Spatiotemporal Dynamics Of Stomatal Oscillations Inducing By Microbes-Foliar Microenvironment Interactions And Its Mechanisms

Stomata, natural openings for carbon assimilation and transpiration in the leaves of terrestrial plants, can also serve as portals for the invasions of various pathogens. However, rapid active stomatal closure could cut off the bacterial penetrations by recognizing of the Pathogen Associated Molecular Patterns. In the natural environment, the leaf surfaces are coated by layers of microorganisms. Many of them are non-pathogenic bacteria, but little is known about their regulatory role on stomatal behavior. On the other hand, the stomatal movements are simutaneously regulated by light, leaf temperature, air humidity and atmospheric CO2 concentration. So, do these environmental factors influence the efficacy of stomatal immunity? In another word, do stomata close irreversibly? If yes, do the plants become "weaker" because of constant stomatal closure? Based on the principles of Microbial Ecology, Stomatal biology and Photosynthetic physiology, we hypothesize that the interactions between micro-environmental factors and foliar bacteria could induce collective stomatal oscillations across the leaf blade. More specifically, we reason that the leaf photosynthesis and immune response are competing with each other. Such competitions would cause stomatal oscillations temporally and patchy stomatal conductance, spatially. The spatial patterns, periods and amplitudes of the oscillations are also determined by the intensities and durations of these biotic and abiotic factors. To testify this hypothesis, we selected Broad bean (Vicia faba L.) and non—plant pathogenic strain Escherichia. coil as material. Direct microscopic observation, chlorophyll fluorescence imaging, gas exchange measurement, laser scanning co-focal microscopy and artificial environmental manipulations were performed to investigate the spatiotemporal feature of immune collective stomatal oscillation and thus develop new approaches to cut excessive leaf transpiration. The results showed:(1) Stomatal immunity is a collective behavior:leaf inoculation of E. coli induced rapid stomatal closure both in the epidermal strips and in intact leaves. Stomata oscillated and closed collectively in and 300-600μm away from the inoculation locus. The intensity of stomatal immunity is correlated with the bacterial location and its population size.(2) The competition between micro-environmental factors and foliar bacteria trigger evident stomatal oscillation and patchy stomatal conductance across the leaf blade. The amplitude, period and spatial pattern of the oscillation are modulated by light, air humidity, soil water status and atmospheric CO2 concentration.(3) Immune collective stomatal oscillations overlap with ABA signaling. Genes like ABIl, Atrboh D and FLS2, are involved in the PAMP-induced stomatal closure. Generation of hydrogen peroxide in the guard cells, calcium signature and changes in water potential are responsible for the collective stomatal behavior.(4) We further developed an efficient and environmental-friendly antitranspirant with E. coli and Saccharomyces cerevisiae. The application of them to Vicia faba L. and Oryza sativa L. significantly reduced the transpiration and increased the water use efficiency.Our results reveal the delicate interactions between host plants and foliar non-pathogenic microbes. It may be of great significances to the Evolutional ecology, projections of plant diseases and development of environmental-friendly antitranspirant.