Stomata, specialized structures of plant epidermis, are crucial for gas (e.g., CO 2 , O 2 , and H 2 O) exchange between plants and the environment. Stomatal density and pattern are governed by ERECTA family (ERf) receptor-like kinases-controlled signaling. Clathrin-mediated endocytosis (CME) is a new mechanism for the internalization of receptors to activate the downstream signaling in animals. Here, we found that mutation of CME components resulted in formation of stomatal clusters and thus increased stomatal index. The adaptor protein 2σ (AP2σ) subunit of CME interacted with ERf. ERf receptor internalization required CME. Furthermore, the ERf receptor motifs were identified to be recognized by AP2σ. Genetic analysis showed that CME components CHC2, CLC2, and CLC3 acted downstream of EPIDERMAL PATTERNING FACTOR 1/2 while upstream of YODA and worked together with ERf to regulate stomatal development. Consistently, EPF2-induced MAPK activation was significantly reduced in chc2-2 clc2 clc3 and ap2μ clc2 clc3 mutants or when the ERf endocytic motifs were mutated, leading to stabilized SPEECHLESS protein and misregulated stomatal lineage progression. Overall, our findings demonstrate that activation of the ERf receptors via internalization is essential for stomatal development, establishing a mechanism of CME-mediated receptor internalization activation in plants.

Autophagy must be dynamically tuned to nutrient availability, yet how plants prevent excessive autophagy during nutrient starvation while preserving basal flux under replete conditions remains elusive. Here, we identify the redundant U-box E3 ligases PUB25 and PUB26 as critical negative regulators of nitrogen starvation-induced autophagy in Arabidopsis. Loss of PUB25/PUB26 enhances autophagy and improves plant growth under nitrogen deprivation, whereas their overexpression suppresses autophagy. Mechanistically, PUB25/PUB26 directly interacts with the autophagy-initiating kinase ATG1 and target it for proteasomal degradation. During nitrogen starvation, the receptor kinase FERONIA (FER) is transcriptionally upregulated and enhances PUB25/PUB26 activity by phosphorylating it at Thr95/Thr94, acting as a molecular brake on ATG1 to fine-tune autophagy to proper cellular levels during prolonged deprivation. Additionally, under nitrogen-rich conditions, FER directly phosphorylates ATG13 to repress ATG1-ATG13 complex assembly, thereby sustaining low basal autophagy. Together, our findings reveal a nutrient-responsive FER-PUB25/PUB26 regulatory module that integrates constitutive and inducible regulatory checkpoints to dynamically modulate autophagy activity across variable nitrogen status, optimizing plant fitness.

Cereal crops, predominantly belonging to the grass family (Poaceae), are the cornerstone of global agriculture; thus, improving their environmental adaptability has emerged as a pivotal research focus. Stomata, which act as essential conduits mediating gas exchange and water loss in plants, are key targets for genetic modification to enhance crop drought tolerance and water use efficiency (WUE). Unlike the two-celled stomatal complexes of Arabidopsis thaliana, grasses possess four-celled stomata (two dumbbell-shaped guard cells flanked by two subsidiary cells, SCs) with distinct developmental mechanisms, which makes them critical for grasses to adapt to adverse environments. This review summarizes recent advances in understanding such species-specific developmental mechanisms in grasses, with three core emphases: Firstly, grasses possess four-celled stomatal complexes with distinct vein-proximal patterning, and plasticity of stomatal density in response to environmental stimuli (e.g., CO2, drought stress, temperature, and light) among species; Secondly, functional characterization of key regulators (e.g., BASIC HELIX-LOOP-HELIX (bHLH) transcription factors) governing distinct stomatal developmental stages (e.g., initiation, division, differentiation), and their potential for genetic manipulation to optimize stomatal traits for improved WUE and drought resistance; Lastly, the integration of multi-omics approaches, including single-cell RNA-seq (scRNA-seq), spatial transcriptomics (ST), pan-genomics, genome-wide association studies (GWAS), and artificial intelligence (AI)-driven data mining for accelerating the identification of novel regulators and genotype-phenotype associations in more grass crops. This review provides a comprehensive framework for understanding grass-specific stomatal development and offers actionable targets for precision breeding of drought-resilient cereal crops.

Functional stomata depend on paired guard cells that arise from a single symmetric division of the guard mother cell (GMC). However, the mechanism governing this division in grasses with unique dumbbell-shaped guard cells remains poorly understood. Here, we identify OsCYCD7;1 as an essential component for GMC division in rice. OsCYCD7;1 was strictly confined to pre-divisional GMCs, and its knockout prevented GMC division. OsSMR9, a plant CDK (cyclin-dependent kinase) inhibitor, physically interacted with OsCYCD7;1 and suppressed GMC division. Yeast one-hybrid (Y1H) and EMSA assays revealed OsMUTE directly bound to OsCYCD7;1 promoter. Consistently, OsCYCD7;1 expression was repeatedly detected in ectopically dividing GMCs of osmute mutant. This ectopic division was markedly suppressed in oscycd7;1 osmute but enhanced by OsCYCD7;1 overexpression in osmute. Moreover, a similar enhancement was observed in osflp osmute. Furthermore, Y1H and dual-luciferase assays indicated OsMUTE also bound to and activated OsSMR9. We demonstrate that OsCYCD7;1 is essential for GMC division. Specifically, its activity is inhibited through OsMUTE-activated OsSMR9, and its expression is negatively influenced by OsMUTE and OsFLP, which likely function together to ensure a single symmetric GMC division in rice. Our data expand grass-specific GMC division of stomatal development, fundamentally diverging from Arabidopsis.

The plant hormone abscisic acid (ABA) plays an important role in plant growth, development and abiotic stresses. ABA perception is mediated by its receptors, PYRABACTIN RESISTANCE 1 (PYR1)/PYR1-like (PYL) proteins (collectively referred to as PYLs), which initiate downstream ABA signaling. The functional regulation of PYLs, particularly through post-translational modifications (PTMs) is gradually attracting extensive attention. Here, we have summarized recent advances in research on PTMs of PYL family, highlighting how mechanisms such as phosphorylation, ubiquitination and nitration fine-tune their activity, stability and subcellular localization. We also briefly review the biological function and genetic phenotypes of PYL family, underscoring their central role in ABA signaling and stress adaptive responses in plants. Future studies should address key questions regarding the additional PTMs, specific sites and crosstalk of these PTMs.

In eukaryotes, XERODERMA PIGMENTOSUM GROUP D (XPD) is an integral subunit of the DNA repair/transcription complex TFIIH. In animals, XPD has been implicated in TFIIH-independent complexes regulating cell division, which, however, remains poorly understood in plants. Here, we identified XPD as a novel regulator of stomatal development in Arabidopsis. Its loss-of-function mutants exhibited increased stomatal precursor cells and formed stomatal clusters. Genetic analysis showed that XPD functions upstream of SPEECHLESS (SPCH) to control stomatal lineage entry, coordinates with MUTE to regulate meristemoid division and works together with FLP and FAMA to restrict GMC division. In a search of XPD interactors, we identified CDKA;1, which serves as both an essential cyclin-dependent kinase and a key SPCH activator. Consistently, xpd mutants exhibited enhanced stomatal lineage cell divisions and elevated SPCH protein levels. Furthermore, XPD acts upstream of CDKA;1, as expression of the dominant-negative CDKA;1.N146 allele significantly suppressed the excessive cell division and stomatal development defects in xpd plants. Our data highlight the precise regulation of stomatal development by XPD, expanding its critical TFIIH-independent roles in plant cell division and fate specification.

As sessile organisms, plants have evolved diverse and sophisticated mechanisms to rapidly sense and adapt to environmental stresses. The initial stress perception involves the activation of membrane-localized receptor kinases and the rapid opening of calcium channels, which constitutes the earliest response phase of stress signaling. Subsequently, mitogen-activated protein kinase (MAPK) cascades act as central signaling modules that transduce stress signals, decoding the initial perception into specific cellular responses (e.g., transcriptional activation). Specifically, under salt stress, MAPK activities are precisely regulated by upstream kinases (e.g., MAPKKs) and phosphatases (e.g., PP2C family proteins). Accordingly, these cascades orchestrate critical downstream processes, including hormone signaling crosstalk, ion, and redox homeostasis maintenance, thereby fine-tuning the trade-off between plant growth and stress resistance. In this review, we summarized the functions and molecular mechanisms of MAPKs in coordinating plant growth with stress adaptation capacity. Furthermore, we discussed their potential applications in molecular breeding for improving crop salt tolerance.

The shoot apical meristem (SAM) serves as the cellular source of aboveground plant development and is precisely regulated by a complex interplay of genetic, hormonal, and environmental factors. Central to this regulation is the CLAVATA3 (CLV3)–WUSCHEL (WUS) negative feedback loop, which maintains SAM homeostasis by balancing stem cell proliferation and differentiation. Among the diverse regulatory mechanisms, reversible protein phosphorylation, which is mediated by protein kinases and phosphatases, has emerged as a key posttranslational modification that integrates internal and external signals to modulate SAM activity. This review summarizes recent advances in understanding the roles of kinases and phosphatases in SAM maintenance, with a particular focus on phosphorylation-mediated control of the CLV3–WUS pathway and associated signaling networks. By synthesizing these molecular insights, we aim to provide a comprehensive reference for deciphering the regulatory mechanisms underlying SAM homeostasis. A deeper understanding of SAM regulation not only advances fundamental knowledge of plant developmental biology but also holds significant potential for improving crop architecture and agricultural productivity.

Cold environments significantly influence plant growth, development, geographical distribution, and yield. A growing body of research has focused on elucidating the molecular mechanisms underlying plant responses to cold stress, among which post-translational modifications (PTMs) of proteins play a pivotal role by regulating protein stability, activity, and protein-protein interactions. In this review, we summarize regulatory mechanisms of several types of PTMs, including phosphorylation, ubiquitination, SUMOylation, acetylation, crotonylation, and S-acylation, in the cold stress signaling pathway. These dynamic modifications allow plants to mount precise and adaptive responses, effectively balance defense with developmental processes, and establish a molecular foundation for adaptation to cold environments. A comprehensive understanding of the cascading relationships and collaborative regulatory networks among PTMs is indispensable for deciphering the molecular logic of plant cold adaptation. Moreover, further exploration of the temporal and spatial dynamics of these modifications and their functional associations will continue to refine our mechanistic understanding of the regulatory networks governing plant cold tolerance.

Type one protein phosphatases (TOPPs) widely modulate phytohormone signaling and stress responses, but their roles in ethylene signaling remain unknown. This study reveals a reciprocal regulatory relationship between TOPPs and ethylene insensitive 2 (EIN2)-mediated ethylene signaling. We identified that ethylene can induce TOPPs' expression, and topp1/4/5 mutants exhibited partial ethylene insensitivity with reduced EIN3 protein. Mechanistically, TOPPs function upstream of EIN2 and interact with its carboxyl-terminal domain (CEND) to dephosphorylate the S655 residue. This site-specific dephosphorylation promotes EIN2 stability and EIN2 CEND nuclear accumulation, thereby activating ethylene responses. Notably, EIN2S655A-YFP/ein2-5 plants displayed constitutive ethylene responses and improved salt tolerance. Further investigation showed that EIN3/EIN3 like 1 (EIL1) activates TOPPs' expression by binding to their promoters, amplifying ethylene signaling accordingly. Together, our finding establishes TOPPs as key regulators in ethylene signaling and reveal a dephosphorylation switch mechanism governing EIN2 function, providing critical insight into how EIN2 posttranslational modifications mediate plant stress adaptation.

Stomata, composed of paired guard cells, serve as essential pores for plant-atmosphere gas exchange and undergo tightly regulated development. FOUR LIPS (FLP), the first characterized regulator of stomatal development, has been studied for three decades. It encodes an atypical R2R3-MYB transcription factor that restricts guard mother cell division by repressing several core cell cycle genes. This factor exhibits partial functional redundancy with bHLH proteins FAMA and MUTE during stomatal fate commitment and differentiation. Its stomatal regulatory function is conserved across plant species. Notably, broad FLP expression across tissues enables functions beyond stomata, including roles in root gravitropism, lateral root initiation, female gametophyte development, and leaf angle determination. Furthermore, FLP is induced by environmental cues such as drought, salt, and cold stress to mediate adaptive responses. Here, we summarize the current understanding of FLP, focusing on conserved stomatal mechanisms and highlighting its functional versatility across plant systems.

Epidermal hairs are specialized structures on the epidermis of plants that function in crop defense against biotic and abiotic stresses, particularly in warding off herbivores and pests. However, the regulatory mechanism governing epidermal hair formation in rice remains unclear. Here, we report that OsSCR1 (SCARECROW1) and OsSCR2 redundantly promote development of three types of rice trichomes (macro hairs, micro hairs, and glandular hairs), as shown through the reduced and increased trichomes in their knockout and overexpression lines. We demonstrate that OsSCR1 acts upstream of OsWOX3B (WUSCHEL-RELATED HOMEOBOX 3B) in that overexpression of OsWOX3B could rescue the macro hair development defects in osscr1 osscr2 double mutants, and that OsSCR1 protein activates OsWOX3B expression using luciferase activity and chromatin immunoprecipitation quantitative PCR (ChIP-qPCR) assays. In addition, OsSPL10 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE10) acts upstream of OsSCR1 and enhances its expression to promote the development of macro and micro hairs. Additionally, increasing leaf trichome density through overexpressing OsSCR2 could enhance seedling resistance to locust feeding. Collectively, our findings indicate that OsSPL10 facilitates the process of OsSCR1 inducing OsWOX3B activity to promote the formation of macro and micro hairs in rice.

COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) is a highly conserved eukaryotic protein that functions as a central repressor in plant photomorphogenesis. As an E3 ubiquitin ligase, COP1 regulates various physiological processes by ubiquitinating and degrading specific substrates. In recent years, the multifunctionality of COP1 has garnered increasing attention, as it not only is involved in light signal transduction but also plays a critical regulatory role in plant growth and development, stress response pathways, and hormone signaling networks. Moreover, COP1 also participates in the cross-regulation of multiple signaling pathways, including light signaling, stress response, and hormone signaling, further highlighting its core position in plant environment adaptation and growth and development. This review systematically elaborates on the evolutionary conservation, structural features, and multifunctionality of COP1, with a focus on summarizing its molecular regulatory networks in growth, development, and stress responses, while exploring its potential applications in crop genetic improvement.

Maize (Zea mays L.) growth and yield are severely limited by drought stress worldwide. Stomata play crucial roles in transpiration and gas exchange and are thus essential for improving plant water-use efficiency (WUE) to help plants deal with the threat of drought. In this study, we characterized the maize dsd1 (decreased stomatal density 1) mutant, which showed defects in stomatal development, including guard mother cell differentiation, subsidiary cell formation and guard cell maturation. DSD1 encodes the basic helix-loop-helix transcription factor INDUCER OF CBF EXPRESSION b (ZmICEb) and is a homolog of ICE1 in Arabidopsis (Arabidopsis thaliana). DSD1/ZmICEb is expressed in stomatal file cells throughout stomatal development and plays a conserved role in stomatal development across maize and Arabidopsis. Mutations in DSD1/ZmICEb dramatically improved drought tolerance and WUE in maize and reduced yield losses under drought conditions. Therefore, DSD1/ZmICEb represents a promising candidate target gene for the genetic improvement of drought tolerance in maize by manipulating stomatal density.

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.

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.

Drought is one of the most severe environmental factors limiting plant growth and crop yield, necessitating the identification of genes that enhance drought resistance for crop improvement. Through screening an ethyl methyl sulfonate-mutagenized rice mutant library, we isolated the PEG tolerance mutant 97-1 (ptm97-1), which displays enhanced resistance to osmotic and drought stress, and increased yield under drought conditions. A point mutation in OsMATE6 was identified as being associated with the drought-resistant phenotype of ptm97-1. The role of OsMATE6 in conferring drought resistance was confirmed by additional OsMATE6 knockout mutants. OsMATE6 is expressed in guard cells, shoots and roots and the OsMATE6-GFP fusion protein predominantly localizes to the plasma membrane. Our ABA efflux assays suggest that OsMATE6 functions as an ABA efflux transporter; mutant protoplasts exhibited a slower ABA release rate compared to the wild type. We hypothesize that OsMATE6 regulates ABA levels in guard cells, influencing stomatal closure and enhancing drought resistance. Notably, OsMATE6 knockout mutants demonstrated greater yields under field drought conditions compared to wild-type plants, highlighting OsMATE6 as a promising candidate for improving crop drought resistance.

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.

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.

In plants, autophagy is a conserved process by which intracellular materials, including damaged proteins, aggregates, and entire organelles, are trafficked to the vacuole for degradation, thus maintaining cellular homeostasis. The past few decades have seen extensive research into the core components of the central autophagy machinery and their physiological roles in plant growth and development as well as responses to biotic and abiotic stresses. Moreover, several methods have been established for monitoring autophagic activities in plants, and these have greatly facilitated plant autophagy research. However, some of the methodologies are prone to misuse or misinterpretation, sometimes casting doubt on the reliability of the conclusions being drawn about plant autophagy. Here, we summarize the methods that are widely used for monitoring plant autophagy at the physiological, microscopic, and biochemical levels, including discussions of their advantages and limitations, to provide a guide for studying this important process.