Effector Avr4 in Phytophthora infestans Escapes Host Immunity Mainly Through Early Termination.

Abdul Waheed,Yan-Ping Wang,Li-Na Yang,Jiasui Zhan,Zong-Hua Wang,Shi-Ting Liu,Oswald Nkurikiyimfura,Guo-Dong Lu,Wen-Yang Li,Yahuza Lurwanu

doi:10.3389/fmicb.2021.646062

Abstract

Effector genes play critical roles in the antagonistic interactions between plants and pathogens. However, knowledge of mutation mechanisms and evolutionary processes in effector genes and the contribution of climatic factors to the evolution of effector genes are fragmented but important in sustainable management of plant diseases and securing food supply under changing climates. Here, we used a population genetic approach to explore the evolution of the Avr4 gene in Phytophthora infestans, the causal agent of potato blight. We found that the Avr4 gene exhibited a high genetic diversity generated by point mutation and sequence deletion. Frameshifts caused by a single base-pair deletion at the 194th nucleotide position generate two stop codons, truncating almost the entire C-terminal, which is important for effector function and R4 recognition in all sequences. The effector is under natural selection for adaptation supported by comparative analyses of population differentiation (FST) and isolation-by-distance between Avr4 sequences and simple sequence repeat marker loci. Furthermore, we found that local air temperature was positively associated with pairwise FST in the Avr4 sequences. These results suggest that the evolution of the effector gene is influenced by local air temperature, and the C-terminal truncation is one of the main mutation mechanisms in the P. infestans effector gene to circumvent the immune response of potato plants. The implication of these results to agricultural and natural sustainability in future climate conditions is discussed.

Highlights

Plants, with an array of defense machinery, are overwhelmed by a diverse group of pathogens, each deploying with a series of invasive mechanisms (Lamour and Kamoun, 2009; Zhan et al, 2015)
According to our best knowledge, this is the first attempt to understand the population genetic structure, mutation mechanisms, and evolutionary processes of P. infestans Avr4 gene and its interaction with air temperature using a large collection of isolates sampled from various ecological niches
We found a high genetic diversity in the Avr4 gene

Summary

Introduction

With an array of defense machinery (immunity), are overwhelmed by a diverse group of pathogens, each deploying with a series of invasive mechanisms (Lamour and Kamoun, 2009; Zhan et al, 2015). The dynamics of these defense and invasive processes takes place in a co-evolutionary arms race (McDonald and Linde, 2002; Zhan et al, 2014) in which current defense mechanisms in plants select for novel pathogen’s invasive systems that reduce the Evolution of a P. infestans Effector Gene efficacy of existing defenses and trigger the emergence of new defense (Wu et al, 2016) This model of host-pathogen interaction was elucidated more than 70 years ago (Flor, 1942), but its molecular basis has been poorly understood until the 2000s (Jones and Dangl, 2006; Thrall et al, 2016; Yin et al, 2017). The Avr protein secreted by Cladosporium fulvum binds with chitins to protect the pathogen against plant chitinases (Van Der Biezen and Jones, 1998)

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