The boundary-expressed EPIDERMAL PATTERNING FACTOR-LIKE2 gene encoding a signaling peptide promotes cotyledon growth during Arabidopsis thaliana embryogenesis.

The shoot organ boundaries have important roles in plant growth and morphogenesis. It has been reported that a gene encoding a cysteine-rich secreted peptide of the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family, EPFL2, is expressed in the boundary domain between the two cotyledon primordia of Arabidopsis thaliana embryo. However, its developmental functions remain unknown. This study aimed to analyze the role of EPFL2 during embryogenesis. We found that cotyledon growth was reduced in its loss-of-function mutants, and this phenotype was associated with the reduction of auxin response peaks at the tips of the primordia. The reduced cotyledon size of the mutant embryo recovered in germinating seedlings, indicating the presence of a factor that acted redundantly with EPFL2 to promote cotyledon growth in late embryogenesis. Our analysis suggests that the boundary domain between the cotyledon primordia acts as a signaling center that organizes auxin response peaks and promotes cotyledon growth.

Establishment of the Embryonic Shoot Meristem Involves Activation of Two Classes of Genes with Opposing Functions for Meristem Activities.

The shoot meristem, a stem-cell-containing tissue initiated during plant embryogenesis, is responsible for continuous shoot organ production in postembryonic development. Although key regulatory factors including KNOX genes are responsible for stem cell maintenance in the shoot meristem, how the onset of such factors is regulated during embryogenesis is elusive. Here, we present evidence that the two KNOX genes STM and KNAT6 together with the two other regulatory genes BLR and LAS are functionally important downstream genes of CUC1 and CUC2, which are a redundant pair of genes that specify the embryonic shoot organ boundary. Combined expression of STM with any of KNAT6, BLR, and LAS can efficiently rescue the defects of shoot meristem formation and/or separation of cotyledons in cuc1cuc2 double mutants. In addition, CUC1 and CUC2 are also required for the activation of KLU, a cytochrome P450-encoding gene known to restrict organ production, and KLU counteracts STM in the promotion of meristem activity, providing a possible balancing mechanism for shoot meristem maintenance. Together, these results establish the roles for CUC1 and CUC2 in coordinating the activation of two classes of genes with opposite effects on shoot meristem activity.

Lateral root initiation requires the sequential induction of transcription factors LBD16 and PUCHI in Arabidopsis thaliana.

Lateral root (LR) formation in Arabidopsis thaliana is initiated by asymmetric division of founder cells, followed by coordinated cell proliferation and differentiation for patterning new primordia. The sequential developmental processes of LR formation are triggered by a localized auxin response. LATERAL ORGAN BOUNDARIES-DOMAIN 16 (LBD16), an auxin-inducible transcription factor, is one of the key regulators linking auxin response in LR founder cells to LR initiation. We identified key genes for LR formation that are activated by LBD16 in an auxin-dependent manner. LBD16 targets identified include the transcription factor gene PUCHI, which is required for LR primordium patterning. We demonstrate that LBD16 activity is required for the auxin-inducible expression of PUCHI. We show that PUCHI expression is initiated after the first round of asymmetric cell division of LR founder cells and that premature induction of PUCHI during the preinitiation phase disrupts LR primordium formation. Our results indicate that LR initiation requires the sequential induction of transcription factors LBD16 and PUCHI.

Mitochondrial Pyruvate Dehydrogenase Contributes to Auxin-Regulated Organ Development.

Pyruvate dehydrogenase is the first enzyme (E1) of the PDH complex (PDC). This multienzyme complex contains E1, E2, and E3 components and controls the entry of carbon into the mitochondrial tricarboxylic acid cycle to enable cellular energy production. The E1 component of the PDC is composed of an E1α catalytic subunit and an E1ß regulatory subunit. In Arabidopsis (Arabidopsis thaliana), there are two mitochondrial E1α homologs encoded by IAA-CONJUGATE-RESISTANT 4 (IAR4) and IAR4-LIKE (IAR4L), and one mitochondrial E1ß homolog. Although IAR4 was reported to be involved in auxin conjugate sensitivity and auxin homeostasis in root development, its precise role remains unknown. Here, we provide experimental evidence that mitochondrial PDC E1 contributes to polar auxin transport during organ development. We performed genetic screens for factors involved in cotyledon development and identified an uncharacterized mutant, macchi-bou 1 (mab1). MAB1 encodes a mitochondrial PDC E1ß subunit that can form both a homodimer and a heterodimer with IAR4. The mab1 mutation impaired MAB1 homodimerization, reduced the abundance of IAR4 and IAR4L, weakened PDC enzymatic activity, and diminished mitochondrial respiration. A metabolomics analysis showed significant changes in metabolites including amino acids in mab1 and, in particular, identified an accumulation of Ala. These results suggest that MAB1 is a component of the Arabidopsis mitochondrial PDC E1. Furthermore, in mab1 mutants and seedlings where the TCA cycle was pharmacologically blocked, we found reduced abundance of the PIN-FORMED (PIN) auxin efflux carriers, possibly due to impaired PIN recycling and enhanced PIN degradation in vacuoles. Therefore, we suggest that mab1 induces defective polar auxin transport via metabolic abnormalities.

Polar vacuolar distribution is essential for accurate asymmetric division of Arabidopsis zygotes.

In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is polarized, possessing the nucleus at the apical tip and large vacuoles at the basal end. Despite their known polar localization, whether the positioning of the vacuoles and the nucleus is coordinated and what the role of the vacuole is in the asymmetric zygotic division remain elusive. In the present study, we utilized a live-cell imaging system to visualize the dynamics of vacuoles during the entire process of zygote polarization in Arabidopsis Image analysis revealed that the vacuoles formed tubular strands around the apically migrating nucleus. They gradually accumulated at the basal region and filled the space, resulting in asymmetric distribution in the mature zygote. To assess the role of vacuoles in the zygote, we screened various vacuole mutants and identified that shoot gravitropism2 (sgr2), in which the vacuolar structural change was impaired, failed to form tubular vacuoles and to polarly distribute the vacuole. In sgr2, large vacuoles occupied the apical tip and thus nuclear migration was blocked, resulting in a more symmetric zygotic division. We further observed that tubular vacuole formation and asymmetric vacuolar distribution both depended on the longitudinal array of actin filaments. Overall, our results show that vacuolar dynamics is crucial not only for the polar distribution along actin filaments but also for adequate nuclear positioning, and consequently zygote-division asymmetry.

Lateral Inhibition by a Peptide Hormone-Receptor Cascade during Arabidopsis Lateral Root Founder Cell Formation.

In plants, the position of lateral roots (LRs) depends on initiation sites induced by auxin. The domain of high auxin response responsible for LR initiation stretches over several cells, but only a pair of pericycle cells (LR founder cells) will develop into LRs. In this work, we identified a signaling cascade controlling LR formation through lateral inhibition. It comprises a peptide hormone TARGET OF LBD SIXTEEN 2 (TOLS2), its receptor RLK7, and a downstream transcription factor PUCHI. TOLS2 is expressed at the LR founder cells and inhibits LR initiation. Time-lapse imaging of auxin-responsive DR5:LUCIFERASE reporter expression revealed that occasionally two pairs of LR founder cells are specified in close proximity even in wild-type and that one of them exists only transiently and disappears in an RLK7-dependent manner. We propose that the selection of LR founder cells by the peptide hormone-receptor cascade ensures proper LR spacing.

ERECTA-family genes coordinate stem cell functions between the epidermal and internal layers of the shoot apical meristem.

The epidermal cell layer and the tissues that lie underneath have different intrinsic functions during plant development. The stem cells within the shoot apical meristem (SAM) that give rise to aerial structures are located in the epidermal and internal tissue layers. However, our understanding of how the functions of these stem cells are coordinated across tissue layers so stem cells can behave as a single population remains limited. WUSCHEL (WUS) functions as a master regulator of stem cell activity. Here, we show that loss of function in the ERECTA (ER)-family receptor kinase genes can rescue the mutant phenotype of wus plants (loss of stem cells), as demonstrated by the reinstated expression of a stem cell marker gene in the SAM epidermis. Localized ER expression in the epidermis can suppress the SAM phenotype caused by loss of ER-family activity. Furthermore, the CLAVATA3- and cytokinin-induced outputs, which contribute to stem cell homeostasis, are dysfunctional in a tissue layer-specific manner in ER-family mutants. Collectively, our findings suggest that the ER family plays a role in the coordination of stem cell behavior between different SAM tissue layers.

The Arabidopsis LAZY1 Family Plays a Key Role in Gravity Signaling within Statocytes and in Branch Angle Control of Roots and Shoots.

During gravitropism, the directional signal of gravity is perceived by gravity-sensing cells called statocytes, leading to asymmetric distribution of auxin in the responding organs. To identify the genes involved in gravity signaling in statocytes, we performed transcriptome analyses of statocyte-deficient Arabidopsis thaliana mutants and found two candidates from the LAZY1 family, AtLAZY1/LAZY1-LIKE1 (LZY1) and AtDRO3/AtNGR1/LZY2 We showed that LZY1, LZY2, and a paralog AtDRO1/AtNGR2/LZY3 are redundantly involved in gravitropism of the inflorescence stem, hypocotyl, and root. Mutations of LZY genes affected early processes in gravity signal transduction without affecting amyloplast sedimentation. Statocyte-specific expression of LZY genes rescued the mutant phenotype, suggesting that LZY genes mediate gravity signaling in statocytes downstream of amyloplast displacement, leading to the generation of asymmetric auxin distribution in gravity-responding organs. We also found that lzy mutations reversed the growth angle of lateral branches and roots. Moreover, expression of the conserved C-terminal region of LZY proteins also reversed the growth direction of primary roots in the lzy mutant background. In lateral root tips of lzy multiple mutants, asymmetric distribution of PIN3 and auxin response were reversed, suggesting that LZY genes regulate the direction of polar auxin transport in response to gravity through the control of asymmetric PIN3 expression in the root cap columella.

ERECTA-family receptor kinase genes redundantly prevent premature progression of secondary growth in the Arabidopsis hypocotyl.

Secondary growth is driven by continuous cell proliferation and differentiation of the cambium that acts as vascular stem cells, producing xylem and phloem to expand vascular tissues laterally. During secondary growth of hypocotyls in Arabidopsis thaliana, the xylem undergoes a drastic phase transition from a parenchyma-producing phase to a fiber-producing phase at the appropriate time. However, it remains to be fully elucidated how progression of secondary growth is properly controlled. We focused on phenotypes of hypocotyl vasculatures caused by double mutation in ERECTA (ER) and ER-LIKE1 (ERL1) receptor-kinase genes to elucidate their roles in secondary growth. ER and ERL1 redundantly suppressed excessive radial growth of the hypocotyl vasculature during secondary growth. ER and ERL1 also prevented premature initiation of the fiber differentiation process mediated by the NAC SECONDARY WALL THICKENING PROMOTING FACTORs in the hypocotyl xylem. Upon floral transition, the hypocotyl xylem gained a competency to respond to GA in a BREVIPEDICELLUS-dependent manner, which was a prerequisite for fiber differentiation. However, even after the floral transition, ER and ERL1 prevented precocious initiation of the GA-mediated fiber formation. Collectively, our findings reveal that ER and ERL1 redundantly prevent premature progression of sequential events in secondary growth.

Impact of erecta mutation on leaf serration differs between Arabidopsis accessions.

Serrations or teeth of plant leaves are a morphological trait regulated genetically and environmentally. Very recently, it has been reported that the receptor kinases encoded by three ERECTA (ER)-family genes, ER, ER-LIKE1 (ERL1) and ERL2, redundantly play a role in tooth growth in Arabidopsis thaliana. In the report, Columbia (Col) accession was used for analyses, where none of the signal mutant of the ER-family genes exhibited serration defects. The toothless, smooth leaf margin phenotype was evident only when two out of the three ER-family genes were lost. Interestingly, it has been widely recognized that the Arabidopsis accession Landsberg erecta (L.er), which carries a loss-of-function mutation in ER, develops round leaves with smaller leaf teeth. Here, we show that the functional ER transgene promotes the tooth growth in L.er to the level of Col, indicating that the er mutation in L.er is likely responsible for the reduced growth of leaf teeth. This suggests that er single mutation affects tooth growth in a different manner between Col and L.er backgrounds, though the molecular basis for this background-dependent effect remains to be addressed.

Isolation of New Gravitropic Mutants under Hypergravity Conditions.

Forward genetics is a powerful approach used to link genotypes and phenotypes, and mutant screening/analysis has provided deep insights into many aspects of plant physiology. Gravitropism is a tropistic response in plants, in which hypocotyls and stems sense the direction of gravity and grow upward. Previous studies of gravitropic mutants have suggested that shoot endodermal cells in Arabidopsis stems and hypocotyls are capable of sensing gravity (i.e., statocytes). In the present study, we report a new screening system using hypergravity conditions to isolate enhancers of gravitropism mutants, and we also describe a rapid and efficient genome mapping method, using next-generation sequencing (NGS) and single nucleotide polymorphism (SNP)-based markers. Using the endodermal-amyloplast less 1 (eal1) mutant, which exhibits defective development of endodermal cells and gravitropism, we found that hypergravity (10 g) restored the reduced gravity responsiveness in eal1 hypocotyls and could, therefore, be used to obtain mutants with further reduction in gravitropism in the eal1 background. Using the new screening system, we successfully isolated six ene (enhancer of eal1) mutants that exhibited little or no gravitropism under hypergravity conditions, and using NGS and map-based cloning with SNP markers, we narrowed down the potential causative genes, which revealed a new genetic network for shoot gravitropism in Arabidopsis.

A Secreted Peptide and Its Receptors Shape the Auxin Response Pattern and Leaf Margin Morphogenesis.

Secreted peptides mediate intercellular communication [1, 2]. Several secreted peptides in the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family regulate morphogenesis of tissues, such as stomata and inflorescences in plants [3-15]. The biological functions of other EPFL family members remain unknown. Here, we show that the EPFL2 gene is required for growth of leaf teeth. EPFL2 peptide physically interacts with ERECTA (ER) family receptor-kinases and, accordingly, the attenuation of ER family activities leads to formation of toothless leaves. During the tooth growth process, responses to the phytohormone auxin are maintained at tips of the teeth to promote their growth [16-19]. In the growing tooth tip of epfl2 and multiple er family mutants, the auxin response becomes broader. Conversely, overexpression of EPFL2 diminishes the auxin response, indicating that the EPFL2 signal restricts the auxin response to the tooth tip. Interestingly, the tip-specific auxin response in turn organizes characteristic expression patterns of ER family and EPFL2 by enhancing ER family expression at the tip while eliminating the EPFL2 expression from the tip. Our findings identify the novel ligand-receptor pairs promoting the tooth growth, and further reveal a feedback circuit between the peptide-receptor system and auxin response as a mechanism for maintaining proper auxin maxima during leaf margin morphogenesis.

Auxin-dependent compositional change in Mediator in ARF7- and ARF19-mediated transcription.

Mediator is a multiprotein complex that integrates the signals from transcription factors binding to the promoter and transmits them to achieve gene transcription. The subunits of Mediator complex reside in four modules: the head, middle, tail, and dissociable CDK8 kinase module (CKM). The head, middle, and tail modules form the core Mediator complex, and the association of CKM can modify the function of Mediator in transcription. Here, we show genetic and biochemical evidence that CKM-associated Mediator transmits auxin-dependent transcriptional repression in lateral root (LR) formation. The AUXIN/INDOLE 3-ACETIC ACID 14 (Aux/IAA14) transcriptional repressor inhibits the transcriptional activity of its binding partners AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 by making a complex with the CKM-associated Mediator. In addition, TOPLESS (TPL), a transcriptional corepressor, forms a bridge between IAA14 and the CKM component MED13 through the physical interaction. ChIP assays show that auxin induces the dissociation of MED13 but not the tail module component MED25 from the ARF7 binding region upstream of its target gene. These findings indicate that auxin-induced degradation of IAA14 changes the module composition of Mediator interacting with ARF7 and ARF19 in the upstream region of their target genes involved in LR formation. We suggest that this regulation leads to a quick switch of signal transmission from ARFs to target gene expression in response to auxin.

Efficient In Planta Detection and Dissection of De Novo Mutation Events in the Arabidopsis thaliana Disease Resistance Gene UNI.

Plants possess disease resistance (R) proteins encoded by R genes, and each R protein recognizes a specific pathogen factor(s) for immunity. Interestingly, a remarkably high degree of polymorphisms in R genes, which are traces of past mutation events during evolution, suggest the rapid diversification of R genes. However, little is known about molecular aspects that facilitate the rapid change of R genes because of the lack of tools that enable us to monitor de novo R gene mutations efficiently in an experimentally feasible time scale, especially in living plants. Here we introduce a model assay system that enables efficient in planta detection of de novo mutation events in the Arabidopsis thaliana R gene UNI in one generation. The uni-1D mutant harbors a gain-of-function allele of the UNI gene. uni-1D heterozygous individuals originally exhibit dwarfism with abnormally short stems. However, interestingly, morphologically normal stems sometimes emerge spontaneously from the uni-1D plants, and the morphologically reverted tissues carry additional de novo mutations in the UNI gene. Strikingly, under an extreme condition, almost half of the examined population shows the reversion phenomenon. By taking advantage of this phenomenon, we demonstrate that the reversion frequency is remarkably sensitive to a variety of fluctuations in DNA stability, underlying a mutable tendency of the UNI gene. We also reveal that activities of the salicylic acid pathway and DNA damage sensor pathway are involved in the reversion phenomenon. Thus, we provide an experimentally feasible model tool to explore factors and conditions that significantly affect the R gene mutation phenomenon.

An ABC transporter B family protein, ABCB19, is required for cytoplasmic streaming and gravitropism of the inflorescence stems.

A significant feature of plant cells is the extensive motility of organelles and the cytosol, which was originally defined as cytoplasmic streaming. We suggested previously that a three-way interaction between plant-specific motor proteins myosin XIs, actin filaments, and the endoplasmic reticulum (ER) was responsible for cytoplasmic streaming. (1) Currently, however, there are no reports of molecular components for cytoplasmic streaming other than the actin-myosin-cytoskeleton and ER-related proteins. In the present study, we found that elongated cells of inflorescence stems of Arabidopsis thaliana exhibit vigorous cytoplasmic streaming. Statistical analysis showed that the maximal velocity of plastid movements is 7.26 µm/s, which is much faster than the previously reported velocities of organelles. Surprisingly, the maximal velocity of streaming in the inflorescence stem cells was significantly reduced to 1.11 µm/s in an Arabidopsis mutant, abcb19-101, which lacks ATP BINDING CASSETTE SUBFAMILY B19 (ABCB19) that mediates the polar transport of the phytohormone auxin together with PIN-FORMED (PIN) proteins. Polar auxin transport establishes the auxin concentration gradient essential for plant development and tropisms. Deficiency of ABCB19 activity eventually caused enhanced gravitropic responses of the inflorescence stems and abnormally flexed inflorescence stems. These results suggest that ABCB19-mediated auxin transport plays a role not only in tropism regulation, but also in cytoplasmic streaming.

Transcriptional regulation of PIN genes by FOUR LIPS and MYB88 during Arabidopsis root gravitropism.

PIN proteins are auxin export carriers that direct intercellular auxin flow and in turn regulate many aspects of plant growth and development including responses to environmental changes. The Arabidopsis R2R3-MYB transcription factor FOUR LIPS (FLP) and its paralogue MYB88 regulate terminal divisions during stomatal development, as well as female reproductive development and stress responses. Here we show that FLP and MYB88 act redundantly but differentially in regulating the transcription of PIN3 and PIN7 in gravity-sensing cells of primary and lateral roots. On the one hand, FLP is involved in responses to gravity stimulation in primary roots, whereas on the other, FLP and MYB88 function complementarily in establishing the gravitropic set-point angles of lateral roots. Our results support a model in which FLP and MYB88 expression specifically determines the temporal-spatial patterns of PIN3 and PIN7 transcription that are closely associated with their preferential functions during root responses to gravity.

Live cell imaging of cytoskeletal and organelle dynamics in gravity-sensing cells in plant gravitropism.

Plants sense gravity and change their morphology/growth direction accordingly (gravitropism). The early process of gravitropism, gravity sensing, is supposed to be triggered by sedimentation of starch-filled plastids (amyloplasts) in statocytes such as root columella cells and shoot endodermal cells. For several decades, many scientists have focused on characterizing the role of the amyloplasts and observed their intracellular sedimentation in various plants. Recently, it has been discovered that the complex sedimentary movements of the amyloplasts are created not only by gravity but also by cytoskeletal/organelle dynamics, such as those of actin filaments and the vacuolar membrane. Thus, to understand how plants sense gravity, we need to analyze both amyloplast movements and their regulatory systems in statocytes. We have developed a vertical-stage confocal microscope that allows multicolor fluorescence imaging of amyloplasts, actin filaments and vacuolar membranes in vertically oriented plant tissues. We also developed a centrifuge microscope that allows bright-field imaging of amyloplasts during centrifugation. These microscope systems provide new insights into gravity-sensing mechanisms in Arabidopsis.

Regulation of organ straightening and plant posture by an actin-myosin XI cytoskeleton.

Plants are able to bend nearly every organ in response to environmental stimuli such as gravity and light(1,2). After this first phase, the responses to stimuli are restrained by an independent mechanism, or even reversed, so that the organ will stop bending and attain its desired posture. This phenomenon of organ straightening has been called autotropism(3) and autostraightening(4) and modelled as proprioception(5). However, the machinery that drives organ straightening and where it occurs are mostly unknown. Here, we show that the straightening of inflorescence stems is regulated by an actin-myosin XI cytoskeleton in specialized immature fibre cells that are parallel to the stem and encircle it in a thin band. Arabidopsis mutants defective in myosin XI (specifically XIf and XIk) or ACTIN8 exhibit hyperbending of stems in response to gravity, an effect independent of the physical properties of the shoots. The actin-myosin XI cytoskeleton enables organs to attain their new position more rapidly than would an oscillating series of diminishing overshoots in environmental stimuli. We propose that the long actin filaments in elongating fibre cells act as a bending tensile sensor to perceive the organ's posture and trigger the straightening system.

The CUC1 and CUC2 genes promote carpel margin meristem formation during Arabidopsis gynoecium development.

Carpel margin meristems (CMMs), a pair of meristematic tissues present along the margins of two fused carpel primordia of Arabidopsis thaliana, are essential for the formation of ovules and the septum, two major internal structures of the gynoecium. Although a number of regulatory factors involved in shoot meristem activity are known to be required for the formation of these gynoecial structures, their direct roles in CMM development have yet to be addressed. Here we show that the CUP-SHAPED COTYLEDON genes CUC1 and CUC2, which are essential for shoot meristem initiation, are also required for formation and stable positioning of the CMMs. Early in CMM formation, CUC1 and CUC2 are also required for expression of the SHOOT MERISTEMLESS gene, a central regulator for stem cell maintenance in the shoot meristem. Moreover, plants carrying miR164-resistant forms of CUC1 and CUC2 resulted in extra CMM activity with altered positioning. Our results thus demonstrate that the two regulatory proteins controlling shoot meristem activity also play critical roles in elaboration of the female reproductive organ through the control of meristematic activity.

A unique HEAT repeat-containing protein SHOOT GRAVITROPISM6 is involved in vacuolar membrane dynamics in gravity-sensing cells of Arabidopsis inflorescence stem.

Plant vacuoles play critical roles in development, growth and stress responses. In mature cells, vacuolar membranes (VMs) display several types of structures, which are formed by invagination and folding of VMs into the lumenal side and can gradually move and change shape. Although such VM structures are observed in a broad range of tissue types and plant species, the molecular mechanism underlying their formation and maintenance remains unclear. Here, we report that a novel HEAT-repeat protein, SHOOT GRAVITROPISM6 (SGR6), of Arabidopsis is involved in the control of morphological changes and dynamics of VM structures in endodermal cells, which are the gravity-sensing cells in shoots. SGR6 is a membrane-associated protein that is mainly localized to the VM in stem endodermal cells. The sgr6 mutant stem exhibits a reduced gravitropic response. Higher plants utilize amyloplast sedimentation as a means to sense gravity direction. Amyloplasts are surrounded by VMs in Arabidopsis endodermal cells, and the flexible and dynamic structure of VMs is important for amyloplast sedimentation. We demonstrated that such dynamic features of VMs are gradually lost in sgr6 endodermal cells during a 30 min observation period. Histological analysis revealed that amyloplast sedimentation was impaired in sgr6. Detailed live-cell imaging analyses revealed that the VM structures in sgr6 had severe defects in morphological changes and dynamics. Our results suggest that SGR6 is a novel protein involved in the formation and/or maintenance of invaginated VM structures in gravity-sensing cells.