Diterpenoids are the major group of antimicrobial phytoalexins in rice 1,2 . Here we report the discovery of a rice diterpenoid gene cluster on chromosome 7 (DGC7) encoding the entire biosynthetic pathway to 5,10-diketo-casbene, a member of the mono-cyclic casbene-derived diterpenoids. We revealed that DGC7 is regulated through MeJA mediated epigenetic control directly by JMJ705 3 . Functional characterization of pathway genes revealed OsCYP71Z21 to encode a casbene C10 oxidase, sought after for the biosynthesis of an array of medicinally important

Coronaviruses are enveloped, single-stranded RNA viruses that are distributed worldwide. They include transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), and the human coronaviruses severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), many of which seriously endanger human health and well-being. Only alphacoronaviruses and betacoronaviruses harbor nonstructural protein 1 (nsp1), which performs multiple functions in inhibiting antiviral host responses. The role of the C terminus of betacoronavirus nsp1 in virulence has been characterized, but the location of the alphacoronavirus nsp1 region that is important for virulence remains unclear. Here, using TGEV nsp1 as a model to explore the function of this protein in alphacoronaviruses, we demonstrate that alphacoronavirus nsp1 inhibits host gene expression. Solving the crystal structure of full-length TGEV at 1.85-Å resolution and conducting several biochemical analyses, we observed that a specific motif (amino acids 91-95) of alphacoronavirus nsp1 is a conserved region that inhibits host protein synthesis. Using a reverse-genetics system based on CRISPR/ Cas9 technology to construct a recombinant TGEV in which this specific nsp1 motif was altered, we found that this mutation does not affect virus replication in cell culture but significantly reduces TGEV pathogenicity in pigs. Taken together, our findings suggest that alphacoronavirus nsp1 is an essential virulence determinant, providing a potential paradigm for the development of a new attenuated vaccine based on modified nsp1.

Porcine epidemic diarrhea virus (PEDV), a member of the genus Alphacoronavirus, has caused significant damage to the Asian and American pork industries. Coronavirus 3C-like protease (3CL(pro)), which is involved in the processing of viral polyproteins for viral replication, is an appealing antiviral drug target. Here, we present the crystal structures of PEDV 3CL(pro) and a molecular complex between an inactive PEDV 3CL(pro) variant C144A bound to a peptide substrate. Structural characterization, mutagenesis and biochemical analysis reveal the substrate-binding pockets and the residues that comprise the active site of PEDV 3CL(pro). The dimerization of PEDV 3CL(pro) is similar to that of other Alphacoronavirus 3CL(pro)s but has several differences from that of SARS-CoV 3CL(pro) from the genus Betacoronavirus. Furthermore, the non-conserved motifs in the pockets cause different cleavage of substrate between PEDV and SARS-CoV 3CL(pro)s, which may provide new insights into the recognition of substrates by 3CL(pro)s in various coronavirus genera.

Porcine reproductive and respiratory syndrome virus (PRRSV) RNA endoribonuclease nsp11 belongs to the XendoU superfamily and plays a crucial role in arterivirus replication. Here, we report the first crystal structure of the arterivirus nsp11 protein from PRRSV, which exhibits a unique structure and assembles into an asymmetric dimer whose structure is completely different from the hexameric structure of coronavirus nsp15. However, the structures of the PRRSV nsp11 and coronavirus nsp15 catalytic domains were perfectly superimposed, especially in the “active site loop” (His129 to His144) and “supporting loop” (Val162 to Thr179) regions. Importantly, our biochemical data demonstrated that PRRSV nsp11 exists mainly as a dimer in solution. Mutations of the major dimerization site determinants (Ser74 and Phe76) in the dimerization interface destabilized the dimer in solution and severely diminished endoribonuclease activity, indicating that the dimer is the biologically functional unit. In the dimeric structure, the active site loop and supporting loop are packed against one another and stabilized by monomer-monomer interactions. These findings may help elucidate the mechanism underlying arterivirus replication and may represent great potential for the development of antiviral drugs.IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is a member of the family Arteriviridae, order Nidovirales. PRRSV is a major agent of respiratory diseases in pigs, causing tremendous economic losses to the swine industry worldwide. The PRRSV nsp11 endoribonuclease plays a vital role in arterivirus replication, but its precise roles and mechanisms of action are poorly understood. Here, we report the first dimeric structure of the arterivirus nsp11 from PRRSV at 2.75-Å resolution. Structural and biochemical experiments demonstrated that nsp11 exists mainly as a dimer in solution and that nsp11 may be fully active as a dimer. Mutagenesis and structural analysis revealed NendoU active site residues, which are conserved throughout the order Nidovirales (families Arteriviridae and Coronaviridae) and the major determinants of dimerization (Ser74 and Phe76) in Arteriviridae. Importantly, these findings may provide a new structural basis for antiviral drug development.