The study of rice innate immunity with visual biotechnology
Letian Chen1^*, Fengpin Wang¹, Xiaoyu Wang¹, Yaoguang Liu¹, Ko Shimamoto²

¹State key laboratory for conservation and utilization of subtropical agro-bioresources, college of Life Sciences, South China Agricultural University, Guangzhou 510642, P. R. China.
²Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.
*Correspondence: lotichen@scau.edu.cn

Abstract
Visual biotechnology based on laser microscopy and fluorescent proteins becomes the state-of-the-art approach to study molecular mechanism in vivo. Rice and blast fungus are ideal model organisms to understand the plant-microbe interaction. Using FRET sensor, we demonstrated that chitin, a major PAMP signal for rice innate immunity, was able to activate molecular switch OsRac1 in minutes. We also found that a novel OsRac1 interactor, Hop/Sti1a was associated with chitin receptor OsCERK1 in vivo and important for chitin-triggered immune responses and rice blast resistance. We further revealed that Hop/Sti1 regulated the maturation and transport of OsCERK1 in the endoplasmic reticulum (ER) in a complex with Hsp90. Subsequently, the mature OsCERK1 was transported via the trafficking system to the plasma membrane (PM) for signal perception. Impairment of Hop/Sti1 and Hsp90 function reduces the efficiency of OsCERK1 transport to the PM leading to a defect of in chitin-triggered defense and fungal resistance. On the other hand, Pi-ta/AVR-Pita is a classic pathosystem to study effector-triggered immunity in rice. We demonstrated that Pi-ta was colocalized with AVR-Pita in the mitochondria and interacted with a mitochondrial protein COX11. Therefore, the visual biotechnologies provide insightful information on the signal transduction of rice innate immunity.

Key Words: Innate Immunity; Small GTPase; Chitin; CERK1; Pi-ta; AVR-Pita