Tar Spot of Maize: Current knowledge of genetic interactions and future research prospects to improve disease resistance

Abstract

The emergence and spread of crop plant pathogens pose a significant risk to global food and nutritional security. Of particular concern are those fungal pathogens that can significantly reduce yields of staple crop plants such as maize (Zea mays subsp. mays ). One such plant pathogen is Phyllachora maydis Maubl (P. maydis ), which causes tar spot disease on maize. Though it was only recently identified within the United States, P. maydis is now considered one of the most economically important foliar diseases of maize and has since spread to most maize production areas within the United States and Canada, resulting in substantial yield losses. In this mini-review, we aim to summarize recent advancements in our understanding of the genetic interactions between maize and P. maydis whilst also highlighting future research prospects for developing genetic-based resistances.

Candidate effector proteins from the maize tar spot pathogenPhyllachora maydislocalize to diverse plant cell compartments

“…Recent sequencing of the Phyllachora maydis genome revealed that this fungal pathogen encodes putatively secreted effector candidate proteins (Telenko et al, 2020). However, our general understanding of host cell compartments targeted by the P. maydis effector repertoire is limited (Helm et al, 2022). In this study, we leveraged the availability of the P. maydis genome and refined previous effector predictions to investigate the subcellular compartments targeted by candidate effector proteins using a Nicotiana benthamiana -based heterologous expression system (Figure 1).…”

“…Analysis of the P. maydis genome revealed 462 proteins comprising the predicted secretome, of which 59 contain effector-like sequence characteristics as predicted by EffectorP (v2.0) (Telenko et al, 2020). To date, our understanding of how P. maydis utilizes its effector repertoire to promote virulence as well as the subcellular compartments targeted by these putative effectors remains limited even though this fungal pathogen represents a serious economic concern for maize growers (Helm et al, 2022; Mueller et al, 2020; Valle-Torres et al, 2020). The inability to culture or genetically manipulate P. maydis (Rocco da Silva et al, 2021; Valle-Torres et al, 2020) substantially hinders investigations aimed at characterizing its effector repertoire (Helm et al, 2022).…”

“…To date, our understanding of how P. maydis utilizes its effector repertoire to promote virulence as well as the subcellular compartments targeted by these putative effectors remains limited even though this fungal pathogen represents a serious economic concern for maize growers (Helm et al, 2022; Mueller et al, 2020; Valle-Torres et al, 2020). The inability to culture or genetically manipulate P. maydis (Rocco da Silva et al, 2021; Valle-Torres et al, 2020) substantially hinders investigations aimed at characterizing its effector repertoire (Helm et al, 2022). To circumvent these limitations, the field of effector biology utilizes a surrogate plant system to express epitope-tagged candidate effectors directly inside leaf cells using Agrobacterium -mediated infiltration (agroinfiltration) (Lorrain et al, 2018).…”