The Loricrin-Like Protein (LLP) of Phytophthora infestans Is Required for Oospore Formation and Plant Infection.

Ting Guo,Wenxian Sun,Xiao-Wen Wang,Li-Yun Guo,Kun Shan

doi:10.3389/fpls.2017.00142

Abstract

Loricrin-like protein (LLP) is characterized by a high content of glycine residues and is a major component of plant cell wall. Here, we identified a Phytophthora infestans ortholog of plant LLP, named PiLLP. In P. infestans, PiLLP is strongly expressed in asexual and sexual developmental stages, including in sporangia, zoospores and germinating cysts, and during oospore formation, as well as in the early stages of infection and during hydrogen peroxide stress. Compared with the wild type, the PiLLP-silenced transformants were defective in oospore formation, had slower colony expansion rates, produced less sporangia with lower germination and zoospore-release rates, and were more sensitive to hydrogen peroxide. Moreover, Nile red staining, and PiLLP-red fluorescent protein fusions indicated that PiLLP is involved in oogonia formation. The silenced transformants also had severely diminished virulence levels that could be partially restored with diphenyleneiodium treatments. The analysis of catalase activity showed a decrease of catalase activity in silenced transformants. Thus, PiLLP is important for sexual and asexual reproduction, and is required for oxidative stress tolerance and plant infection.

Highlights

The oomycetes form a group of fungus-like eukaryotes containing diverse microorganisms that live in saltwater, freshwater, and terrestrial environments (Sparrow, 1960; Karling, 1981)
We identified a gene encoding Loricrin-like protein (LLP) in P. infestans, and designated it as PiLLP
One homolog of PiLLP was found in each oomycete genome, and a phylogenetic analysis showed that all of the oomycete LLPs were grouped into one clade, clustering with the Class V glycine-rich proteins (GRPs) in plants (Figure 1A)

Summary

Introduction

The oomycetes form a group of fungus-like eukaryotes containing diverse microorganisms that live in saltwater, freshwater, and terrestrial environments (Sparrow, 1960; Karling, 1981). Many members of the oomycetes are well-known pathogens of plants and animals, causing severe economic losses. P. infestans reproduces asexually by forming sporangia on sporangiophores. Sporangia in free water germinate directly either via germ tubes at higher temperatures (20– 25◦C), or by releasing zoospores at lower temperatures (10–15◦C) (Ribeiro, 1983). The asexual cycle enables dramatically rapid population growth in susceptible host tissue. Both sporangia and zoospores are important for infection and enable the movement of P. infestans between host plants

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Results

Conclusion