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SummaryWRKY proteins are transcription factors (TFs) that regulate the expression of defenserelated genes. The salicylic acid (SA)-inducible Oryza sativa WRKY6 (OsWRKY6) was identified as a positive regulator of Oryza sativa pathogenesis-related 10a (OsPR10a) by transient expression assays. A physical interaction between OsWRKY6 and W-box-like element 1 (WLE1), which positively regulates OsPR10a/probenazole induced protein 1 expression, was verified in vitro.Several pathogenesis-related (PR) genes were constitutively activated, including OsPR10a, and transgenic rice (Oryza sativa) plants overexpressing (ox) OsWRKY6 exhibited enhanced disease resistance to pathogens. By contrast, PR gene induction was compromised in transgenic OsWRKY6-RNAi lines, suggesting that OsWRKY6 is a positive regulator of defense responses. OsWRKY6-ox lines displayed leaf lesions, and increased OsWRKY6 levels caused cell death.Salicylic acid (SA) concentrations were higher in OsWRKY6-ox lines than in wild-type (WT) plants, and transcript levels of Oryza sativa isochorismate synthase 1 (OsICS1), which encodes a major enzyme involved in SA biosynthesis, were higher in OsWRKY6-ox lines than in WT. OsWRKY6 directly bound to the OsICS1 promoter in vivo. This indicates that OsWRKY6 can directly regulate OsICS1 expression and thereby increase SA concentrations. OsWRKY6 autoregulates its own expression. OsWRKY6 protein degradation is possibly regulated by ubiquitination.Our results suggest that OsWRKY6 positively regulates defense responses through activation of OsICS1 expression and OsWRKY6 stabilization.

BackgroundPlants are frequently subjected to abiotic and biotic stresses, and WRKY proteins play a pivotal role in the response to such stress. OsWRKY11 is induced by pathogens, drought, and heat, suggesting a function in biotic and abiotic stress responses.ResultsThis study identified OsWRKY11, a member of WRKY group IIc. It is a transcriptional activator that localized to the nucleus. Ectopic expression of OsWRKY11 resulted in enhanced resistance to a bacterial pathogen, Xanthomonas oryzae pv. oryzae; resistance was compromised in transgenic lines under-expressing OsWRKY11. Ectopic expression of OsWRKY11 resulted in constitutive expression of defense-associated genes, whereas knock-down (kd) of OsWRKY11 reduced expression of defense-associated genes during pathogen attack, suggesting that OsWRKY11 activates defense responses. OsWRKY11 bound directly to the promoter of CHITINASE 2, a gene associated with defense, and activated its transcription. In addition, ectopic expression of OsWRKY11 enhanced tolerance to drought stress and induced constitutive expression of drought-responsive genes. Induction of drought-responsive genes was compromised in OsWRKY11-kd plants. OsWRKY11 also bound directly to the promoter of a drought-responsive gene, RAB21, activating its transcription. In addition, OsWRKY11 protein levels were controlled by the ubiquitin-proteasome system.ConclusionOsWRKY11 integrates plant responses to pathogens and abiotic stresses by positively modulating the expression of biotic and abiotic stress-related genes.Electronic supplementary materialThe online version of this article (10.1186/s12284-018-0199-0) contains supplementary material, which is available to authorized users.

OsWRKY51 functions as a positive transcriptional regulator in defense signaling against Xanthomonas oryzae pv. oryzae by direct DNA binding to the promoter of defense related gene, OsPR10a. OsWRKY51 in rice (Oryza sativa L.) is induced by exogenous salicylic acid (SA) and inoculation with Xanthomonas oryzae pv. oryzae (Xoo). To examine the role of OsWRKY51 in the defense response of rice, we generated OsWRKY51 overexpressing and underexpressing transgenic rice plants. OsWRKY51-overexpressing transgenic rice lines were more resistant to Xoo and showed greater expression of defense-related genes than wild-type (WT) plants, while OsWRKY51-underexpressing lines were more susceptible to Xoo and showed less expression of defense-associated genes than WT plants. Transgenic lines overexpressing OsWRKY51 showed growth retardation compared to WT plants. In contrast, transgenic lines underexpressing OsWRKY51 by RNA interference showed similar plant height with WT plants. Transient expression of OsWRKY51-green fluorescent protein fusion protein in rice protoplasts revealed that OsWRKY51 was localized in the nucleus. OsWRKY51 bound to the W-box and WLE1 elements of the OsPR10a promoter. Based on these results, we suggest that OsWRKY51 is a positive transcriptional regulator of defense signaling and has direct DNA binding ability to the promoter of OsPR10a, although it is reported to be a negative regulator in GA signaling.

WRKY proteins play essential roles as negative or positive regulators of pathogen defense. This study explored the roles of different OsWRKY proteins in basal defense and Xa1-mediated resistance to Xanthomonas oryzae pv. oryzae (Xoo) infection in rice. Assays of disease in OsWRKY10KD and OsWRKY88KD lines following infection with an incompatible Xoo race, which induced Xa1-mediated resistance in wild-type plants, showed that OsWRKY10 and OsWRKY88 were positive regulators of Xa1-mediated resistance. OsWRKY10 also acted as a positive regulator in basal defense by directly or indirectly activating transcription of defense-related genes. OsWRKY10 activated the OsPR1a promoter by binding to specific WRKY binding sites. Two transcriptional regulatory cascades of OsWRKY10 were identified in basal defense and Xa1-mediated resistance. In the first transcriptional regulatory cascade, OsWRKY47 acted downstream of OsWRKY10 whereas OsWRKY51 acted upstream. OsWRKY10 activated OsPR1a in two distinct ways: by binding to its promoter and, at the same time, by indirect activation through OsWRKY47. In the second transcriptional regulatory cascade, OsWRKY47 acted downstream of OsWRKY10, and OsWRKY88 acted upstream. These OsWRKY10 transcriptional regulatory cascades played important roles in basal defense and Xa1-mediated resistance to enable the mounting of a rapid immune response against pathogens.

Pectobacterium carotovorum subsp. carotovorum causes soft rot disease in various plants, including Chinese cabbage. The simple extracellular leucine-rich repeat (eLRR) domain proteins have been implicated in disease resistance. Rice leucine-rich repeat protein (OsLRP), a rice simple eLRR domain protein, is induced by pathogens, phytohormones, and salt. To see whether OsLRP enhances disease resistance to bacterial soft rot, OsLRP was introduced into Chinese cabbage by Agrobacterium-mediated transformation. Two independent transgenic lines over-expressing OsLRP were generated and further analyzed. Transgenic lines over-expressing OsLRP showed enhanced disease resistance to bacterial soft rot compared to non-transgenic control. Bacterial growth was retarded in transgenic lines over-expressing OsLRP compared to non-transgenic controls. We propose that OsLRP confers enhanced resistance to bacterial soft rot. Monitoring expression of defense-associated genes in transgenic lines over-expressing OsLRP, two different glucanases and Brassica rapa polygalacturonase inhibiting protein 2, PDF1 were constitutively activated in transgenic lines compared to non-transgenic control. Taken together, heterologous expression of OsLRP results in the activation of defense response and enhanced resistance to bacterial soft rot.

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Barley and wheat are a major food crop of humans, along with rice, soybean and corn. A systematic breeding program for Korean barley began in 1906 with selection and introduction breeding. In 1908, landrace barley was collected, and breeding focused on selection and introduction for high yielding varieties until the 1970s. In the 1980s and 1990s, breeding was carried out for diversity; thereafter, we aimed to improve quality, productivity and lodging tolerance that can be applied to the paddy field in Korea. Since 2010, the major result of breeding was shortening cultivation to approximately 6-12 days, making a double cropping system possible in the paddy field in Korea. Yield has increased by 1.2 times from 438 kg/10 a in the 1960s to 536 kg/10 a in the 2010s, and farm yield has increased by 1.7 times. In addition, as cultivation safety has been enhanced, the varieties have also improved, such as the covered barley used in making tea and other processing products. In case of wheat, up to now forty cultivars have been developed in Korea. In the early stage, we developed a domestic wheat variety that was early maturing and high yielding. As a result, the maturation time of wheat planted in the 1970s to 2010 was shortened (from 13 to 30 days), while productivity increased by 30% from 408 kg/10 a in the 1970s to 532 kg/10 a in 2010. In recent years, there have been remarkable efforts for a more stable production by focusing on increasing disaster and pest resistance due to climate change. In addition, a wheat variety discrimination marker was developed using a variety-specific marker, and selection was made using a trait-specific marker at the early stage of breeding to enhance breeding efficiency. In the 2000s, winter cereals for forage have been promoted to expand forage production and to replace imported feed grains. Therefore, winter cereal that is useful for feed, such as rye, oat, and triticale, have had various varieties and safe production techniques developed. Currently, our research goal for winter cereals for feed is to develop a double-cropping adaptation and abiotic stress tolerance cultivar, and safe production in paddy field. Hence, aggressive action is needed to support the strategic survival of the Korean wheat and barley industry. Barley is a health food that requires a multifaceted effort to improve breeding efficiency, develop varieties that contain large amounts of functional components and are more resistant to stronger biotic and abiotic stresses in response to climate change. It is necessary to recognize the role of wheat and barley as the second main crop after rice, and to improve the self-sufficiency rate of these crops for the health and food industry crisis of Korea.