Rice (Oryza sativa L.) is a chilling-sensitive staple crop that originated in subtropical regions of Asia. Introduction of the chilling tolerance trait enables the expansion of rice cultivation to temperate regions. Here we report the cloning and characterization of HAN1, a quantitative trait locus (QTL) that confers chilling tolerance on temperate japonica rice. HAN1 encodes an oxidase that catalyzes the conversion of biologically active jasmonoyl-L-isoleucine (JA-Ile) to the inactive form 12-hydroxy-JA-Ile (12OH-JA-Ile) and fine-tunes the JA-mediated chilling response. Natural variants in HAN1 diverged between indica and japonica rice during domestication. A specific allele from temperate japonica rice, which gained a putative MYB cis-element in the promoter of HAN1 during the divergence of the two japonica ecotypes, enhances the chilling tolerance of temperate japonica rice and allows it to adapt to a temperate climate. The results of this study extend our understanding of the northward expansion of rice cultivation and provide a target gene for the improvement of chilling tolerance in rice.

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Cyadox (CYX), (2-formylquinoxaline)-N(1),N(4)-dioxide cyanoacetylhydrazone, is a growth promoter, which is more efficient and less toxic to animals. Few studies have been performed to reveal the metabolism of CYX in animals till now. In this study, the metabolic fate of CYX in the liver microsomes of animal was investigated firstly using high-performance liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry. CYX was incubated with rat, chicken and pig liver microsomes in the presence of a NADPH-generating system. Multiple scans of metabolites in MS and MS(2) modes and accurate mass measurements were performed simultaneously through data-dependent acquisition. Most measured mass errors were less than 10 ppm for both protonated molecules and fragment ions using external mass calibration. The structures of metabolites and their fragment ions were easily and reliably characterized based on the accurate MS(2) spectra and known structure of CYX. The relative biotransformation of CYX into characterized metabolites was estimated based on the UV absorption and the assumption that all metabolites had the same extinction coefficient as the parent compound at 305 nm. Totally, seven metabolites were identified as three reduced metabolites (cyadox 1-monoxide (Cy1), cyadox 4-monoxide (Cy2) and bisdesoxycyadox (Cy4)), three hydrolysis metabolites of the amide bond (N-decyanoacetyl cyadox (Cy5), N-decyanoacetyl cyadox 1-monoxide (Cy6) and N-decyanoacetyl bisdesoxycyadox (Cy7)) and a hydroxylation metabolite of Cy1 (Cy3). Cy1-Cy6 could be detected in rat, chicken and pig liver microsomes while metabolite Cy7 could only be observed in pig. The amounts of the metabolites in three species are different. For the formations of Cy1 and Cy3, the rank order was rat approximately chicken > pig. For Cy4 and Cy5, the order was pig > rat > chicken. Cy1 and Cy4 have been previously reported, whereas the other five metabolites were novel. The N-->O group reduction and hydroxylation were the main metabolic pathways for CYX in the three species.