Endoplasmic Reticulum Bodies in the Lateral Root Cap Are Involved in the Direct Transport of Beta-Glucosidase to Vacuoles

MID1-COMPLEMENTING ACTIVITY regulates cell proliferation and development via Ca2+ signaling in Marchantia polymorpha

MID1-COMPLEMENTING ACTIVITY (MCA) is a land plant-specific, plasma membrane protein, and Ca2+ signaling component that responds to exogenous mechanical stimuli, such as touch, gravity, and hypotonic-osmotic stress, in various plant species. MCA is essential for cell proliferation and differentiation during growth and development in rice (Oryza sativa) and maize (Zea mays). However, the mechanism by which MCA mediates cell proliferation and differentiation via Ca2+ signaling remains unknown. Here, we address this question using the liverwort Marchantia polymorpha. We show that the M. polymorpha MCA ortholog, MpMCA, is highly expressed in actively dividing regions, such as apical notches in the thalli and developing gametangiophores, and that MpMCA is a plasma membrane protein. In vivo, Ca2+ imaging using a Ca2+ sensor (yellow cameleon) revealed that MpMCA is required for maintaining proper [Ca2+]cyt levels in the apical notch region, egg cells, and antheridium cells. Mpmca mutant plants showed severe cell proliferation and differentiation defects in the thalli, gametangiophores, and gametangia, resulting in abnormal development and unsuccessful fertilization. Furthermore, expression of the Arabidopsis MCA1 gene complemented most of the defects in the growth and development of the Mpmca mutant plants. Our findings indicate that MpMCA is an evolutionarily conserved Ca2+-signaling component that regulates cell proliferation and development across the life cycle of land plants.

Effective alignment method using a diamond notch knife for correlative array tomography

Correlative array tomography, combining light and electron microscopy via serial sections, plays a crucial role in the three-dimensional ultrastructural visualization and molecular distribution analysis in biological structures. To address the challenges of aligning fluorescence and electron microscopy images and aligning serial sections of irregularly shaped biological specimens, we developed a diamond notch knife, a new tool for puncturing holes using a diamond needle. The diamond needle featured a triangular and right-angled tip, enabling the drilling of deep holes upon insertion into the polished block face. This study describes the application of the diamond notch knife in correlative array tomography.

Quantitative proteomics analysis identified new interacting proteins of JAL30 in Arabidopsis

Jacalin-related lectins (JALs) are a unique group of plant lectins derived from the jacalin protein family, which play important roles in plant defense responses. JAL30/PBP1 (PYK10 binding protein 1) interacts with inactive PYK10, exerting negative regulatory control over the size of the PYK10 complex, which is formed and activated upon insect or pathogen invasion. However, the precise interplay between JAL30 and other components remains elusive. In this study, we found JAL30 as a nucleocytoplasmic protein, but no obvious phenotype was observed in jal30-1 single mutant. Through immunoprecipitation (IP) enrichment combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), dozens of new JAL30 interacting proteins were found in addition to several reported ones. Gene Ontology (GO) analysis revealed that these interacting proteins were highly related to the wounding and bacterial stimuli, suggesting their potential involvement in the jasmonate (JA) response. Importantly, the expression of JAL30 was induced by MeJA treatment, further highlighting its relevance in plant defense mechanisms. A novel JAL30 interacting protein, ESM1, was identified and its interaction with JAL30 was confirmed by Co-immunoprecipitation. Moreover, ESM1 was found as an O-GlcNAcylated protein, suggesting that JAL30 may possess glycosylated protein binding ability, particularly in O-GlcNAcylated protein and peptide recognition. Overall, our study provides valuable insights into the interacting protein network and biological function of JAL30, demonstrates the interaction between JAL30 and ESM1, and uncovers the potential significance of JAL30 in plant defense system, potentially through its association with PYK10 complex or JA response. SIGNIFICANCE: The biological functions of lectin proteins, including defense responses, immunity responses, signal transduction, have been well studied. Lectin proteins were also utilized to enrich glycosylated proteins for their specific carbohydrates binding capability. Jacalin-related lectins (JALs) were found to involve in plant defense mechanism. However, it is not yet clear whether JALs could use for enrichment of glycosylated proteins. In this study, we used label-free quantification method to identify interacting proteins of JAL30. A novel interacting protein, ESM1, as an O-GlcNAcylated protein was found. ESM1 has been reported to take part in defense against insect herbivory. Therefore, our findings provided experimental evidence to confirm that JALs have potential to be developed as the bio-tools to enrich glycosylated proteins. Finally, our data not only illustrated the vital biological role of JALs in plants, but also verified unique function of JAL30 in recognizing O-GlcNAcylated proteins.

A developmentally controlled cellular decompartmentalization process executes programmed cell death in the Arabidopsis root cap

Programmed cell death (PCD) is a fundamental cellular process crucial to development, homeostasis, and immunity in multicellular eukaryotes. In contrast to our knowledge on the regulation of diverse animal cell death subroutines, information on execution of PCD in plants remains fragmentary. Here, we make use of the accessibility of the Arabidopsis (Arabidopsis thaliana) root cap to visualize the execution process of developmentally controlled PCD. We identify a succession of selective decompartmentalization events and ion fluxes as part of the terminal differentiation program that is orchestrated by the NO APICAL MERISTEM, ARABIDOPSIS THALIANA ACTIVATING FACTOR, CUP-SHAPED COTYLEDON (NAC) transcription factor SOMBRERO. Surprisingly, the breakdown of the large central vacuole is a relatively late and variable event, preceded by an increase of intracellular calcium levels and acidification, release of mitochondrial matrix proteins, leakage of nuclear and endoplasmic reticulum lumina, and release of fluorescent membrane reporters into the cytosol. In analogy to animal apoptosis, the plasma membrane remains impermeable for proteins during and after PCD execution. Elevated intracellular calcium levels and acidification are sufficient to trigger cell death execution specifically in terminally differentiated root cap cells, suggesting that these ion fluxes act as PCD-triggering signals. This detailed information on the cellular processes occurring during developmental PCD in plants is a pivotal prerequisite for future research into the molecular mechanisms of cell death execution.

New insights into plant autophagy: molecular mechanisms and roles in development and stress responses

Autophagy is an evolutionarily conserved eukaryotic intracellular degradation process. Although the molecular mechanisms of plant autophagy share similarities with those in yeast and mammals, certain unique mechanisms have been identified. Recent studies have highlighted the importance of autophagy during vegetative growth stages as well as in plant-specific developmental processes, such as seed development, germination, flowering, and somatic reprogramming. Autophagy enables plants to adapt to and manage severe environmental conditions, such as nutrient starvation, high-intensity light stress, and heat stress, leading to intracellular remodeling and physiological changes in response to stress. In the past, plant autophagy research lagged behind similar studies in yeast and mammals; however, recent advances have greatly expanded our understanding of plant-specific autophagy mechanisms and functions. This review summarizes current knowledge and latest research findings on the mechanisms and roles of plant autophagy with the objective of improving our understanding of this vital process in plants.