Structural and Functional Analysis of the Lectin-like Protein Llp1 Secreted by Ustilago maydis upon Infection of Maize

TL;DR

This paper investigates a lectin-like protein secreted by a fungus that infects maize, exploring its structure and potential role in the infection process.

Contribution

The study identifies and characterizes a new lectin-like protein, Llp1, and suggests it belongs to a family of functionally redundant proteins in Ustilago maydis.

Findings

Llp1 is a secreted lectin-like protein with a sugar-binding potential, as observed on the fungal cell wall.

Deletion of llp1 does not affect fungal virulence, indicating functional redundancy with other lectin-like proteins.

Structural analysis reveals multiple lectin-like proteins in U. maydis that may compensate for Llp1's absence.

Abstract

The biotrophic fungus Ustilago maydis, which causes smut disease in maize, secretes numerous proteins upon plant colonization. Some of them, termed effectors, help to evade plant defenses and manipulate cellular processes within the host. The function of many proteins specifically secreted during infection remains elusive. In this study, we biochemically characterized one such protein, UMAG_00027, that is highly expressed during plant infection. We show that UMAG_00027 is a secreted protein with a lectin-like fold and therefore term it Llp1 (lectin-like-protein 1). Llp1 decorated the fungal cell wall of cells grown in axenic culture or proliferating in planta, which is in agreement with its potential sugar-binding ability. We were unable to identify the precise sugar moieties that are bound by Llp1. CRISPR/Cas9-mediated deletion of llp1 reveals that the gene is not essential for fungal virulence. A structural search shows the presence of several other lectin-like proteins in U. maydis that might compensate for the function of Llp1 in ∆llp1 mutants. We therefore speculate that Llp1 is part of a family of lectin-like proteins with redundant functions.

Figures