Investigating the adhesion of encysted zoospores of the oomycete Phytophthora cinnamomi during the early infection of avocado

Abstract

Phytophthora cinnamomi utilizes motile zoospores that chemotactically move towards a potential host to initiate infection. The release of adhesive material from encysting zoospores in P. cinnamomi confers a biological advantage to this pathogen and allows it to successfully attach. There is limited information on Phytophthora adhesion genes. In this study, putative adhesion genes were identified in the recently available P. cinnamomi GKB4 genome, these included six adhesins, five CBELs, and 23 Mucinlike proteins. Several adhesins, CBELs, and mucins were upregulated as early as 6 hours post inoculation (hpi) and late (120 hpi), indicating a role in the biotrophic and necrotrophic phases of infection. The adhesion of P. cinnamomi encysted zoospores on susceptible avocado (Ettinger) roots was examined through the use of scanning electron microscopy (SEM). SEM results showed that P. cinnamomi cysts can attach to the roots of avocado as early as 1 hpi and germinate predominantly at 3 and 6 hpi. Adhesive material was observed on the surface of cysts and germinating cysts. The expression profiles of three adhesion genes coding for adhesin-like (U6809), cellulose binding elicitor lectin (CBEL) (U6169), and mucin-like (U8949) proteins during avocado infection were generated from different stages of infection of Ettinger plants using quantitative Reverse Transcriptase PCR (qRT-PCR). The mucin gene was shown to be significantly upregulated at 3 and 6 hpi, indicating the potential role of this mucin in the early stages of avocado infection. P. cinnamomi appears to employ different adhesion genes during the different stages of avocado infection. This study provides a framework for further research aimed at understanding the role of adhesion in the P. cinnamomi-avocado interaction