@article{6645cb3950be4ef1952338a9c43742d0,
title = "The role of rice phenolics efflux transporter in solubilizing apoplasmic iron",
abstract = "Iron (Fe) is an essential micronutrient for plants whose deficiency presents a major worldwide agricultural problem. Moreover, Fe is not easily available in neutral to alkaline soils, rendering plants deficient in Fe despite its abundance. Plants secrete phenolics, such as protocatechuic acid (PCA) and caffeic acid (CA), to take up and utilize apoplasmic precipitated Fe, but despite the rapid progress in understanding cellular and subcellular Fe transport, the molecular mechanisms of phenolics synthesis and secretion are not clear. Recently, we isolated and characterized a phenolics efflux transporter in rice by characterizing a mutant in which the amount of PCA and CA in the xylem sap was dramatically reduced, which we hence named phenolics efflux zero 1 (pez1). PEZ1 is a plasma membrane protein that transports PCA when expressed in Xenopus laevis oocytes, and characterization of PEZ1 knockdown and overexpressing plants revealed that it plays an essential role in solubilizing precipitated apoplasmic Fe. The identification of PEZ1 will increase our understanding of apoplasmic Fe solubilization as well as promote research on phenolics efflux mechanisms in different organisms.",
keywords = "Iron, Oryza sativa, Phenolics transport, Protocatechuic acid, Xylem sap",
author = "Yasuhiro Ishimaru and Khurram Bashir and Hiromi Nakanishi and Nishizawa, {Naoko K.}",
note = "Funding Information: trollingthemovementoAs suberin plays an impor%fsolutant roPtes,le in c19theonOth-wiPe xyleth or wUm sap withoEas lout CdJw. FTer thae conUn icenSn thtratJe Wion iCT, n Vsolubof PCUilizA iFation of precipitated apoplasmic n the pez1-2mutant impairs the role of phenolics in controlling water and while no difference was observed for xylem Fe in the stele, and thus, the low availabil-mineral transport cannot be overlooked. Cd and Mn. Significant differences in the ity of Fe leads to the induction of OsIRT1. Thus, understanding the molecular mech-localization of insoluble Fe were observed As PEZ1 and OsIRT1 co-localize in the anism of phenolics efflux transport is cru-when leaf samples were stained with Perl{\textquoteright}s stele, the PCA secretion may comple-cial for developing strategies to mitigate solution to examine the localization of ment Fe2+ uptake by OsIRT1 and seems widespread Fe deficiency. Fe. These results suggested a clear role of to be an integral part of the Fe2+ uptake PEZ1 was isolated in an effort to char-PEZ1 in solubilizing precipitated apoplas-system in rice (Fig. 2). In contrast, the acterize T-DNA mutants for genes regu-mic Fe.21 increase in phenolics secretion in PEZ1-lated by cadmium (Cd). PEZ1 belongs to Secretion of excess PCA strongly overexpressing plants increases the solu-the multidrug and toxic compound extru-solubilizes Fe precipitated in the stele, bilization of apoplasmic Fe, and plants sion transporter family whose members leading to symptoms of Fe excess. The showed an increased tolerance to Fe defi-transport small organic compounds.20 analysis of PEZ1 overexpression lines ciency in alkaline soils. The identification The substrates of PEZ1 were identified confirmed this hypothesis. PEZ1 over-of PEZ1 is an important step that helps in by analyzing liquid chromatography/ expression lines accumulated higher better understanding the solubilization of mass spectrometry data profiles of the amounts of Fe in roots and leaves owing apoplasmic Fe and will generate research xylem sap of pez1-1 and pez1-2 mutants. to the high solubilization of precipitated on phenolics efflux mechanisms in other The data indicated that PEZ1 transports apoplasmic stele Fe, and as a result, plants. PCA and caffeic acid (CA). Furthermore, the growth of these lines was severely PEZ1 transported radiolabeled PCA when restricted. In contrast, PEZ1 overexpres-expressed in Xenopus laevis oocytes. PEZ1 sion lines grew better than the WT in This work was supported by the localizes to the plasma membrane in rice calcareous soil, showing that in these Programme for Promotion of Basic root cells, as well as in rice root hairs and lines, PCA-solubilized Fe is available Research Activities for Innovative onion epidermal cells. The pez1-2 mutant under Fe-limiting conditions. Biosciences (PROBRAIN) and a grant accumulated more Fe in the roots, but The expression of PEZ1 is regulated from the Ministry of Agriculture, Forestry not in the leaves, compared to wild-type by Cd, and both of the PEZ1 knock-and Fisheries of Japan (Genomics for (WT) plants; the differences were greater down mutants accumulated higher Cd Agricultural Innovation, GMB0001).",
year = "2011",
month = oct,
doi = "10.4161/psb.6.10.17694",
language = "English",
volume = "6",
pages = "1624--1626",
journal = "Plant Signaling and Behavior",
issn = "1559-2316",
publisher = "Landes Bioscience",
number = "10",
}