Calcium-Promoted Interaction between the C2-Domain Protein EHB1 and Metal Transporter IRT1 Inhibits Arabidopsis Iron Acquisition

Khan, Imran; Grätz, R.; Denezhkin, Polina; Schott‐Verdugo, Stephan; Angrand, Kalina; Genders, Lara; Basgaran, Rubek Merina; Fink‐Straube, Claudia; Brumbarova, Tzvetina; Gohlke, Holger; Bauer, Petra; Ivanov, Rumen

doi:10.1104/pp.19.00163

Cited by 35 publications

(75 citation statements)

References 72 publications

(131 reference statements)

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“…Our finding has interesting implications regarding the Fe deficiency‐induced signaling cascade. It is tempting to speculate that the cytoplasmic retention of bHLH039 could be linked to direct crosstalk at protein level with other Fe deficiency‐related proteins that are localized at the plasma membrane, such as the effectors FRO2 and IRT1, and/or the Fe response modulators CBL1/9 (Gratz, Manishankar, et al, ) and EHB1 (Khan et al, ). Posttranslational control plays a prominent role in the functioning of bHLH039 and potentially the other three group Ib bHLH proteins involved in Fe acquisition and homeostasis.…”

Section: Discussionmentioning

confidence: 99%

Mobility and localization of the iron deficiency‐induced transcription factor bHLH039 change in the presence of FIT

et al. 2019

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Regulation of iron (Fe) acquisition and homeostasis is critical for plant survival. In Arabidopsis, Fe deficiency‐induced bHLH039 forms a complex with the master regulator FIT and activates it to upregulate Fe acquisition genes. FIT is partitioned between cytoplasm and nucleus, whereby active FIT accumulates more in the nucleus than inactive FIT. At the same time, there is so far no information on the subcellular localization of bHLH039 protein and how it is controlled. We report here that the bHLH039 localization pattern changes depending on the presence of FIT in the cell. When expressed in cells lacking FIT, bHLH039 localizes predominantly in the cytoplasm, including cytoplasmic foci in close proximity to the plasma membrane. The presence of FIT enhances the mobility of bHLH039 and redirects the protein toward primarily nuclear localization, abolishing its accumulation in cytoplasmic foci. This FIT‐dependent change in localization of bHLH039 found in transient fluorescent protein expression experiments was confirmed in both leaves and roots of Arabidopsis transgenic plants, stably expressing hemagglutinin‐tagged bHLH039 in wild‐type or fit mutant background. This posttranslational mechanism for intracellular partitioning of Fe‐responsive transcription factors suggests a signaling cascade that translates Fe sensing at the plasma membrane to nuclear accumulation of the transcriptional regulators.

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Section: Discussionmentioning

confidence: 99%

Mobility and localization of the iron deficiency‐induced transcription factor bHLH039 change in the presence of FIT

et al. 2019

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“…After root reorientation and subsequent statolith sedimentation movement, a Ca 2+ ‐signal derived from an asymmetrically Ca 2+ ‐release within the statocytes is triggered, which activates EHB1 and AGD12. Ca 2+ ‐bound EHB1 gets attached to the membrane comparable to the inhibitory function of EHB1 recently described for iron uptake (Khan et al, 2019) and either affects or competes with AGD12 for ARF‐binding. Activated EHB1 can either directly affect/inhibit AGD12 or competes with the protein for ARF binding.…”

Section: Discussionmentioning

confidence: 53%

“…Because of the intriguing homology of the C‐terminal parts of AGD12 and EHB1 and their antagonistic interaction in phototropic and gravitropic bending, we hypothesize that AGD12 might act as a default element for ARF‐driven GTP hydrolysis ensuring normal endosomal traffic, while EHB1 acts as an inhibitory element by binding to ARF counteracting this way ARF‐GAP activity. Recently, it was shown that Ca 2+ ‐bound EHB1 attaches to the membrane and inhibits iron uptake by interacting with the iron‐regulated transporter IRT1 in Arabidopsis (Khan et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

A gravitropic stimulus alters the distribution of EHB1, a negative effector of root gravitropism in Arabidopsis

et al. 2020

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In Arabidopsis gravitropism is affected by two antagonistically interacting proteins, AGD12 (ADP‐RIBOSYLATION FACTOR GTPase‐ACTIVATING PROTEIN) and EHB1 (ENHANCED BENDING 1). While AGD12 enhances gravitropic bending, EHB1 functions as a negative element. To further characterize their cellular function, we analyzed the location of AGD12‐GFP and EHB1‐GFP fusion proteins in the root apex by confocal laser‐scanning microscopy after gravitropic stimulation. For this purpose, a novel method of microscopic visualization was developed with the objective and root axes aligned allowing an improved and comparable discernment of the fluorescence gradient across the columella. In vertical roots, both proteins were localized symmetrically and occurred preferentially in the outer layers of the columella. After reorienting roots horizontally, EHB1‐GFP accumulated in the upper cell layers of the columella, that is, opposite to the gravity vector. The gravity‐induced EHB1‐GFP asymmetry disappeared after reorienting the roots back into the vertical position. No such asymmetry occurred with AGD12‐GFP. Our findings reveal that after a gravitropic stimulus the cellular ratio between EHB1 and AGD12 is affected differently in the upper and lower part of the root. Its impact as a significant signaling event that ultimately affects the redirection of the lateral auxin flux toward the lower site of the root is discussed.

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“…At present, it is unclear whether CME is the only mode of IRT1 endocytosis, and data on a recently described IRT1‐interacting protein may suggest the existence of alternative pathways. The C2 domain‐containing small peripheral membrane protein ENHANCED BENDING1 (EHB1) was recently identified as an IRT1 inhibitor [Khan et al., 2019] (Figure 2A). In the presence of calcium, EHB1 associates to phosphatidylinositol (PI) and phosphatidylinositol 4‐phosphate (PI4P) lipid heads on the plasma membrane cytoplasmic side.…”

Section: Cme and Ubiquitin Regulate Metal Transporter Internalisationmentioning

confidence: 99%

Endocytosis in plants: Peculiarities and roles in the regulated trafficking of plant metal transporters

Ivanov

Vert

2020

Biology of the Cell

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The removal of transmembrane proteins from the plasma membrane via endocytosis has emerged as powerful strategy in the regulation of receptor signalling and molecule transport. In the last decade, IRON‐REGULATED TRANSPORTER1 (IRT1) has been established as one of the key plant model proteins for studying endomembrane trafficking. The use of IRT1 and additional other metal transporters has uncovered novel factors involved in plant endocytosis and facilitated a better understanding of the role of endocytosis in the fine balancing of plant metal homoeostasis. In this review, we outline the specifics of plant endocytosis compared to what is known in yeast and mammals, and based on several examples, we demonstrate how studying metal transport has contributed to extending our knowledge of endocytic trafficking by shedding light on novel regulatory mechanisms and factors.

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Calcium-Promoted Interaction between the C2-Domain Protein EHB1 and Metal Transporter IRT1 Inhibits Arabidopsis Iron Acquisition

Cited by 35 publications

References 72 publications

Mobility and localization of the iron deficiency‐induced transcription factor bHLH039 change in the presence of FIT

Mobility and localization of the iron deficiency‐induced transcription factor bHLH039 change in the presence of FIT

A gravitropic stimulus alters the distribution of EHB1, a negative effector of root gravitropism in Arabidopsis

Endocytosis in plants: Peculiarities and roles in the regulated trafficking of plant metal transporters

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