Natural variation in the HAN1 gene confers chilling tolerance in rice and allowed adaptation to a temperate climate.

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.

Genetic architecture of subspecies divergence in trace mineral accumulation and elemental correlations in the rice grain.

KEY MESSAGE: Genome differentiation has shaped the divergence in element concentration between rice subspecies and contributed to the correlation among trace minerals in the rice grain. The balance between trace minerals in rice, a staple food for more than half of the world's population, is crucial for human health. However, the genetic basis underlying the correlation between trace minerals has not been fully elucidated. To address this issue, we first quantified the concentrations of 11 trace minerals in the grains of a diversity panel of 575 rice cultivars. We found that eight elements were accumulated at significantly different levels between the indica and japonica subspecies, and we also observed significant correlation patterns among a number of elements. Further, using a genome-wide association study, we identified a total of 96 significant association loci (SALs). The differentiation of the major-effect SALs along with the different number of high-concentration alleles present in the two subspecies shaped the different element performance in indica and japonica varieties. Only a few SALs located in clusters and the majority of SALs showed subspecies/subgroup differentiation, indicating that the correlations between elements in the diversity panel were mainly caused by genome differentiation instead of shared genetic basis. The genetic architecture unveiled in this study will facilitate improvement in breeding for trace mineral content.

OsZIP7 functions in xylem loading in roots and inter-vascular transfer in nodes to deliver Zn/Cd to grain in rice.

Rice has lower zinc (Zn) but higher cadmium (Cd) content in grains than other staple crops. Understanding the molecular mechanisms involved in Zn and Cd transportation could benefit homeostatic control, facilitating optimisation of Zn and Cd levels to provide maximum nutrition and safety. In this study, we functionally characterised in planta the rice (Oryza sativa) transporter OsZIP7, which encodes a plasma membrane-localised protein with influx transport activity for both Zn and Cd. OsZIP7 was expressed in parenchyma cells of vascular bundles in roots and nodes. OsZIP7 knockout resulted in retention of Zn and Cd in roots and basal nodes, which hindered their upward delivery to upper nodes and brown rice. And a short-term labelling experiment with the stable 67Zn isotope showed that Zn was distributed toward roots and basal regions and away from leaves in the mutant compared with wild-type rice. Thus, OsZIP7 plays an integral role in xylem loading in roots and inter-vascular transfer in nodes to preferentially deliver Zn and Cd to developing tissues and rice grains.

Cultivar diversity and organ differences of cadmium accumulation in potato (Solanum tuberosum L.) allow the potential for Cd-safe staple food production on contaminated soils.

Cadmium (Cd) is a toxic element that can accumulate in plants and poses a threat to human health through biomagnification. There are differences in Cd levels among different plants tissues. Hence, an optimal crop that possesses low Cd levels in the edible parts but high levels in the inedible parts is urgently needed to simultaneously lower soil-Cd levels in contaminated fields and to produce Cd-safe crops. In this study, we investigated the Cd levels in tubers and other tissues of potato (Solanum tuberosum L.) using different experimental approaches, and identified variations in Cd accumulation in different potato cultivars and characterized the Cd-distribution pattern in potato. Our results showed that Cd accumulation in tubers of the tested cultivars varied greatly, and that tuber-Cd levels were much lower than in the stems or leaves. Two-way ANOVA revealed that the tuber-Cd levels in potato are determined by both genotypic differences and the soil-Cd levels of the farmlands. Among the cultivars tested, one cultivar, 'Eshu10', was found to have the lowest tuber-Cd levels but had much higher Cd levels in leaf and stem tissues. Our study shows that the Cd-distribution pattern within potato plants makes it an ideal candidate for the safe production of a staple food that also has the potential to contribute to the remediation of contaminated soils.