Potential Role of Laccases in the Relationship of the Maize Late Wilt Causal Agent, Magnaporthiopsis maydis, and Its Host.

Ofir Degani,Yuval Goldblat

doi:10.3390/jof6020063

Abstract

Late wilt is a vascular disease of maize (Zea mays L.) caused by the soil-borne and seed-borne fungus Magnaporthiopsis maydis. The pathogen penetrates the roots of maize plants at the seedling stage, grows into the xylem vessels, and gradually spreads upwards. From the flowering stage to the kernel ripening, the fungal hyphae and secreted materials block the water supply in susceptible maize cultivars, leading to rapid dehydration and death. Laccase is an enzyme secreted by fungus for diverse purposes. The M. maydis laccase gene was identified in our laboratory, but under what conditions it is expressed and to what functions remain unknown. In the current study, we tested the influence of plant age and tissue source (roots or leaves) on M. maydis laccase secretion. The results show increasing laccase secretion as corn parts (as ground tissue) were added to the minimal medium (MM). Furthermore, roots stimulated laccase secretion more than leaves, and adult plants enhanced laccase secretion more than young plants. This implies the possibility that the richer lignin tissue of adult plants may cause increased secretion of the enzyme. In vitro pathogenicity assay proved the ability of M. maydis to develop inside detached roots of maize, barley, watermelon, and cotton but not peanut. Testing root powder from those plants in MM revealed a negative correlation between M. maydis growth (expressed as biomass) and laccase secretion. For example, while the addition of maize, barley, or cotton root powder led to increasing fungal dry weight, it also resulted in relatively lower laccase activity. Watermelon and peanut root powder led to opposite responses. These findings suggest a pivotal role of laccase in the ability of M. maydis to exploit and grow on different host tissues. The results encourage further examination and a deeper understanding of the laccase role in these interesting host–pathogen interactions.

Highlights

The maize late wilt disease causes severe damage to cornfields throughout Israel
M. maydis can survive in the soil or by developing inside an alternative host plant, such as Lupinus termis L. [5], Gossypium hirsutum L., Citrullus lanatus, and Setaria viridis [6,7]
All fungal colonies were grown on solid potato dextrose agar (PDA) medium (Difco, Detroit, MI, USA) at 28 ± 1 ◦ C in the dark for 4–6 days

Summary

Introduction

The maize late wilt disease causes severe damage to cornfields throughout Israel. The disease is characterized by rapid wilt of sweet and fodder maize, mainly from the tasseling stage phase until shortly before maturity [1]. The causal agent of the disease is the phytopathogenic fungus. Magnaporthiopsis maydis (synonyms are Harpophora maydis and Cephalosporium maydis) [2]. The pathogen is a hemibiotroph, soil-borne [3], and seed-borne [4] fungus transmitted as spores, sclerotia, or hype on plant residues. M. maydis can survive in the soil (for long periods) or by developing inside an alternative host plant, such as Lupinus termis L. (lupine) [5], Gossypium hirsutum L. (cotton), Citrullus lanatus (watermelon), and Setaria viridis (green foxtail) [6,7].

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Conclusion