A fungal effector and a rice NLR protein have antagonistic effects on a Bowman-Birk trypsin inhibitor.

Chongyang Zhang,Maria Bellizzi,Xueping Zhou,Jiyang Wang,Jiangbo Fan,Guo‐Liang Wang,Pengfei Bai,Feng He,Yuese Ning,Hong Fang,Xuetao Shi,Ruyi Wang,Chan‐Ho Park

doi:10.1111/pbi.13400

Abstract

SummaryBowman–Birk trypsin inhibitors (BBIs) play important roles in animal and plant immunity, but how these protease inhibitors are involved in the immune system remains unclear. Here, we show that the rice (Oryza sativa) BBI protein APIP4 is a common target of a fungal effector and an NLR receptor for innate immunity. APIP4 exhibited trypsin inhibitor activity in vitro and in vivo. Knockout of APIP4 in rice enhanced susceptibility, and overexpression of APIP4 increased resistance to the fungal pathogen Magnaporthe oryzae. The M. oryzae effector AvrPiz‐t interacted with APIP4 and suppressed APIP4 trypsin inhibitor activity. By contrast, the rice NLR protein Piz‐t interacted with APIP4, enhancing APIP4 transcript and protein levels, and protease inhibitor activity. Our findings reveal a novel host defence mechanism in which a host protease inhibitor targeted by a fungal pathogen is protected by an NLR receptor.

Highlights

BBIs from plants such as wheat (Triticum aestivum) and maize can strongly inhibit the growth of plant pathogenic fungi (Chen et al, 1999; Chilosi et al, 2000). These results suggest that the BBIs play an important role in animal and plant immunity
We report that the M. oryzae effector AvrPiz-t targets and inhibits the activity of the rice BBI APIP4 (AvrPiz-t Interacting Protein 4) to facilitate infection
The protease from M. oryzae that targets APIP4, how AvrPiz-t affects APIP4 trypsin inhibitor activity and whether the trypsin inhibitor activity of APIP4 is involved in rice immunity are still unclear, our study suggests that M. oryzae effectors can target host protease inhibitors in the intracellular space

Summary

Introduction

Phytopathogens have evolved multiple strategies to attack plants, including the secretion of effector proteins into host cells During their coevolution with pathogens, plants have developed receptors and other proteins that recognize pathogen factors to trigger immune responses (Jones and Dangl, 2006; Jones et al, 2016). The Ustilago maydis effector protein Pit inhibits a set of maize (Zea mays) cysteine proteases to undermine host resistance (Mueller et al, 2013) These studies indicate that the suppression of host proteases by pathogen inhibitors is a common strategy to subvert host immunity. To protect PsXEG1 from inhibition by GmGIP1 in the apoplast, P. sojae secretes PsXLP1, a paralog of PsXEG1 (Ma et al, 2016) It is unknown whether the cytoplasmic effectors from pathogens target host protease inhibitors to subvert immunity

Results

Discussion

Conclusion