Project description:Sucrose non-fermenting-1-related protein kinase-1 (SnRK1) belongs to a family of evolutionary conserved kinases with orthologs in all eukaryotes, ranging from yeasts (SnF1) to mammals (AMP-Activated kinase). These kinases sense energy deficits caused by nutrient limitation or stress and coordinate the required adaptations to maintain energy homeostasis and survival. In plants, SnRK1 is a global regulator of plant metabolism and is also involved in abiotic stress responses. Its role in the response to biotic stress, however, is only starting to be uncovered. Here we studied the effect of altered SnRK1a expression on growth and plant defense in rice. OsSnRK1a overexpression interfered with normal growth and development and increased resistance against both (hemi)biotrophic and necrotrophic pathogens, while OsSnRK1a silencing in RNAi lines increased susceptibility. OsSnRK1a overexpression positively affected the salicylic acid pathway and boosted the jasmonate-mediated defense response after inoculation with the blast fungus Pyricularia oryzae. Together these findings strongly suggest OsSnRK1a to be involved in plant basal immunity and favor a model whereby OsSnRK1a acts as a master switch that regulates growth-immunity trade-offs.
Project description:Salicylic acid (SA) is an essential plant hormone that plays critical roles in basal defence and amplification of local immune responses and establishes resistance against various pathogens. However, the comprehensive knowledge of the salicylic acid 5-hydroxylase (S5H) in rice-pathogen interaction is still elusive. Here, we reported that three OsS5H homologues displayed salicylic acid 5-hydroxylase activity, converting SA into 2,5-dihydroxybenzoic acid (2,5-DHBA). OsS5H1, OsS5H2, and OsS5H3 were preferentially expressed in rice leaves at heading stage and responded quickly to exogenous SA treatment. We found that bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) strongly induced the expression of OsS5H1, OsS5H2, and OsS5H3. Rice plants overexpressing OsS5H1, OsS5H2, and OsS5H3 showed significantly decreased SA contents and increased 2,5-DHBA levels, and were more susceptible to bacterial blight and rice blast. A simple single guide RNA (sgRNA) was designed to create oss5h1oss5h2oss5h3 triple mutants through CRISPR/Cas9-mediated gene mutagenesis. The oss5h1oss5h2oss5h3 exhibited stronger resistance to Xoo than single oss5h mutants. And oss5h1oss5h2oss5h3 plants displayed enhanced rice blast resistance. The conferred pathogen resistance in oss5h1oss5h2oss5h3 was attributed to the significantly upregulation of OsWRKY45 and pathogenesis-related (PR) genes. Besides, flg22-induced reactive oxygen species (ROS) burst was enhanced in oss5h1oss5h2oss5h3. Collectively, our study provides a fast and effective approach to generate rice varieties with broad-spectrum disease resistance through OsS5H gene editing.
Project description:Crops carrying broad-spectrum resistance loci provide an effective strategy for controlling infectious disease because these loci typically confer resistance to diverse races of a pathogen or even multiple species of pathogens. Despite their importance, only a few crop broad-spectrum resistance loci have been reported. Here, we report the identification and characterization of the rice bsr-k1 (broad-spectrum resistance Kitaake-1) mutant, which confers broad-spectrum resistance against Magnaporthe oryzae and Xanthomonas oryzae pv oryzae with no major penalty on key agronomic traits. Map-based cloning reveals that Bsr-k1 encodes a tetratricopeptide repeats (TPRs)-containing protein, which binds to mRNAs of multiple OsPAL (OsPAL1-7) genes and promotes their turnover. Loss of function of the Bsr-k1 gene leads to accumulation of OsPAL1-7 mRNAs in the bsr-k1 mutant. Furthermore, overexpression of OsPAL1 in wild-type rice TP309 confers resistance to M. oryzae, supporting the role of OsPAL1 Our discovery of the bsr-k1 allele constitutes a significant conceptual advancement and provides a valuable tool for breeding broad-spectrum resistant rice.
Project description:Rice production is threatened by multiple pathogens. Breeding cultivars with broad-spectrum disease resistance is necessary to maintain and improve crop production. Previously we found that overexpression of miR160a enhanced rice blast disease resistance. However, it is unclear whether miR160a also regulates resistance against other pathogens, and what the downstream signaling pathways are. Here, we demonstrate that miR160a positively regulates broad-spectrum resistance against the causative agents of blast, leaf blight and sheath blight in rice. Mutations of miR160a-targeted Auxin Response Factors result in different alteration of resistance conferred by miR160a. miR160a enhances disease resistance partially by suppressing ARF8, as mutation of ARF8 in MIM160 background partially restores the compromised resistance resulting from MIM160. ARF8 protein binds directly to the promoter and suppresses the expression of WRKY45, which acts as a positive regulator of rice immunity. Mutation of WRKY45 compromises the enhanced blast resistance and bacterial leaf blight resistance conferred by arf8 mutant. Overall, our results reveal that a microRNA coordinates rice broad-spectrum disease resistance by suppressing multiple target genes that play different roles in disease resistance, and uncover a new regulatory pathway mediated by the miR160a-ARF8 module. These findings provide new resources to potentially improve disease resistance for breeding in rice.
Project description:Bacterial blight (BB) induced by Xanthomonas oryzae pv. oryzae (Xoo) is a devastating bacterial disease in rice. The use of disease resistance (R) genes is the most efficient method to control BB. Members of the nucleotide-binding domain and leucine-rich repeat containing protein (NLR) family have significant roles in plant defense. In this study, Xa47, a new bacterial blight R gene encoding a typical NLR, was isolated from G252 rice material, and XA47 was localized in the nucleus and cytoplasm. Among 180 rice materials tested, Xa47 was discovered in certain BB-resistant materials. Compared with the wild-type G252, the knockout mutants of Xa47 was more susceptible to Xoo. By contrast, overexpression of Xa47 in the susceptible rice material JG30 increased BB resistance. The findings indicate that Xa47 positively regulates the Xoo stress response. Consequently, Xa47 may have application potential in the genetic improvement of plant disease resistance. The molecular mechanism of Xa47 regulation merits additional examination.
Project description:Rice blast caused by Magnaporthe oryzae is the most destructive fungal disease in crops, greatly threatening rice production and food security worldwide. The identification and utilization of broad-spectrum resistance genes are considered to be the most economic and effective method to control the disease. In the past decade, many blast resistance ( R) genes have been identified, which mainly encode nucleotide-binding leucine-rich repeat (NLR) receptor family and confer limited race-specific resistance to the fungal pathogen. Resistance genes conferring broad-spectrum blast resistance are still largely lacking. In this study, we carried out a map-based cloning of the new blast R locus Pizh in variety ZH11. A bacterial artificial chromosome (BAC) clone of 165 kb spanning the Pizh locus was sequenced and identified 9 NLR genes, among which only Pizh-1 and Pizh-2 were expressed. Genetic complementation experiments indicated that Pizh-1 but not Pizh-2 alone could confer blast resistance. Intriguingly, both mutations on Pizh-1 and Pizh-2 by CRISPR-Cas9 abolished the Pizh-mediated resistance. We also observed that Pizh-1-mediated resistance was partially dependent on Pizh-2. Pizh-1 and Pizh-2 form a complex of NLRs through direct interaction. This suggests that Pizh-1 may function as the executor NLR and Pizh-2 as a 'helper' NLR that shares functional redundancy with other NLRs. Our current study provides not only a good tool for rice disease resistance breeding but also deep insight into NLR association and function in plant immunity. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.
Project description:Viral pathogens are a major threat to rice production worldwide. Although RNA interference (RNAi) is known to mediate antiviral immunity in plant and animal models, the mechanism of antiviral RNAi in rice and other economically important crops is poorly understood. Here, we report that rice resistance to evolutionarily diverse viruses requires Argonaute18 (AGO18). Genetic studies reveal that the antiviral function of AGO18 depends on its activity to sequester microRNA168 (miR168) to alleviate repression of rice AGO1 essential for antiviral RNAi. Expression of miR168-resistant AGO1a in ago18 background rescues or increases rice antiviral activity. Notably, stable transgenic expression of AGO18 confers broad-spectrum virus resistance in rice. Our findings uncover a novel cooperative antiviral activity of two distinct AGO proteins and suggest a new strategy for the control of viral diseases in rice.
Project description:Rice plants contain high basal levels of salicylic acid (SA), but some of their functions remain elusive. To elucidate the importance of SA homeostasis in rice immunity, we characterized four rice SA hydroxylase genes (OsSAHs) and verified their roles in SA metabolism and disease resistance. Recombinant OsSAH proteins catalyzed SA in vitro, while OsSAH3 protein showed only SA 5-hydroxylase (SA5H) activity, which was remarkably higher than that of other OsSAHs that presented both SA3H and SA5H activities. Amino acid substitutions revealed that three amino acids in the binding pocket affected SAH enzyme activity and/or specificity. Knockout OsSAH2 and OsSAH3 (sahKO) genes conferred enhanced resistance to both hemibiotrophic and necrotrophic pathogens, whereas overexpression of each OsSAH gene increased susceptibility to the pathogens. sahKO mutants showed increased SA and jasmonate levels compared to those of the wild type and OsSAH-overexpressing plants. Analysis of the OsSAH3 promoter indicated that its induction was mainly restricted around Magnaporthe oryzae infection sites. Taken together, our findings indicate that SA plays a vital role in immune signaling. Moreover, fine-tuning SA homeostasis through suppression of SA metabolism is an effective approach in studying broad-spectrum disease resistance in rice.
Project description:Plants are subject to attack by diverse pests and pathogens. Few genes conferring broad-spectrum resistance to both insects and pathogens have been identified. Because of the growth-defense tradeoff, it is often challenging to balance biotic stress resistance and yield for crops. Here, we report that OsWRKY36 suppresses the resistance to insects and pathogens via transcriptional repression of Phenylalanine Ammonia Lyases (PALs), a key enzyme in phenylpropanoid pathway in rice. Knocking out OsWRKY36 causes elevated lignin biosynthesis and increased sclerenchyma thickness of leaf sheath, leading to enhanced resistance to multiple pests and pathogens. Additionally, loss of OsWRKY36 also derepresses the transcription of Ideal Plant Architecture 1 (IPA1) and MONOCULM2 (MOC2), resulting in increased spikelet number per panicle and tiller number. These findings provide mechanistic insights into biotic stress tolerance in rice and offer a promising strategy to breed rice cultivars with broad-spectrum resistance to insects and pathogens while maintaining stable yield.