Seogchan Kang Outlines Project
Posted: December 18, 2015
Fertilizers and pesticides represent one of the pillars that have sustained the Green Revolution. However, heavy reliance on their use has created major environmental problems, intensifying the call for more diverse strategies to help meet the steadily growing global need for quality food and feed without further damaging the environment. I believe such strategies can be found via better understanding of how plants have evolved with diverse communities of microbes. Despite critical roles of diverse plant-associated microbes in plant fitness and niche adaption, current strategies for crop production mostly neglect microbial partners and microbial processes underpinning their benefits to plants and may even unknowingly destroy critical partnerships, rendering plants heavily dependent on chemical input for health and productivity. Deployment of microbes that can assist plants in coping with biotic and abiotic stress and efficiently acquiring key nutrients has been promoted. However, their adoption has been rather limited due to several problems, most of which resulted from limited knowledge about how such microbes interact with plants and the environment.
A main focus in my laboratory has been to discover molecules that mediate plant-microbe interactions and characterize their mechanisms of action. Through evolutionary arms races and alliances, both plants and microbes have invented a bewildering array of strategies to fight and communicate with the other side. One such strategy is to secrete proteins, metabolites and even RNAs that affect other organisms. My laboratory has focused on the discovery and characterization of volatile organic compounds (VOCs) that affect plant physiology and development. Some may wonder why VOCs. Here is why:
Fig. 1. Known and hypothesized roles of VOCs in mediating organismal interactions. The double-headed arrows denote various types of VOC–mediated organismal interaction. Anthropogenic and biogenic VOCs enter the surrounding atmosphere, affecting the environmental quality and ecosystem health. Soils function as both sources and sinks of VOCs. Certain VOCs produced by Plant Growth-Promoting Rhizobacteria (PGPR) induce plant growth and stress resistance. This diagram came from a review our lab published (Bitas et al., 2013. Sniffing on microbes: Diverse roles of microbial volatile organic compounds in plant health. Mol. Plant-Microbe Interactions, 26:835–843).
As illustrated in Fig.1, organisms in multiple kingdoms have evolved to use VOCs as signals for intra- and inter-species interactions. Considering their ability to travel far from the point of production through multiple media (e.g., air, liquids, porous soils), their involvement in both short- and long-distance organismal interactions is not too surprising. In fact, without semio-VOCs, the shape and function of the biosphere would look very different. Critical roles of animal- and plant-derived VOCs in directing animal behaviors (e.g., pheromones, volatile cues to pollinators, parasitoids and biting insects) and volatile hormones as a language for plant-to-plant communication (e.g., methyl jasmonate, methyl salicylate) have been well documented. There also exists evidence suggesting the involvement of microbial VOCs in antagonism, mutualism, and intra- and inter-species regulation of cellular and developmental processes. However, studies on how microbial VOCs affect microbial interactions with other organisms, microbial niche adaptation, and eventually ecosystem functions have been quite limited. Given the ubiquitous presence of microbes and diverse and critical roles they, and their products, play in animal/human health and agro- and natural-ecosystem functions, this knowledge gap should be filled.
Fig. 2. Plant growth promotion by Fusarium oxysporum VOCs. Shoot fresh weight of Nicotiana tabacum was measured after two weeks of cocultivation with no fungus (control), F. oxysporum strains NRRL 38499, NRRL 26379, and NRRL 38335. Representative plates are shown in the insert. The center divider of I plate prevents physical contact between plants and fungi. This figure came from Bitas et al., (2015 Frontiers in Microbiology 6:1248).
Our work with multiple species of root-associated fungi has shown the involvement of yet-to-be-identified VOCs in controlling plant growth and stress resistance (e.g., Fig. 2). We have been using a combination of genomics, genetics, and biochemistry to identify the nature of such compounds and to characterize how they affect plant growth and stress resistance. If you want to learn more about our work on fungal VOCs, please read the review mentioned above as well as a paper by Bitas et al. (2015 Frontiers in Microbiology 6:1248).
As research on proteins that mediate plant-microbe interactions has resulted in multiple crop protection strategies, identification and characterization of semio-VOCs will also likely yield handsome bounties (e.g., judicious uses of beneficial microbes, effective control of pathogens and abiotic stress by enhancing plant fitness, new targets for breeding or genetic engineering to improve key agronomic traits). Our research on fungal VOCs has been supported by funds from the Penn State College of Agricultural Sciences (Jeanne & Charles Rider Endowment and Strategic Collaboration Seed Grant), as well as awards to my student Ningxiao Li, Ph.D. candidate in Plant Biology (summer support from the Penn State Center for Environment geoChemistry & Genomics, the Storkan-Hanes-McCaslin Research Foundation Award, and the 2015 Huck Dissertation Research Award). Other participants in this project include Dr. Vasileios Bitas, a recent Ph.D. student from my lab, Dr. Jim Tumlinson, Director of the Penn State Center for Chemical Ecology, and Dr. Kathy Brown, Professor of Plant Physiology.