Background Metal homeostasis is critical for plant growth, development and adaptation to environmental stresses and largely governed by a variety of metal transporters. The plant ZIP ( Z n-regulated transporter, I ron-regulated transporter-like P rotein) family proteins belong to the integral membrane transporters responsible for uptake and allocation of essential and non-essential metals. However, whether the ZIP family members mediate metal efflux and its regulatory mechanism remains unknown. Results In this report, we provided evidence that OsZIP1 is a metal-detoxified transporter through preventing excess Zn, Cu and Cd accumulation in rice. OsZIP1 is abundantly expressed in roots throughout the life span and sufficiently induced by excess Zn, Cu and Cd but not by Mn and Fe at transcriptional and translational levels. Expression of OsZIP-GFP fusion in rice protoplasts and tobacco leaves shows that OsZIP1 resides in the endoplasmic reticulum (ER) and plasma membrane (PM). The yeast ( Saccharomyces cerevisiae ) complementation test shows that expression of OsZIP1 reduced Zn accumulation. Transgenic rice overexpressing OsZIP1 grew better under excess metal stress but accumulated less of the metals in plants. In contrast, both oszip1 mutant and RNA interference (RNAi) lines accumulated more metal in roots and contributed to metal sensitive phenotypes. These results suggest OsZIP1 is able to function as a metal exporter in rice when Zn, Cu and Cd are excess in environment. We further identified the DNA methylation of histone H3K9me2 of OsZIP1 and found that OsZIP1 locus, whose transcribed regions imbed a 242 bp sequence, is demethylated, suggesting that epigenetic modification is likely associated with OsZIP1 function under Cd stress. Conclusion OsZIP1 is a transporter that is required for detoxification of excess Zn, Cu and Cd in rice. Electronic supplementary material The online version of this article (10.1186/s12870-019-1899-3) contains supplementary material, which is available to authorized users.

Quinolinate phosphoribosyltransferase (QAPRTase, EC 2.4.2.19) catalyzes the formation of nicotinate mononucleotide, carbon dioxide, and pyrophosphate from 5-phosphoribosyl 1-pyrophosphate (PRPP) and quinolinic acid (QA, pyridine 2,3-dicarboxylic acid). The enzyme is the only type II PRTase whose X-ray structure is known. Here we determined the kinetic mechanism of the enzyme from Salmonella typhimurium. Equilibrium binding studies show that PRPP and QA each form binary complexes with the enzyme, with K D values (53 and 21 µM, respectively) similar to their K M values (30 and 25 µM, respectively). Although neither PP i nor NAMN products bound well to the enzyme, 130-fold tighter binding of PP i (K D ) 75 µM) and NAMN (K D ) 6 µM) in a ternary complex was observed. Phthalic acid (K D ) 21 µM) and PRPP each caused a 2.5-fold tightening of the other's binding. Isotope trapping experiments indicated that the E‚QA complex is catalytically competent, whereas the E‚PRPP complex could not be trapped. Pre-steady-state kinetics gave a linear rate of NAMN formation, indicating that on-enzyme phosphoribosyl transfer chemistry is rate-determining. Isotope trapping from the steady state revealed that nearly all QA and about one-third of PRPP in ternary enzyme‚QA‚PRPP complexes could be trapped as the product. Substrate inhibition by PRPP was observed. These data demonstrate a predominantly ordered kinetic mechanism in which productive binding of quinolinic acid precedes that of PRPP. An E‚PRPP complex exists as a nonproductive side branch.

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Methane-rich water triggered adventitious rooting by regulating heme oxygenase1/carbon monoxide and calcium pathways in cucumber explants. Heme oxygenase1/carbon monoxide (HO1/CO) and calcium (Ca(2+)) were reported as the downstream signals in auxin-induced cucumber adventitious root (AR) formation. Here, we observed that application of methane-rich water (MRW; 80% saturation) obviously induced AR formation in IAA-depleted cucumber explants. To address the universality, we checked adventitious rooting in soybean and mung bean explants, and found that MRW (50 and 10% saturation, respectively) exhibited the similar inducing results. To further determine if the HO1/CO system participated in MRW-induced adventitious rooting, MRW, HO1 inducer hemin, its activity inhibitor zinc protoporphyrin IX (ZnPP), and its catalytic by-products CO, bilirubin, and Fe(2+) were used to detect their effects on cucumber adventitious rooting in IAA-depleted explants. Subsequent results showed that MRW-induced adventitious rooting was blocked by ZnPP and further reversed by 20% saturation CO aqueous solution. However, the other two by-products of HO1, bilirubin and Fe(2+), failed to induce AR formation. Above responses were consistent with the MRW-induced increases of HO1 transcript and corresponding protein level. Further molecular evidence indicted that expression of marker genes, including auxin signaling-related genes and cell cycle regulatory genes, were modulated by MRW alone but blocked by the cotreatment with ZnPP, the latter of which could be significantly rescued by the addition of CO. By using the Ca(2+)-channel blocker and Ca(2+) chelator, the involvement of Ca(2+) pathway in MRW-induced adventitious rooting was also suggested. Together, our results indicate that MRW might serve as a stimulator of adventitious rooting, which was partially mediated by HO1/CO and Ca(2+) pathways.