Transcription activator-like (TAL) effectors are major virulence factors secreted by the type III secretion systems of Xanthomonas oryzae pv. oryzicola (Xoc) and X. oryzae pv. oryzae (Xoo), causing bacterial leaf streak and bacterial blight, respectively, in rice. However, the knowledge of Xoc TAL effector function in promoting bacterial virulence remains limited.Here, we isolated the highly virulent Xoc strain HGA4 from the outbreak region of Huanggang (Hubei, China), which contains four TAL effectors not found in the Chinese model strain RS105. Among these, Tal2b was selected for introduction into RS105, which resulted in a longer lesion length than that in the control.Tal2b directly binds to the promoter region of the gene and activates the expression of OsF3H 03g , which encodes 2-oxoglutarate-dependent dioxygenase in rice. OsF3H 03g negatively regulates salicylic acid (SA)-related defense by directly reducing SA, and it plays a positive role in susceptibility to both Xoc and Xoo in rice.OsF3H 03g interacts with a uridine diphosphate-glycosyltransferase protein (OsUGT74H4), which positively regulates bacterial leaf streak susceptibility and may inactivate SA via glycosylation modification.

Phytopathogens and pests are two major factors that limit the growth of plants. The expression of a flavonoid regulator gene, AtMYB12(AT2G47460), has been reported to increase the endogenous flavonoid content of tobacco and tomato. Previous research has only focused on the regulation mechanism of v-myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors under single stress conditions. Here, research showed that AtMYB12 was involved in regulating the resistance of tobacco to multiple biological stresses such as phytopathogens and aphid. We reported that transgenic tobacco carrying AtMYB12 was more resistant to Ralstonia solanacearum when the up-regulated expression of several defense-related markers, such as NbPR1a, NbNOA1, and NbrbohB, was activated, suggesting that the priming defense of a plant may contribute to bacterial disease resistance. The improvement of the resistance of AtMYB12-expressing transgenic tobacco is achieved by promoting the production of ROS, H2O2, and NO. AtMYB12-expressing transgenic tobacco also has resistance to fungal pathogens, such as Colletotrichum nicotianae Averna and Alternaria alternate. The enrichment of flavonols components, such as rutin, which directly inhibit the growth of C. nicotianae and A. alternate, may also contribute to the defense mediated by AtMYB12 over-expression. At the same time, the results also confirm that AtMYB12-expressing transgenic tobacco enhanced plant resistance to aphid-infested (Aphidoidea) pests. These results suggest that the AtMYB12 gene is a good candidate for pest and disease control, with limited resistance costs and enrichment in flavonols, and that AtMYB12 has a potential in the breeding of disease-resistant tobacco crops.

Xanthomonas oryzae delivers transcription activator-like effectors (TALEs) into plant cells to facilitate infection. Following economic principles, the redundant TALEs are rarely identified in Xanthomonas. Previously, we identified the Tal2b, which activates the expression of the rice 2-oxoglutarate-dependent dioxygenase gene OsF3H03g to promote infection in the highly virulent strain of X. oryzae pv. oryzicola HGA4. Here, we reveal that another clustered TALE, Tal2c, also functioned as a virulence factor to target rice OsF3H04g, a homologue of OsF3H03g. Transferring Tal2c into RS105 induced expression of OsF3H04g to coincide with increased susceptibility in rice. Overexpressing OsF3H04g caused higher susceptibility and less salicylic acid (SA) production compared to wild-type plants. Moreover, CRISPR–Cas9 system-mediated editing of the effector-binding element in the promoters of OsF3H03g or OsF3H04g was found to specifically enhance resistance to Tal2b- or Tal2c-transferring strains, but had no effect on resistance to either RS105 or HGA4. Furthermore, transcriptome analysis revealed that several reported SA-related and defense-related genes commonly altered expression in OsF3H04g overexpression line compared with those identified in OsF3H03g overexpression line. Overall, our results reveal a functional redundancy mechanism of pathogenic virulence in Xoc in which tandem Tal2b and Tal2c specifically target homologues of host genes to interfere with rice immunity by reducing SA.