A research team led by Assistant Professor Laurent Zimmerli, Department of Life Science, NTU, discovered two lectin receptor kinases (LecRK-VI.2 and LecRK-V.5) critical for innate immunity in the model plant Arabidopsis thaliana. These findings were recently published in The Plant Cell and PLoS Pathogens journals (IF of respectively 9.396 and 9.079, 2010). It is also the first time for NTU faculties publishing manuscripts in these two journals. These discoveries will pave the way for the production of crops more resistant to microbial pathogens.

Assistant Professor L. Zimmerli is deeply curious about how plant respond to microbial pathogen attacks and has regular publications in high standard journals. His new work demonstrates the importance of a novel class of receptor kinases, the lectin receptor kinases, in plant resistance to microbial pathogens. Although lectin receptor kinase’s role in mammal’s innate immunity is well documented, the function of lectin receptor kinases in plant innate immunity is not clear. The team of Assistant Professor L. Zimmerli uncovered LecRK-VI.2 as a positive regulator of Arabidopsis innate immunity. Notably, lecrk-VI.2-1 knock-out mutants were more sensitive to bacterial infection. Enhanced sensitivity was correlated with reduced innate immunity activation such as defective up-regulation of innate immunity marker genes, impaired callose deposition and stomatal closure upon bacterial infection. Overexpression studies combined with genome-wide microarray analyses indicated that LecRK-VI.2 positively regulates Arabidopsis innate immunity. In addition, the team also pointed out that LecRK-VI.2 works independently of the microbe-associated molecular pattern flagellin receptor complex, suggesting a new signaling pathway in plant innate immunity.

Stomata are small pores on the lower side of leaves that are critical for CO2 uptake and photosynthesis. Pathogenic bacteria penetrate leaf tissue through stomatal openings. As an innate immunity response, plants close stomata that are in contact with bacteria. The team of Assistant Professor L. Zimmerli uncovered LecRK-V.5 as a critical player in Arabidopsis stomatal immunity. Loss of LecRK-V.5 function increased resistance to surface inoculation with virulent bacteria, while lines overexpressing LecRK-V.5 were more susceptible to bacteria. In addition, the team also discovered that LecRK-V.5 is rapidly expressed in stomata after bacterial inoculation. Assistant Professor Zimmerli’s team showed that LecRK-V.5 interfere with abscisic acid signaling, a plant hormone involved in stomatal closure, upstream of reactive oxygen species production. These results provide genetic evidences that LecRK-V.5 negatively regulates stomatal immunity. Zimmerli’s team data reveal that plants have evolved mechanisms to reverse bacteria-mediated stomatal closure to prevent long-term effect on CO2 uptake and photosynthesis.

Climate change, reduced availability of water and land and a rapidly growing human population challenge current agriculture systems to an unforeseen degree. Up to 25 % of agricultural yield is lost every year due to attack by microbial pathogens. Fundamental understanding of how plants respond to and cope with pathogens is thus of utmost importance. The identification of central plant defense elements such as LecRK-VI.2 and LecRK-V.5 may generate novel breeding strategies for establishing a sustainable agricultural system that helps to provide sufficient food for everyone.