0 avis
Direct metal sensing by the bifunctional IRT1 iron transporter/receptor
Archive ouverte
Edité par CCSD -
International audience. Plants have evolved sophisticated strategies to constantly monitor and respond to ever changing environmental conditions. The iron transporter IRT1 is the major root metal transporter responsible for iron uptake in plants, but also transports other metals such as zinc, manganese, cobalt or cadmium. Since metal availability in soils greatly varies in time and space, plant roots need to adjust IRT1 levels to provide enough iron for metabolism and avoid overaccumulation of highly-reactive non-iron metals. Our recent work uncovered that IRT1 is rapidly degraded by endocytosis and targeting to the vacuole upon non-iron metal excess (Dubeaux et al., 2018 Molecular Cell). This involves phosphorylation of IRT1 by the CIPK23 kinase and subsequent recruitment of the IDF1 E3 ligase to mediate K63 polyubiquitination and vacuolar targeting of IRT1. Failure to phosphorylate (i.e. cipk23 mutant background, or mutation of target phosphorylation sites in IRT1) or to ubiquitinate (i.e. idf1 mutant background, or mutation of target ubiquitination sites) result in cell surface stabilization of IRT1 and hypersensitivity to metals. We recently observed that IRT1 works as a bifunctional transporter-receptor, capable not only to transport metals but also to directly sense metal flux through the plasma membrane. NMR and mass spectrometry analyses revealed that IRT1 senses metals through binding to several amino acids located nearby the phosphorylation and ubiquitination sites in a cytosolic loop of IRT1. Mutation of a histidine-rich domain driving metal biding in IRT1 does not impact IRT1 transport activity but rather abolishes the ability of IRT1 to recruit CIPK23. IRT1 therefore acts as a transceptor, capable of initiating a short signaling pathway that culminates in its own degradation. This sophisticated mechanism allows plants to maximize iron uptake while limiting the accumulation of potentially noxious heavy metals.
Consulter en ligne
Suggestions
Du même auteur
