GLOX3 is involved in pollen tube growth and potentially mediates self-incompatibility in Citrus

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Dear Editor, Self-incompatibility (SI) in Citrus is a crucial mechanism controlling reproductive success and hybrid formation, yet the molecular components that act beyond the canonical S-locus remain poorly understood (Liang et al. 2020; Cai et al. 2024; Hu et al. 2024, 2025). In this study, we used the mature peptide regions of S1-, S2-, S5-, and S6-RNases as bait in yeast 2-hybrid screens and identified several putative interacting genes that encode putative S-RNase binding proteins. Among them, Cg1g012490, which is annotated as a glyoxal oxidase gene (CgGLOX3) in the Citrus grandis (L.) Osbeck cv. “Wanbaiyou” v1.0 genome, was identified. This potential non-S factor was involved in the gametophytic SI (GSI) system of pummelo (C. grandis). Glyoxal oxidase (GLOX) is a type of copper-containing radical oxidase that is widely distributed amongst fungi, plants, and microorganisms. Its primary function is to catalyze the oxidation of aldehyde compounds, such as glyoxal and methylglyoxal (MG), into their corresponding carboxylic acids, accompanied by the generation of hydrogen peroxide (H2O2) (Daou and Faulds 2017). A role for CgGLOX3 in citrus SI has not yet been investigated.