Ankyrin (ANK) repeat domain-containing proteins comprise one of the largest known protein superfamilies in all species including plants. Recently, several genomeanalysis studies have provided valuable information on the structure of ANK proteins in plants. Among the 13 subgroups based on the presence of various additional domains in addition to the ANK domain, the E3 ubiquitin ligase activity and transcriptional regulation functions of ANK-RF and ANK-ZF subgroup members, respectively, are relatively well understood. NPR1 (nonexpressor of pathogenesis-related1), a key regulator of systemic acquired resistance in Arabidopsis, is a noteworthy member of the ANK-BTB subgroup; however, ANK-M and ANK-TM, the two main subgroups, have been less functionally characterized. With the ability to mediate protein-protein interactions, the majority of plant ANK proteins play crucial roles in defense responses and, on occasion, functions in growth and development. In this review, we summarize on the current knowledge of plant ANK superfamily members and focus on ANK proteins involved in defense responses. In addition, we provide a valuable framework for the future functional characterization of ANK genes with current unknown function in rice, a model crop species.
WRKY proteins play important roles in transcriptional reprogramming in plants in response to various stresses including pathogen attack. In this study, we functionally characterized a rice WRKY gene, OsWRKY67, whose expression is upregulated against pathogen challenges. Activation of OsWRKY67 by T-DNA tagging significantly improved the resistance against two rice pathogens, Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae (Xoo). Reactive oxygen species (ROS) rapidly accumulated in OsWRKY67 activation mutant lines in response to elicitor treatment, compared with the controls. Overexpression of OsWRKY67 in rice confirmed enhanced disease resistance, but led to a restriction of plant growth in transgenic lines with high levels of OsWRKY67 protein. OsWRKY67 RNAi lines significantly reduced resistance to M. oryzae and Xoo isolates tested, and abolished XA21-mediated resistance, implying the possibility of broad-spectrum resistance from OsWRKY67. Transcriptional activity and subcellular localization assays indicated that OsWRKY67 is present in the nucleus where it functions as a transcriptional activator. Quantitative PCR revealed that the pathogenesis-related genes, PR1a, PR1b, PR4, PR10a, and PR10b, are upregulated in OsWRKY67 overexpression lines. Therefore, these results suggest that OsWRKY67 positively regulates basal and XA21-mediated resistance, and is a promising candidate for genetic improvement of disease resistance in rice.
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