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In animals, malectin is well known to play an essential role in endoplasmic reticulum quality control (ERQC) by interacting with ribophorin I, one unit of the oligosaccharyltransferase (OST) complex. However, the functions of malectin in plants remain largely unknown. Here, we demonstrate the rice OsMLD1 is an ER- and Golgi-associated malectin protein and physically interacts with rice homolog of ribophorin I (OsRpn1), and its disruption leads to spontaneous lesion mimic lesions, enhanced disease resistance, and prolonged ER stress. In addition, there are many more N-glycosites and N-glycoproteins identified from the mld1 mutant than wildtype. Furthermore, OsSERK1 and OsSERK2, which have more N-glycosites in mld1, were demonstrated to interact with OsMLD1. OsMLD1 can suppress OsSERK1- or OsSERK2-induced cell death. Thus, OsMLD1 may play a similar role to its mammalian homologs in glycoprotein quality control, thereby regulating cell death and immunity of rice, which uncovers the function of malectin in plants. [ABSTRACT FROM AUTHOR]

Summary: Lesion mimic mutants are used to elucidate mechanisms controlling plant responses to pathogen attacks and environmental stresses. Although dozens of genes had been functionally demonstrated to be involved in lesion mimic phenotype in several plant species, the molecular mechanisms underlying the hypersensitive response are largely unknown. Here, a rice (Oryza sativa) lesion mimic mutant natural blight leaf 3 (nbl3) was identified from T‐DNA insertion lines. The causative gene, OsNBL3, encodes a mitochondrion‐localized pentatricopeptide repeat (PPR) protein. The nbl3 mutant exhibited spontaneous cell death response and H2O2 accumulation, and displayed enhanced resistance to the fungal and bacterial pathogens Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae. This resistance was consistent with the up‐regulation of several defence‐related genes; thus, defence responses were induced in nbl3. RNA interference lines of OsNBL3 exhibited enhanced disease resistance similar to that of nbl3, while the disease resistance in overexpression lines did not differ from that of the wild type. In addition, nbl3 displayed improved tolerance to salt, accompanied by up‐regulation of several salt‐associated marker genes. OsNBL3 was found to mainly participate in the splicing of mitochondrial gene nad5 intron 4. Disruption of OsNBL3 leads to the reduction in complex I activity, the elevation of alternative respiratory pathways and the destruction of mitochondrial morphology. Overall, the results demonstrated that the PPR protein‐coding gene OsNBL3 is essential for mitochondrial development and functions, and its disruption causes the lesion mimic phenotype and enhances disease resistance and tolerance to salt in rice. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]