The emerging roles of clathrin-mediated endocytosis in plant development and stress responses.

Clathrin-mediated endocytosis (CME) is a highly conserved pathway that plays a crucial role in the endocytosis of plasma membrane proteins in eukaryotic cells. The pathway is initiated when the adaptor protein complex 2 (AP2) and TPLATE complex (TPC) work together to recognize cargo proteins and recruit clathrin. This review provides a concise overview of the functions of each subunit of AP2 and TPC, and highlights the involvement of CME in various biological processes, such as pollen development, root development, nutrient transport, extracellular signal transduction, auxin polar transport, hyperosmotic stress, salinity stress, high ammonium stress, and disease resistance. Additionally, the review explores the regulation of CME by phytohormones, clathrin-mediated exocytosis (CMX), and AP2M phosphorylation. It also suggests potential future research directions for CME.

Ethylene insensitive 2 (EIN2) destiny shaper: The post-translational modification.

PTMs (Post-Translational Modifications) of proteins facilitate rapid modulation of protein function in response to various environmental stimuli. The EIN2 (Ethylene Insensitive 2) protein is a core regulatory of the ethylene signaling pathway. Recent findings have demonstrated that PTMs, including protein phosphorylation, ubiquitination, and glycosylation, govern EIN2 trafficking, subcellular localization, stability, and physiological roles. The cognition of multiple PTMs in EIN2 underscores the stringent regulation of protein. Consequently, a thorough review of the regulatory role of PTMs in EIN2 functions will improve our profound comprehension of the regulation mechanism and various physiological processes of EIN2-mediated signaling pathways. This review discusses the evolution, functions, structure and characteristics of EIN2 protein in plants. Additionally, this review sheds light on the progress of protein ubiquitination, phosphorylation, O-Glycosylation in the regulation of EIN2 functions, and the unresolved questions and future perspectives.

FOUR LIPS plays a role in meristemoid-to-GMC fate transition during stomatal development in Arabidopsis.

Meristemoids, which are stomatal precursor cells, exhibit self-renewal and differentiation abilities. However, the only known core factor associated with meristemoid division termination and fate transition is the heterodimer formed by the basic helix-loop-helix proteins MUTE and SCREAMs (SCRMs). FOUR LIPS (FLP), a well-known transcription factor that restricts guard mother cell (GMC) division, is a direct target of MUTE. Whether FLP involves in meristemoid differentiation is unknown. Through sensitized genetic screening of flp-1, we identified a mute-like (mutl) mutant with arrested meristemoids. The mutant carried a novel allele of the MUTE locus, i.e., mute-4. Intriguingly, mute-4 is a hypomorphic allele that exhibits wild-type appearance with slightly delayed meristemoid-to-GMC transition, whereas it renders an unexpected mutl epidermis with most meristemoids arrested and very few stomata when combined with flp (flp mute-4), suggesting that FLP is a positive regulator during this transition process. Consistently, the expression of FLP increased during GMC commitment, and the number of cells at this stage was markedly increased in flp. flp scrm double mutants produced arrested meristemoids similar to mute, and FLP was able to interact physically with SCRM. Taken together, our results demonstrate that FLP functions together with MUTE and SCRMs to direct meristemoid-to-GMC fate transition.

The EPFL-ERf-SERK signaling controls integument development in Arabidopsis.

As the seed precursor, the ovule produces the female gametophyte (or embryo sac), and the subsequent double fertilization occurs in it. The integuments emerge sequentially from the integument primordia at the early stages of ovule development and finally enwrap the embryo sac gradually during gametogenesis, protecting and nursing the embryo sac. However, the mechanisms regulating integument development are still obscure. In this study, we show that SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASES (SERKs) play essential roles during integument development in Arabidopsis thaliana. The serk1/2/3 triple mutant shows arrested integuments and abnormal embryo sacs, similar defects also found in the triple loss-of-function mutants of ERECTA family (ERf) genes. Ovules of serk1/2/3 er erl1/2 show defects similar to er erl1/2 and serk1/2/3. Results of yeast two-hybrid analyses, bimolecular fluorescence complementation (BiFC) analyses, and co-immunoprecipitation assays demonstrated that SERKs interact with ERf, which depends on EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family small peptides. The sextuple mutant epfl1/2/3/4/5/6 shows integument defects similar to both of er erl1/2 and serk1/2/3. Our results demonstrate that ERf-SERK-mediated EPFL signaling orchestrates the development of the female gametophyte and the surrounding sporophytic integuments.

Rice protein phosphatase 1 regulatory subunits OsINH2 and OsINH3 participate actively in growth and adaptive responses under abscisic acid.

Rice (Oryza sativa L.), a worldwide staple food crop, is affected by various environmental stressors that ultimately reduce yield. However, diversified physiological and molecular responses enable it to cope with adverse factors. It includes the integration of numerous signaling in which protein phosphatase 1 (PP1) plays a pivotal role. Research on PP1 has been mostly limited to the PP1 catalytic subunit in numerous cellular progressions. Therefore, we focused on the role of PP1 regulatory subunits (PP1r), OsINH2 and OsINH3, homologs of AtINH2 and AtINH3 in Arabidopsis, in rice growth and stress adaptations. Our observations revealed that these are ubiquitously expressed regulatory subunits that interacted and colocalized with their counter partners, type 1 protein phosphatase (OsTOPPs) but could not change their subcellular localization. The mutation in OsINH2 and OsINH3 reduced pollen viability, thereby affected rice fertility. They were involved in abscisic acid (ABA)-mediated inhibition of seed germination, perhaps by interacting with osmotic stress/ABA-activated protein kinases (OsSAPKs). Meanwhile, they positively participated in osmotic adjustment by proline biosynthesis, detoxifying reactive oxygen species (ROS) through peroxidases (POD), reducing malondialdehyde formation (MDA), and regulating stress-responsive genes. Moreover, their co-interaction proposed they might mediate cellular processes together or by co-regulation; however, the special behavior of two different PP1r is needed to explore. In a nutshell, this research enlightened the involvement of OsINH2 and OsINH3 in the reproductive growth of rice and adaptive strategies under stress. Hence, their genetic interaction with ABA components and deep mechanisms underlying osmotic regulation and ROS adjustment would explain their role in complex signaling. This research offers the basis for introducing stress-resistant crops.

Type one protein phosphatase regulates fixed-carbon starvation-induced autophagy in Arabidopsis.

Autophagy, a conserved pathway that carries out the bulk degradation of cytoplasmic material in eukaryotic cells, is critical for plant physiology and development. This process is tightly regulated by ATG13, a core component of the ATG1 kinase complex, which initiates autophagy. Although ATG13 is known to be dephosphorylated immediately after nutrient starvation, the phosphatase regulating this process is poorly understood. Here, we determined that the Arabidopsis (Arabidopsis thaliana) septuple mutant (topp-7m) and octuple mutant (topp-8m) of TYPE ONE PROTEIN PHOSPHATASE (TOPP) exhibited significantly reduced tolerance to fixed-carbon (C) starvation due to compromised autophagy activity. Genetic analysis placed TOPP upstream of autophagy. Interestingly, ATG13a was found to be an interactor of TOPP. TOPP directly dephosphorylated ATG13a in vitro and in vivo. We identified 18 phosphorylation sites in ATG13a by LC-MS. Phospho-dead ATG13a at these 18 sites significantly promoted autophagy and increased the tolerance of the atg13ab mutant to fixed-C starvation. The dephosphorylation of ATG13a facilitated ATG1a-ATG13a complex formation. Consistently, the recruitment of ATG13a for ATG1a was markedly inhibited in topp-7m-1. Finally, TOPP-controlled dephosphorylation of ATG13a boosted ATG1a phosphorylation. Taken together, our study reveals the crucial role of TOPP in regulating autophagy by stimulating the formation of the ATG1a-ATG13a complex by dephosphorylating ATG13a in Arabidopsis.

The emerging roles of ATG1/ATG13 kinase complex in plants.

Autophagy is a conserved system from yeast to mammals that mediates the degradation and renovation of cellular components. This process is mainly driven by numerous autophagy-related (ATG) proteins. Among these components, the ATG1/ATG13 complex plays an essential role in initiating autophagy, sensing nutritional status signals, recruiting downstream ATG proteins to the autophagosome formation site, and governing autophagosome formation. In this review, we will focus on the ATG1/ATG13 kinase complex, summarizing and discussing the current views on the composition, structure, function, and regulation of this complex in plants.

RNA polymerase II associated proteins regulate stomatal development through direct interaction with stomatal transcription factors in Arabidopsis thaliana.

RNA polymerase II (Pol II) associated proteins (RPAPs) have been ascribed diverse functions at the cellular level; however, their roles in developmental processes in yeasts, animals and plants are very poorly understood. Through screening for interactors of NRPB3, which encodes the third largest subunit of Pol II, we identified RIMA, the orthologue of mammalian RPAP2. A combination of genetic and biochemical assays revealed the role of RIMA and other RPAPs in stomatal development in Arabidopsis thaliana. We show that RIMA is involved in nuclear import of NRPB3 and other Pol II subunits, and is essential for restraining division and for establishing cell identity in the stomatal cell lineage. Moreover, plant RPAPs IYO/RPAP1 and QQT1/RPAP4, which interact with RIMA, are also crucial for stomatal development. Importantly, RIMA and QQT1 bind physically to stomatal transcription factors SPEECHLESS, MUTE, FAMA and SCREAMs. The RIMA-QQT1-IYO complex could work together with key stomatal transcription factors and Pol II to drive cell fate transitions in the stomatal cell lineage. Direct interactions with stomatal transcription factors provide a novel mechanism by which RPAP proteins may control differentiation of cell types and tissues in eukaryotes.

RSD1 Is Essential for Stomatal Patterning and Files in Rice.

Stomatal density is an important factor that determines the efficiency of plant gas exchange and water transpiration. Through forward genetics, we screened a mutant rice stomata developmental defect 1 (rsd1-1) with decreased stomatal density and clustered stomata in rice (Oryza sativa). After the first asymmetric division, some of the larger sister cells undergo an extra asymmetric division to produce a small cell neighboring guard mother cell. Some of these small cells develop into stomata, which leads to stomatal clustering, and the rest arrested or developed into pavement cell. After map-based cloning, we found the protein encoded by this gene containing DUF630 and DUF632 domains. Evolutionary analysis showed that the DUF630/632 gene family differentiated earlier in land plants. It was found that the deletion of RSD1 would lead to the disorder of gene expression regarding stomatal development, especially the expression of stomatal density and distribution 1 (OsSDD1). Through the construction of OsSDD1 deletion mutants by CRISPR-Cas9, we found that, similar to rsd1 mutants, the ossdd1 mutants have clustered stomata and extra small cells adjacent to the stomata. OsSDD1 and RSD1 are both required for inhibiting ectopic asymmetric cell divisions (ACDs) and clustered stomata. By dehydration stress assay, the decreased stomatal density of rsd1 mutants enhanced their dehydration avoidance. This study characterized the functions of RSD1 and OsSDD1 in rice stomatal development. Our findings will be helpful in developing drought-resistant crops through controlling the stomatal density.

Role of Protein Phosphatase1 Regulatory Subunit3 in Mediating the Abscisic Acid Response.

Protein phosphatase1 (PP1) plays important roles in eukaryotes, including in plant hormone responses, and functions as a holoenzyme that consists of catalytic and regulatory subunits. Animal genomes encode ∼200 PP1-interacting proteins; by contrast, only a few have been reported in plants. In this study, PP1 Regulatory Subunit3 (PP1R3), a protein that interacts with PP1 in Arabidopsis (Arabidopsis thaliana), was characterized by mass spectrometry. PP1R3 was widely expressed in various plant tissues and PP1R3 colocalized with Type One Protein Phosphatases (TOPPs) in the nucleus and cytoplasm. The pp1r3 mutants were hypersensitive to abscisic acid (ABA), similar to the dominant-negative mutant topp4-1 or the loss-of-function multiple mutants topp1 topp4-3, topp8 topp9, topp6/7/9, topp1/2/4-3/6/7/9, and topp1/4-3/5/6/7/8/9 (topp-7m). About two-thirds of differentially expressed genes in topp-7m showed the same gene expression changes as in pp1r3-2 In response to ABA, the phenotypes of pp1r3 topp1 topp4-3 and pp1r3 topp4-1 were consistent with those of pp1r3, while pp1r3 abi1-1 showed an additive effect of the pp1r3 and abi1-1 (mutation in Abscisic Acid Insensitive1 [ABI1]) single mutants. Moreover, pp1r3 could partially recover the ABA response-related phenotype, gene expression, and plant morphology of topp4-1 PP1R3 inhibited TOPP enzyme activity and facilitated the nuclear localization of TOPP4. By contrast, ABA treatment increased the amounts of TOPP1 and TOPP4 in the cytoplasm. Importantly, nuclear localization of TOPP4 partially restored the ABA-hypersensitive phenotype of topp4-1 Overall, our results suggest that the PP1R3:TOPP holoenzyme functions in parallel with ABI1 in the nucleus to regulate ABA signaling.

SPEECHLESS Speaks Loudly in Stomatal Development.

Stomata, the small pores on the epidermis of plant shoot, control gas exchange between the plant and environment and play key roles in plant physiology, evolution, and global ecology. Stomatal development is initiated by the basic helix-loop-helix (bHLH) transcription factor SPEECHLESS (SPCH), whose central importance in stomatal development has recently come to light. SPCH integrates intralineage signals and serves as an acceptor of hormonal and environmental signals to regulate stomatal density and patterning during the development. SPCH also plays a direct role in regulating asymmetric cell division in the stomatal lineage. Owing to its importance in stomatal development, SPCH expression is tightly and spatiotemporally regulated. The purpose of this review is to provide an overview of the SPCH-mediated regulation of stomatal development, reinforcing the idea that SPCH is the central molecular hub for stomatal development.

Type one protein phosphatases (TOPPs) contribute to the plant defense response in Arabidopsis.

Plant immunity must be tightly controlled to avoid activation of defense mechanisms in the absence of pathogen attack. Protein phosphorylation is a common mechanism regulating immune signaling. In Arabidopsis thaliana, nine members of the type one protein phosphatase (TOPP) family (also known as protein phosphatase 1, PP1) have been identified. Here, we characterized the autoimmune phenotype of topp4-1, a previously identified dominant-negative mutant of TOPP4. Epistasis analysis showed that defense activation in topp4-1 depended on NON-RACE-SPECIFIC DISEASE RESISTANCE1, PHYTOALEXIN DEFICIENT4, and the salicylic acid pathway. We generated topp1/4/5/6/7/8/9 septuple mutants to investigate the function of TOPPs in plant immunity. Elevated defense gene expression and enhanced resistance to Pseudomonas syringae pv. tomato (Pst) DC3000 in the septuple mutant indicate that TOPPs function in plant defense responses. Furthermore, TOPPs physically interacted with mitogen-activated protein kinases (MAPKs) and affected the MAPK-mediated downstream defense pathway. Thus, our study reveals that TOPPs are important regulators of plant immunity.

An unreported NB-LRR protein SUT1 is required for the autoimmune response mediated by type one protein phosphatase 4 mutation (topp4-1) in Arabidopsis.

Our previous study indicates that protein phosphatase 1 (PP1) is involved in plant immunity. To elucidate the underlying molecular mechanism, a genetic screening assay was carried out to identify suppressors of type one protein phosphatase 4 mutation (topp4-1) (sut). Molecular and genetic approaches were used to investigate the mechanism of activation of autoimmune response in topp4-1. We performed a map-based cloning assay to identify the SUT1 gene, which encodes a coiled-coil nucleotide-binding leucine-rich-repeat (NB-LRR) protein (CNL). SUT1 physically interacts with TYPE ONE PROTEIN PHOSPHATASE 4 (TOPP4) and topp4-1. The mutated topp4-1 protein activates the autoimmune response in the cytoplasm and promotes the accumulation of SUT1 at both the transcription and the protein levels. Furthermore, our genetic and physical interactions confirm that the topp4-1-induced autoimmune responses are probably mediated by HEAT SHOCK PROTEIN 90 (HSP90) and REQUIRED FOR MLA12 RESISTANCE 1 (RAR1). This study reveals that TOPP4 phosphatase is likely guarded by SUT1 in plant immunity.

SERK Receptor-like Kinases Control Division Patterns of Vascular Precursors and Ground Tissue Stem Cells during Embryo Development in Arabidopsis.

During embryo development, the vascular precursors and ground tissue stem cells divide to renew themselves and produce the vascular tissue, endodermal cells, and cortical cells. However, the molecular mechanisms regulating division of these stem cells have remained largely elusive. In this study, we show that loss of function of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) genes results in aberrant embryo development. Fewer cortical, endodermal, and vascular cells are generated in the embryos of serk1 serk2 bak1 triple mutants. WUSCHEL-RELATED HOMEOBOX 5 (WOX5) is ectopically expressed in vascular cells of serk1 serk2 bak1 embryos. The first transverse division of vascular precursors in mid-globular embryos and second asymmetric division of ground tissue stem cells in early-heart embryos are abnormally altered to a longitudinal division. The embryo defects can be partially rescued by constitutively activated mitogen-activated protein kinase (MAPK) kinase kinase YODA (YDA) and MAPK kinase MKK5. Taken together, our results reveal that SERK-mediated signals regulate division patterns of vascular precursors and ground tissue stem cells, likely via the YDA-MKK4/5 cascade, during embryo development.

Multiple transcriptional factors control stomata development in rice.

Grass stomata can balance gas exchange and evaporation effectively in rapidly changing environments via their unique anatomical features. Although the key components of stomatal development in Arabidopsis have been largely elucidated over the past decade, the molecular mechanisms that govern stomatal development in grasses are poorly understood. Via the genome editing system and T-DNA insertion lines, the key transcriptional factors (TFs) regulating stomatal development in rice (Oryza sativa) were knocked out. A combination of genetic and biochemical assays subsequently revealed the functions of these TFs. OsSPCH/OsICE is essential for the initiation of stomatal lineage. OsMUTE/OsICE determines meristemoid to guard mother cell (GMC) transition. OsFAMA/OsICE influences subsidiary mother cell asymmetric division and mature stoma differentiation. OsFLP regulates the orientation of GMC symmetrical division. More importantly, we found that OsSCR/OsSHR controls the initiation of stomatal lineage cells and the formation of subsidiary cells. The transcription of OsSCR is activated by OsSPCH and OsMUTE. This study characterised the functions of master regulatory TFs that control each stomatal developmental stage in rice. Our findings are helpful for elucidating how various species reprogramme the molecular mechanisms to generate different stomatal types during evolution.

CIK Receptor Kinases Determine Cell Fate Specification during Early Anther Development in Arabidopsis.

Appropriate cell division and differentiation ensure normal anther development in angiosperms. BARELY ANY MERISTEM 1/2 (BAM1/2) and RECEPTOR-LIKE PROTEIN KINASE2 (RPK2), two groups of leucine-rich repeat receptor-like protein kinases, are required for early anther cell specification. However, little is known about the molecular mechanisms underlying these two RLK-mediated signaling pathways. Here, we show that CLAVATA3 INSENSITIVE RECEPTOR KINASEs (CIKs), a group of novel coreceptor protein kinase-controlling stem cell homeostasis, play essential roles in BAM1/2- and RPK2-regulated early anther development in Arabidopsis thaliana The archesporial cells of cik1/2/3 triple and cik1/2/3/4 quadruple mutant anthers perform anticlinal division instead of periclinal division. Defective cell division and specification of the primary and inner secondary parietal cells occur in these mutant anthers. The disordered divisions and specifications of anther wall cells finally result in excess microsporocytes and a lack of one to three parietal cell layers in mutant anthers, resembling rpk2 or bam1/2 mutant anthers. Genetic and biochemical analyses indicate that CIKs function as coreceptors of BAM1/2 and RPK2 to regulate archesporial cell division and determine the specification of anther parietal cells.

A group of receptor kinases are essential for CLAVATA signalling to maintain stem cell homeostasis.

Continuous organ initiation and outgrowth in plants relies on the proliferation and differentiation of stem cells maintained by the CLAVATA (CLV)-WUSCHEL (WUS) negative-feedback loop1-3. Leucine-rich repeat receptor-like protein kinases (LRR-RLKs), including CLV1, BARELY ANY MERISTEMS and RECEPTOR-LIKE PROTEIN KINASE 2 (RPK2), a receptor-like protein CLV2 and a pseudokinase CORYNE (CRN) are involved in the perception of the CLV3 signal to repress WUS expression4-10. WUS, a homeodomain transcription factor, in turn directly activates CLV3 expression and promotes stem cell activity in the shoot apical meristem11,12. However, the signalling mechanism immediately following the perception of CLV3 by its receptors is poorly understood. Here, we show that a group of LRR-RLKs, designated as CLAVATA3 INSENSITIVE RECEPTOR KINASES (CIKs), have essential roles in regulating CLV3-mediated stem cell homeostasis. The cik1 2 3 4 quadruple mutant exhibits a significantly enlarged SAM, resembling clv mutants. Genetic analyses and biochemical assays demonstrated that CIKs function as co-receptors of CLV1, CLV2/CRN and RPK2 to mediate CLV3 signalling through phosphorylation. Our findings not only widen the understanding of the underlying mechanism of CLV3 signal transduction in regulating stem cell fate but also reveal a novel group of RLKs that function as co-receptors to possibly mediate multiple extrinsic and intrinsic signals during plant growth and development.

MLK1 and MLK2 Coordinate RGA and CCA1 Activity to Regulate Hypocotyl Elongation in Arabidopsis thaliana.

Gibberellins (GAs) modulate diverse developmental processes throughout the plant life cycle. However, the interaction between GAs and the circadian rhythm remains unclear. Here, we report that MUT9p-LIKE KINASE1 (MLK1) and MLK2 mediate the interaction between GAs and the circadian clock to regulate hypocotyl elongation in Arabidopsis thaliana DELLA proteins function as master growth repressors that integrate phytohormone signaling and environmental pathways in plant development. MLK1 and MLK2 interact with the DELLA protein REPRESSOR OF ga1-3 (RGA). Loss of MLK1 and MLK2 function results in plants with short hypocotyls and hyposensitivity to GAs. MLK1/2 and RGA directly interact with CIRCADIAN CLOCK ASSOCIATED1 (CCA1), which targets the promoter of DWARF4 (DWF4) to regulate its roles in cell expansion. MLK1/2 antagonize the ability of RGA to bind CCA1, and these factors coordinately regulate the expression of DWF4 RGA suppressed the ability of CCA1 to activate expression from the DWF4 promoter, but MLK1/2 reversed this suppression. Genetically, MLK1/2 act in the same pathway as RGA and CCA1 in hypocotyl elongation. Together, our results provide insight into the mechanism by which MLK1 and MLK2 antagonize the function of RGA in hypocotyl elongation and suggest that MLK1/2 coordinately mediate the regulation of plant development by GAs and the circadian rhythm in Arabidopsis.

Fackel interacts with gibberellic acid signaling and vernalization to mediate flowering in Arabidopsis.

MAIN CONCLUSION: Fackel (FK) is involved in the flowering of Arabidopsis mainly via the gibberellin pathway and vernalization pathway. This new function of FK is partially dependent on the FLOWERING LOCUS C ( FLC ). A common transitional process from vegetative stage to reproductive stage exists in higher plants during their life cycle. The initiation of flower bud differentiation, which plays a key role in the reproductive phase, is affected by both external environmental and internal regulatory factors. In this study, we showed that the Arabidopsis weak mutant allele fk-J3158, impaired in the FACKEL (FK) gene, which encodes a C-14 reductase involved in sterol biosynthesis, had a long life cycle and delayed flowering time in different photoperiods. In addition, FK overexpression lines displayed an earlier flowering phenotype than that of the wild type. These processes might be independent of the downstream brassinosteroid (BR) pathway and the autonomous pathway. However, the fk-J3158 plants were more sensitive than wild type in reducing the bolting days and total leaf number under gibberellic acid (GA) treatment. Further studies suggested that FK mutation led to an absence of endogenous GAs in fk-J3158 and FK gene expression was also affected under GA and paclobutrazol (PAC) treatment. Moreover, the delayed flowering time of fk-J3158 could be rescued by a 3-week vernalization treatment, and the expression of FLOWERING LOCUS C (FLC) was accordingly down-regulated in fk-J3158. We also demonstrated that flowering time of fk-J3158 flc double mutant was significantly earlier than that of fk-J3158 under the long-day (LD) conditions. All these results indicated that FK may affect the flowering in Arabidopsis mainly via GA pathway and vernalization pathway. And these effects are partially dependent on the FLOWERING LOCUS C (FLC).

Homologs of SCAR/WAVE complex components are required for epidermal cell morphogenesis in rice.

Filamentous actins (F-actins) play a vital role in epidermal cell morphogenesis. However, a limited number of studies have examined actin-dependent leaf epidermal cell morphogenesis events in rice. In this study, two recessive mutants were isolated: less pronounced lobe epidermal cell2-1 (lpl2-1) and lpl3-1, whose leaf and stem epidermis developed a smooth surface, with fewer serrated pavement cell (PC) lobes, and decreased papillae. The lpl2-1 also exhibited irregular stomata patterns, reduced plant height, and short panicles and roots. Molecular genetic studies demonstrated that LPL2 and LPL3 encode the PIROGI/Specifically Rac1-associated protein 1 (PIR/SRA1)-like and NCK-associated protein 1 (NAP1)-like proteins, respectively, two components of the suppressor of cAMP receptor/Wiskott-Aldrich syndrome protein-family verprolin-homologous protein (SCAR/WAVE) regulatory complex involved in actin nucleation and function. Epidermal cells exhibited abnormal arrangement of F-actins in both lpl2 and lpl3 expanding leaves. Moreover, the distorted trichomes of Arabidopsis pir could be partially restored by an overexpression of LPL2 A yeast two-hybrid assay revealed that LPL2 can directly interact with LPL3 in vitro Collectively, the results indicate that LPL2 and LPL3 are two functionally conserved homologs of the SCAR/WAVE complex components, and that they play an important role in controlling epidermal cell morphogenesis in rice by organising F-actin.