HLB1 Is a Tetratricopeptide Repeat Domain-Containing Protein That Operates at the Intersection of the Exocytic and Endocytic Pathways at the TGN/EE in Arabidopsis

Sparks, Jeffrey A.; Kwon, Taegun; Renna, Luciana; Liao, Fuqi; Brandizzí, Federica; Blancaflor, Elison B.

doi:10.1105/tpc.15.00794

Cited by 27 publications

(31 citation statements)

References 124 publications

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“…In addition to ARFs and AGD1, potential components of the ARF-GTPase machinery that drive root hair development are the ARF-GEFs GNOM (also known as GN) and BEN1/MIN7 (Nomura et al, 2006;Tanaka et al, 2009;Naramoto et al, 2010Naramoto et al, , 2014. Whereas ben1/min7 mutants were recently shown to exhibit root hair shape defects (Sparks et al, 2016), GNOM and GNOM-like (GNL) ARF-GEFs are required for root hair planar polarity (Fischer et al, 2006). Moreover, GNOM was shown to be involved in root hair tip growth and GNOM-GFP localizes to trichoblasts during early bulge formation, where it is a direct BFA target (Richter et al, 2011;Stanislas et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

Deletion analysis of AGD1 reveals domains crucial for plasma membrane recruitment and function in root hair polarity

Yoo

Naramoto

Sparks

et al. 2018

Journal of Cell Science

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AGD1, a plant ACAP-type ADP-ribosylation factor-GTPase activating protein (ARF-GAP), functions in specifying root hair polarity in To better understand how AGD1 modulates root hair growth, we generated full-length and domain-deleted AGD1-green fluorescent protein (GFP) constructs, and followed their localization during root hair development. AGD1-GFP localized to the cytoplasm and was recruited to specific regions of the root hair plasma membrane (PM). Distinct PM AGD1-GFP signal was first detected along the site of root hair bulge formation. The construct continued to mark the PM at the root hair apical dome, but only during periods of reduced growth. During rapid tip growth, AGD1-GFP labeled the PM of the lateral flanks and dissipated from the apical-most PM. Deletion analysis and a single domain GFP fusion revealed that the pleckstrin homology (PH) domain is the minimal unit required for recruitment of AGD1 to the PM. Our results indicate that differential recruitment of AGD1 to specific PM domains is an essential component of the membrane trafficking machinery that facilitates root hair developmental phase transitions and responses to changes in the root microenvironment.

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Section: Discussionmentioning

confidence: 99%

Deletion analysis of AGD1 reveals domains crucial for plasma membrane recruitment and function in root hair polarity

Yoo

Naramoto

Sparks

et al. 2018

Journal of Cell Science

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“…Only diffuse fluorescence was observed in the central columella of both reporter lines ( Figure 3A; Baluska et al, 1997;Blancaflor, 2013). Lifeact-mGFP and GFP-ABD2-GFP also labeled extensive F-actin arrays in growing root hairs that were reminiscent of F-actin organization in A. thaliana lines expressing these two reporters ( Figure 3B; Dyachok et al, 2014;Sparks et al, 2016). Moreover, other cell types in transgenic lines expressing GFP-ABD2-GFP and Lifeact-mGFP including guard cells, minor leaf veins and epidermal cells in nodules exhibited dense F-actin arrays (Figures 3C-E).…”

Section: Lifeact-mgfp and Gfp-abd2-gfp Reporters Decorate Extensive Fmentioning

confidence: 98%

“…Each of the cropped images was processed by canceling the background noise followed by marking F-actin with one pixelwide lines following the methods described in (Wang et al, 2008;Vidali et al, 2009;Dyachok et al, 2014;Sparks et al, 2016). Eccentricity was calculated from compact ellipse sections from cropped root images.…”

Section: Quantification Of F-actin Organization and Dynamics Of Z Mamentioning

confidence: 99%

“…Therefore, we next asked if effects of eBL on F-actin would be more obvious in living roots. To address this question, transgenic M. truncatula plants that expressed two live cell F-actin reporters (Lifeact-mGFP and GFP-ABD2-GFP) under the control of the ubiquitin 10 (UBQ10) promoter were generated (Wang et al, 2008;Vidali et al, 2009;Dyachok et al, 2014;Sparks et al, 2016). Before using the lines for clinorotation assays, we first examined the quality of F-actin labeling in seedling roots.…”

Section: Lifeact-mgfp and Gfp-abd2-gfp Reporters Decorate Extensive Fmentioning

confidence: 99%

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Brassinosteroids Inhibit Autotropic Root Straightening by Modifying Filamentous-Actin Organization and Dynamics

et al. 2020

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When positioned horizontally, roots grow down toward the direction of gravity. This phenomenon, called gravitropism, is influenced by most of the major plant hormones including brassinosteroids. Epi-brassinolide (eBL) was previously shown to enhance root gravitropism, a phenomenon similar to the response of roots exposed to the actin inhibitor, latrunculin B (LatB). This led us to hypothesize that eBL might enhance root gravitropism through its effects on filamentous-actin (F-actin). This hypothesis was tested by comparing gravitropic responses of maize (Zea mays) roots treated with eBL or LatB. LatB-and eBL-treated roots displayed similar enhanced downward growth compared with controls when vertical roots were oriented horizontally. Moreover, the effects of the two compounds on root growth directionality were more striking on a slowly-rotating twodimensional clinostat. Both compounds inhibited autotropism, a process in which the root straightened after the initial gravistimulus was withdrawn by clinorotation. Although eBL reduced F-actin density in chemically-fixed Z. mays roots, the impact was not as strong as that of LatB. Modification of F-actin organization after treatment with both compounds was also observed in living roots of barrel medic (Medicago truncatula) seedlings expressing genetically encoded F-actin reporters. Like in fixed Z. mays roots, eBL effects on F-actin in living M. truncatula roots were modest compared with those of LatB. Furthermore, live cell imaging revealed a decrease in global F-actin dynamics in hypocotyls of etiolated M. truncatula seedlings treated with eBL compared to controls. Collectively, our data indicate that eBL-and LatB-induced enhancement of root gravitropism can be explained by inhibited autotropic root straightening, and that eBL affects this process, in part, by modifying F-actin organization and dynamics.

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“…F-actins provide the pushing force required for tubulation at the TGN membrane together with the Arp2/3 complex and myosin motor proteins (5,68). The plantspecific tetratricopeptide repeat domain-containing protein hypersensitive to latrunculin B1 (HLB1) associates with the TGN/ early endosome and tracks along actin filaments (69). The actin nucleation proteins, formins (70)(71)(72), and the heterodimeric capping protein (73) anchor the cytoskeleton to the endomembrane to regulate organelle morphology, especially the ER and Golgi.…”

Section: Protein Sorting To the Vacuole And Vacuole Morphology Arementioning

confidence: 99%

AP3M harbors actin filament binding activity that is crucial for vacuole morphology and stomatal closure in Arabidopsis

Zheng

Jiang

Wang

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Stomatal movement is essential for plant growth. This process is precisely regulated by various cellular activities in guard cells. F-actin dynamics and vacuole morphology are both involved in stomatal movement. The sorting of cargoes by clathrin adaptor protein (AP) complexes from the Golgi to the vacuole is critical for establishing a normal vacuole morphology. In this study, we demonstrate that the medium subunit of the AP3 complex (AP3M) binds to and severs actin filaments in vitro and that it participates in the sorting of cargoes (such as the sucrose exporter SUC4) to the tonoplast, and thereby regulates stomatal closure in Arabidopsis thaliana. Defects in AP3 or SUC4 led to more rapid water loss and delayed stomatal closure, as well as hypersensitivity to drought stress. In ap3m mutants, the F-actin status was altered compared to the wild type, and the sorted cargoes failed to localize to the tonoplast. AP3M contains a previously unidentified F-actin binding domain that is conserved in AP3M homologs in both plants and animals. Mutations in the F-actin binding domain of AP3M abolished its F-actin binding activity in vitro, leading to an aberrant vacuole morphology and reduced levels of SUC4 on the tonoplast in guard cells. Our findings indicate that the F-actin binding activity of AP3M is required for the precise localization of AP3-dependent cargoes to the tonoplast and for the regulation of vacuole morphology in guard cells during stomatal closure.

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HLB1 Is a Tetratricopeptide Repeat Domain-Containing Protein That Operates at the Intersection of the Exocytic and Endocytic Pathways at the TGN/EE in Arabidopsis

Cited by 27 publications

References 124 publications

Deletion analysis of AGD1 reveals domains crucial for plasma membrane recruitment and function in root hair polarity

Deletion analysis of AGD1 reveals domains crucial for plasma membrane recruitment and function in root hair polarity

Brassinosteroids Inhibit Autotropic Root Straightening by Modifying Filamentous-Actin Organization and Dynamics

AP3M harbors actin filament binding activity that is crucial for vacuole morphology and stomatal closure in Arabidopsis

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