MLO Gene Functionality in Powdery Mildew Resistance

The Mildew Locus O (MLO) gene family encodes plant‐specific seven‐transmembrane proteins that serve as susceptibility factors for powdery mildew fungi. Wild‐type MLO proteins act as negative regulators of early defence, facilitating fungal penetration and haustorium formation by modulating cellular processes such as vesicle trafficking, calcium signalling and cell‐wall apposition. Recessive loss‐of‐function alleles (mlo mutations) abolish this susceptibility, triggering rapid formation of papillae, enhanced reactive oxygen species accumulation and deposition of callose at attempted penetration sites. Such mlo‐based resistance has proven durable and broad‐spectrum in barley, wheat and tomato, albeit occasionally accompanied by pleiotropic effects. Phylogenetic analyses have divided MLO homologues into distinct clades, with clade IV predominating in monocots and clade V in dicots, guiding the identification of candidate susceptibility genes across major crops. Advances in genomics and targeted mutagenesis—ranging from TILLING to CRISPR/Cas9—have enabled both the discovery of natural mlo alleles and the generation of customised knockouts. These developments underpin sustainable breeding strategies aimed at reducing reliance on fungicides and improving global food security.

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MLO Gene Functionality in Powdery Mildew Resistance publication trend

The graph below shows the total number of articles in mlo gene functionality in powdery mildew resistance across all publications each year (not limited to Nature Index journals).

Technical terms

MLO gene: A plant gene encoding a seven‐transmembrane protein that, in its wild‐type form, promotes susceptibility to powdery mildew fungi.

mlo resistance: A recessive form of disease resistance arising from loss‐of‐function mutations in MLO genes, leading to enhanced pre-penetration defences.

S-gene (susceptibility gene): A host gene whose normal activity is exploited by a pathogen to establish infection.

CRISPR/Cas9: A programmable genome‐editing system used to induce precise mutations, including gene knockouts, in plants.

Papilla: A localised cell‐wall apposition enriched in callose that forms at sites of attempted fungal ingress, hindering pathogen entry.

Phylogenetic clade: A group of homologous genes sharing a common ancestor, used to predict functional similarity among MLO family members.

References

1. The First Genome-Wide Mildew Locus O Genes Characterization in the Lamiaceae Plant Family. International Journal of Molecular Sciences (2023).
2. Enhancing powdery mildew resistance in soybean by targeted mutation of MLO genes using the CRISPR/Cas9 system. BMC Plant Biology (2023).
3. mlo‐based powdery mildew resistance in hexaploid bread wheat generated by a non‐transgenic TILLING approach. Plant Biotechnology Journal (2016).
4. Loss of Function in Mlo Orthologs Reduces Susceptibility of Pepper and Tomato to Powdery Mildew Disease Caused by Leveillula taurica. PLOS ONE (2013).
5. Topology, Subcellular Localization, and Sequence Diversity of the Mlo Family in Plants*. Journal of Biological Chemistry (1999).