The fungal subtilase AsES elicits a PTI‐like defence response in Arabidopsis thaliana plants independently of its enzymatic activity

Abstract

Summary Acremonium strictum elicitor subtilisin (AsES) is a 34‐kDa serine‐protease secreted by the strawberry fungal pathogen A. strictum. On AsES perception, a set of defence reactions is induced, both locally and systemically, in a wide variety of plant species and against pathogens of alternative lifestyles. However, it is not clear whether AsES proteolytic activity is required for triggering a defence response or if the protein itself acts as an elicitor. To investigate the necessity of the protease activity to activate the defence response, AsES coding sequences of the wild‐type gene and a mutant on the active site (S226A) were cloned and expressed in Escherichia coli. Our data show that pretreatment of Arabidopsis plants with inactive proteins, i.e. inhibited with phenylmethylsulphonyl fluoride (PMSF) and mutant, resulted in an increased systemic resistance to Botrytis cinerea and expression of defence‐related genes in a temporal manner that mimics the effect already reported for the native AsES protein. The data presented in this study indicate that the defence‐eliciting property exhibited by AsES is not associated with its proteolytic activity. Moreover, the enhanced expression of some immune marker genes, seedling growth inhibition and the involvement of the co‐receptor BAK1 observed in plants treated with AsES suggests that AsES is being recognized as a pathogen‐associated molecular pattern by a leucine‐rich repeat receptor. The understanding of the mechanism of action of AsES will contribute to the development of new breeding strategies to confer durable resistance in plants.

Identification of Key Residues Essential for the Activation of Plant Immunity by Subtilisin From Bacillus velezensis LJ02

“…Due to the large number of duplications, losses, and functional diversifications in the evolution of subtilisin superfamily, there are large differences in subtilisin phylogeny ( Li et al, 2017 ). Subtilisin has a certain degree of conservation across different classes of microbes to general microbial fitness ( Caro et al, 2020 ), while conserved functional residues are critically important for protein function. For example, specific residues of AtZAR1, a canonical CC-type NLR protein from Arabidopsis , are required for its immune function against Pseudomonas syringae pv.…”

“…tomato DC3000 ( Baudin et al, 2017 ). In search of whether the proteolytic activity of AsES, a subtilisin from Acremonium strictum , is required to trigger the defence response, its mutants at the active site (S226A) have confirmed that AsES induced the plant defense, and that enzymatic and eliciting activities were not associated ( Caro et al, 2020 ). However, key residues of subtilisin triggering defence responses to pathogens remain largely unknown.…”

Molecular and physiological characterization of Arabidopsis–Colletotrichum gloeosporioides pathosystem

“…Arabidopsis thaliana is an important model host for studying plant–pathogen interactions due to the ease with which it can be studied by genetic and mutational analysis. Isolation of pathogens that infect both crops and Arabidopsis has greatly facilitated the understanding of plant defence mechanisms (Caro et al, 2020). Transferring genes involved in innate immunity from model plants to crops could also be a promising alternative for genetic improvement, and several studies have already proved its feasibility (Zhang et al, 2010).…”

“…Arabidopsis thaliana is an important model host for studying plant-pathogen interactions due to the ease with which it can be studied by genetic and mutational analysis. Isolation of pathogens that infect both crops and Arabidopsis has greatly facilitated the understanding of plant defence mechanisms (Caro et al, 2020).…”

The fungal elicitor AsES requires a functional ethylene pathway to activate the innate immunity in strawberry

“…Our research group has identified and characterized a defence elicitor protein called Acremonium strictum Elicitor Subtilisin (AsES), which was isolated from the opportunist fungus Acremonium strictum (Chalfoun et al 2013) (patent AR/10.03.11/ARA P110100854). It was reported that AsES induces a systemic defence response in different strawberry cultivars and in Arabidopsis thaliana by activating a broad spectrum of biochemical and molecular processes associated with the plant defence response (Chalfoun et al 2013; Hael‐Conrad et al 2015; Caro et al 2019). Besides its protective effects in vegetative stages, Perato et al (2018) also reported that AsES induces ripening and enhances protection against naturally produced disease in avocado fruit.…”