The major disease resistance gene Xa4 confers race-specific durable resistance against Xanthomonas oryzae pv. oryzae, which causes the most damaging bacterial disease in rice worldwide. Although Xa4 has been one of the most widely exploited resistance genes in rice production worldwide, its molecular nature remains unknown. Here we show that Xa4, encoding a cell wall-associated kinase, improves multiple traits of agronomic importance without compromising grain yield by strengthening the cell wall via promoting cellulose synthesis and suppressing cell wall loosening. Strengthening of the cell wall by Xa4 enhances resistance to bacterial infection, and also increases mechanical strength of the culm with slightly reduced plant height, which may improve lodging resistance of the rice plant. The simultaneous improvement of multiple agronomic traits conferred by Xa4 may account for its widespread and lasting utilization in rice breeding programmes globally.

SummaryOutbreaks of spring viraemia of carp virus (SVCV) in several carp species and other cultivated fish can cause significant mortality and jeopardize the billion-dollar worldwide fish industry. Spring viraemia of carp virus, also known as Rhabdovirus carpio, is a bullet-shaped RNA virus that enters and amplifies in gill epithelium and later spreads to internal organs. Young fish under stressed conditions (spring cold water, etc.) are more vulnerable to SVCV-induced lethality because of their lack of a mature immune system. Currently, the host response of SVCV remains largely unknown. Here, we observed that autophagy is activated in SVCVinfected epithelioma papulosum cyprini (EPC) cells. We demonstrated that the SVCV glycoprotein, rather than viral replication, activates the autophagy pathway. In addition, SVCV utilized the autophagy pathway to facilitate its own genomic RNA replication and to enhance its titres in the supernatants. Autophagy promoted the survival of SVCV-infected cells by eliminating damaged mitochondrial DNA generated during viral infection. We further showed that SVCV induces autophagy in EPC cells through the ERK/mTOR signalling pathway. Our results reveal a connection between autophagy and SVCV replication and propose autophagy suppression as a novel means to restrict SVCV viral replication.

Dear Editor, Mitochondria are essential organelles in cellular metabolism, homeostasis, and apoptosis. 1,2 Most mitochondrial proteins are synthesized as precursors in the cytosol and then imported into mitochondria by specific protein translocase complexes, including the translocase of the outer membrane complex (TOM complex), the carrier translocase of the inner membrane complex (TIM22 complex), the presequence translocase of the inner membrane complex (TIM23 complex), the sorting and assembly machinery (SAM complex), and the mitochondrial import complex (MIM complex). 3 The TIM22 complex is responsible for the translocation and insertion of hydrophobic membrane proteins, including mitochondrial carrier proteins and translocase subunits (Tim17, Tim22 and Tim23). 3 In humans, TIM22 is a 440-kDa complex comprising at least six components: the hypothetical channelforming protein Tim22, three small Tim proteins (Tim9, Tim10a and Tim10b), Tim29 and acylglycerol kinase (AGK). 1 Considering the functional importance of mitochondrial protein import, the TIM22 complex has been linked to many diseases. For example, mutations in the TIM22 gene have been reported to cause earlyonset mitochondrial myopathy. 4 AGK participates in lipid biosynthesis, and mutations in the AGK gene lead to Sengers syndrome. 2 Mutations in the TIMM8A gene (also called DDP1) cause deafness dystonia syndrome. 2 Despite advances in our knowledge of the function and pathophysiology of the TIM22 complex, reports of its structural characterization are scarce. The structural studies of the TIM22 complex are restricted to the investigation of the structures of Tim9/10a 5,6 and Tim9/10/12 hexameric chaperone 7 and a nuclear magnetic resonance (NMR) analysis of carrier precursors associated with the Tim9/Tim10 complex. 8 Here, we report the cryo-EM structure of the human TIM22 complex at an overall resolution of 3.7 Å. We coexpressed all six known components of the TIM22 complex in human embryonic kidney (HEK) 293 F cells (Fig. 1a). After Flag tag affinity purification followed by gel filtration, the resultant TIM22 complex displayed good resolution behavior (Fig. 1b). The apparent molecular weight was assessed by blue native PAGE to be approximate 440 kDa (Supplementary information, Fig. S1a), consistent with previous findings. 9-12 Mass spectrometry (MS) analysis of the purified complex confirmed the presence of all known components of the TIM22 complex. Furthermore, mitochondria from cells overexpressing the TIM22 complex exhibited more efficient carrier-importing activity than those from wild-type cells (Supplementary information,

Plant cell walls are the first physical barrier against pathogen invasion, and plants thicken the cell wall to strengthen it and restrain pathogen infection. Bacterial blight is a devastating rice (Oryza sativa) disease caused by Xanthomonas oryzae pv. oryzae (Xoo), which typically enters the rice leaf through hydathodes and spreads throughout the plant via the xylem. Xoo interacts with cells surrounding the xylem vessel of a vascular bundle, but whether rice strengthens the sclerenchyma cell walls to stop pathogen proliferation is unclear. Here, we found that a WRKY protein, OsWRKY53, negatively confers resistance to Xoo by strengthening the sclerenchyma cell walls of the vascular bundle. OsMYB63 acts as a transcriptional activator and promotes the expression of three secondary cell wall-related cellulose synthase genes to boost cellulose accumulation, resulting in thickened sclerenchyma cell walls. Both OsWRKY53 and OsMYB63 are abundantly expressed in sclerenchyma cells of leaf vascular bundles. OsWRKY53 functions as a transcriptional repressor and acts genetically upstream of OsMYB63 to suppress its expression. The OsWRKY53-overexpressing and OsMYB63 knockout plants had thinner sclerenchyma cell walls, showing susceptibility to Xoo, while the OsWRKY53 knockout and OsMYB63-overexpressing plants had thicker sclerenchyma cell walls, exhibiting resistance to Xoo. These results suggest that modifying these candidate genes provides a strategy to improve rice resistance to bacterial pathogens.

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Barrels that build barrels Cells produce specialized machinery to produce functional β-barrel proteins that are involved in cross-membrane transport and membrane protein biogenesis in eukaryotic organelles and some bacteria. Wang et al . studied one of these systems that is itself a β-barrel, the mitochondrial sorting and assembly machinery (SAM), in complex with one of its client proteins, translocase of the outer membrane (TOM). TOM subunits can be added one at a time while the protein is bound to SAM. Compared with the full TOM core complex, the final TOM core subunit clashes with SAM and suggests that release of TOM may be driven by its association. —MAF

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