a research scientist for three years. From 2004, I worked as a PI in Institute of Genetics and Developmental Biology (IGDB) with the support of “one hundred talents” program of Chinese Academy of Sciences. My research interest includes plant adaptation to environmental conditions such as salt stress and nitrogen deficiency. In 2015, I joined Huazhong Agricultural University as a distinguished profess with the research focus on genetic basis of symbiotic nitrogen fixation with ultimate goal to genetically improve symbiotic nitrogen fixation efficiency and yield of soybean.