Editorial- Molecular tools and mechanisms of rice-Xanthomonas oryzae interactions

Bacterial leaf blight (BLB) and bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), respectively, lead to severe loss in yields and quality in most rice-growing areas around the world. As the staple crop and the model plant for biology research, characterizing the diseases of rice has great significance. It is crucial to elucidate the interaction between the pathogens and rice as well as the mechanisms of pathogenesis and resistance. The special topic of the three papers is the pathogenicity of plant pathogenic bacteria and host resistance to pathogens. Transcription activator-like effectors (TALEs) secreted into plant cell through the type III secretion system (T3SS) are important virulence factors of the pathogens. TALEs’ function depends on the direct interaction between its TFB domain and host plant basal transcription factor IIA gamma subunit (TFIIAγ). The first article from Tian et al. (2019) investigated the key domain and residues of plant TFIIAγ and core residues of TALE TFB domain that are indispensable for TFIIAγ-TALEs interaction in the process of TALE-carrying Xanthomonas invasion plants, which provides theoretical guidance for the subsequent cultivation of disease-resistant rice varieties. The elucidation of molecular mechanism underlying induction of T3SS gene expression is a very important step to lift the veil on global virulence regulation network in Xoo. Thus, in the second paper, Xu et al. (2019) constructed an effective T3SS protein expression vector pH3-flag based on the backbone of almost widely used vector in the pathogens. The experimental results suggested that the expression system will work as a useful molecular tool in understanding some virulence genes expression and regulation in Xoo and other Xanthomonas spp. β-Glucosidase responds to various biotic and abiotic stresses, but its function in disease resistance remains unclear. The third article from Li et al. (2019) mentioned that OsBGLU19 and OsBGLU23, encoding β-glucosidases, mediate rice resistance to BLS. They confirmed that β- glucosidase is involved in the interaction between rice and Xanthomonas. The findings of the papers above highlight our understanding through several novel perspectives, as well as the operational system, on the interaction between plants and pathogenic Xanthomonas for our goals of plant resistance breeding.