Metallochaperones are key proteins for the safe transport of metallic ions inside the cell. HIPPs (heavy metal-associated isoprenylated plant proteins) are metallochaperones that contain a metal binding domain (HMA) and a C-terminal isoprenylation motif. In this study, we provide evidence that proteins of this family are found only in vascular plants and may be separated into five distinct clusters. HIPPs may be involved in (a) heavy metal homeostasis and detoxification mechanisms, especially those involved in cadmium tolerance, (b) transcriptional responses to cold and drought, and (c) plant-pathogen interactions. In particular, our results show that the rice (Oryza sativa) HIPP OsHIPP41 gene is highly expressed in response to cold and drought stresses, and its product is localized in the cytosol and the nucleus. The results suggest that HIPPs play an important role in the development of vascular plants and in plant responses to environmental changes.

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HighlightGenetic factors associated with boron toxicity tolerance in rice were explored through an integrated approach combining genome-wide association study and transcriptomics.

Monitoring of ozone damage to crops plays an increasingly important role for the food security of many developing countries. Ethylenediurea (EDU) could be a tool to assess ozone damage to vegetation on field scale, but its physiological mode of action remains unclear. This study investigated mechanisms underlying the ozone-protection effect of EDU in controlled chamber experiments. Ozone sensitive and tolerant rice genotypes were exposed to ozone (108 ppb, 7 hr day ) and control conditions. EDU alleviated ozone effects on plant morphology, foliar symptoms, lipid peroxidation, and photosynthetic parameters in sensitive genotypes. Transcriptome profiling by RNA sequencing revealed that thousands of genes responded to ozone in a sensitive variety, but almost none responded to EDU. Significant interactions between ozone and EDU application occurred mostly in ozone responsive genes, in which up-regulation was mitigated by EDU application. Further experiments documented ozone degrading properties of EDU, as well as EDU deposits on leaf surfaces possibly related to surface protection. EDU application did not mitigate the reaction of plants to other abiotic stresses, including iron toxicity, zinc deficiency, and salinity. This study provided evidence that EDU is a surface protectant that specifically mitigates ozone stress without interfering directly with the plants' stress response systems.

Plants are exposed to a wide range of abiotic stresses (AS), which often occur in combination. Because physiological investigations typically focus on one stress, our understanding of unspecific stress responses remains limited. The plant redox homeostasis, i.e., the production and removal of reactive oxygen species (ROS), may be involved in many environmental stress conditions. Therefore, this study intended to identify genes, which are activated in diverse AS, focusing on ROS-related pathways. We conducted a meta-analysis (MA) of microarray experiments, focusing on rice. Transcriptome data were mined from public databases and fellow researchers, which represented 36 different experiments and investigated diverse AS, including ozone stress, drought, heat, cold, salinity, and mineral deficiencies/toxicities. To overcome the inherent artifacts of different MA methods, data were processed using Fisher, rOP, REM, and product of rank (GeneSelector), and genes identified by most approaches were considered as shared differentially expressed genes (DEGs). Two MA strategies were adopted: first, datasets were separated into shoot, root, and seedling experiments, and these tissues were analyzed separately to identify shared DEGs. Second, shoot and seedling experiments were classed into oxidative stress (OS), i.e., ozone and hydrogen peroxide treatments directly producing ROS in plant tissue, and other AS, in which ROS production is indirect. In all tissues and stress conditions, genes a priori considered as ROS-related were overrepresented among the DEGs, as they represented 4% of all expressed genes but 7–10% of the DEGs. The combined MA approach was substantially more conservative than individual MA methods and identified 1001 shared DEGs in shoots, 837 shared DEGs in root, and 1172 shared DEGs in seedlings. Within the OS and AS groups, 990 and 1727 shared DEGs were identified, respectively. In total, 311 genes were shared between OS and AS, including many regulatory genes. Combined co-expression analysis identified among those a cluster of 42 genes, many involved in the photosynthetic apparatus and responsive to drought, iron deficiency, arsenic toxicity, and ozone. Our data demonstrate the importance of redox homeostasis in plant stress responses and the power of MA to identify candidate genes underlying unspecific signaling pathways.