Root vacuolar sequestration is one of the best-conserved plant strategies to cope with heavy metal toxicity. Here we report that zinc (Zn) tolerance in Arabidopsis requires the action of a novel Major Facilitator Superfamily (MFS) transporter. We show that ZIF2 (Zinc-Induced Facilitator 2) localises primarily at the tonoplast of root cortical cells and is a functional transporter able to mediate Zn efflux when heterologously expressed in yeast. By affecting plant tissue partitioning of the metal ion, loss of ZIF2 function exacerbates plant sensitivity to excess Zn, while its overexpression enhances Zn tolerance. The ZIF2 gene is Zn-induced and an intron retention event in its 5′UTR generates two splice variants (ZIF2.1 and ZIF2.2) encoding the same protein. Importantly, high Zn favours production of the longer ZIF2.2 transcript, which compared to ZIF2.1 confers greater Zn tolerance to transgenic plants by promoting higher root Zn immobilization. We show that the retained intron in the ZIF2 5′UTR enhances translation in a Zn-responsive manner, markedly promoting ZIF2 protein expression under excess Zn. Moreover, Zn regulation of translation driven by the ZIF2.2 5′UTR depends largely on a predicted stable stem loop immediately upstream of the start codon that is lost in the ZIF2.1 5′UTR. Collectively, our findings indicate that alternative splicing controls the levels of a Zn-responsive mRNA variant of the ZIF2 transporter to enhance plant tolerance to the metal ion.

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Botrytis umbel blight caused by Botrytis allii is a major disease that attacks onion crop. In vitro, Trichoderma viride, Penicillium chrysogenum, and Saccharomyces cerevisiae and extract of bitter apple fruits (Citrullus colocynthis) showed antagonistic effect and inhibited the mycelial growth of B. allii. Gas chromatography-mass spectrometry (GC-MS) analysis of bitter apple fruits showed the existence of 37 compounds and their derivatives. Among them, 10 compounds constituted 58.66% of the total analyses. Greenhouse experiment approved that the extract of bitter apple fruits was the most effective in reducing disease incidence and severity, followed by P. chrysogenum, when they were applied 2 days pre-inoculation with the pathogen. All treatments significantly increased the total phenolic contents than the untreated control, but the highest increase was obtained when S. cerevisiae and P. chrysogenum were applied. A positive correlation was found between the activity of bioagents and improvement of peroxidase and phenylalanine ammonia-lyase enzymes in onion plants to resist infection with the pathogen. P. chrysogenum caused the highest increase in polyphenoloxidase activity in infected onion plants, while S. cerevisiae showed the lowest level of this enzyme. The study approved that application of the bioagents not only protected the onions against Botrytis disease but also enhanced the content of antioxidant compounds in onions. This encourages the application of such preparations to manage the production of onion crop, especially in the organic farming that bans the application of any chemicals.