The development of plant tissues requires cell–cell communication facilitated by chemical and peptide hormones, including small signaling peptides in the CLAVATA3/EMBRYO-SURROUNDING REGION (CLE) ...family. The paradigmatic CLE signaling peptide CLAVATA3 regulates the size of the shoot apical meristem and the expression of the stem cell–promoting WUSCHEL transcription factor through an unknown mechanism. This review discusses recent advances in CLE signaling, showing that CLE pathways are conserved in bryophytes, that CLE peptides in Arabidopsis thaliana regulate stem cell identity and cell division in root tissues, and connections to auxin biosynthesis in regulating flower and leaf development. These advances shed light on potential WUSCHEL family–independent aspects of CLE signaling and the overlap between CLE and auxin signaling
Physical exercise is generally beneficial to all aspects of human and animal health, slowing cognitive ageing and neurodegeneration
. The cognitive benefits of physical exercise are tied to an ...increased plasticity and reduced inflammation within the hippocampus
, yet little is known about the factors and mechanisms that mediate these effects. Here we show that 'runner plasma', collected from voluntarily running mice and infused into sedentary mice, reduces baseline neuroinflammatory gene expression and experimentally induced brain inflammation. Plasma proteomic analysis revealed a concerted increase in complement cascade inhibitors including clusterin (CLU). Intravenously injected CLU binds to brain endothelial cells and reduces neuroinflammatory gene expression in a mouse model of acute brain inflammation and a mouse model of Alzheimer's disease. Patients with cognitive impairment who participated in structured exercise for 6 months had higher plasma levels of CLU. These findings demonstrate the existence of anti-inflammatory exercise factors that are transferrable, target the cerebrovasculature and benefit the brain, and are present in humans who engage in exercise.
Sexual reproduction in flowering plants requires communication between synergid cells and a tip-elongating pollen tube (PT) for the successful delivery of sperm cells to the embryo sac. The reception ...of the PT relies on signaling within the synergid cell that ultimately leads to the degeneration of the receptive synergid and PT rupture, releasing the sperm cells for double fertilization. In Arabidopsis (Arabidopsis thaliana), NORTIA, a member of the MILDEW RESISTANCE LOCUS O (MLO) family of proteins, plays a critical role in the communication processes regulating PT reception. In this study, we determined that MLO function in PT reception is dependent on MLO protein localization into a Golgi-associated compartment before PT arrival, indicating that PT-triggered regulation of the synergid secretory system is important for synergid function during pollination. Additionally, a structure-function analysis revealed that MLO homooligomerization, mediated by the amino-terminal region of the protein, and carboxyl-terminal tail identity both contribute to MLO activity during PT reception.
Cell division is often regulated by extracellular signaling networks to ensure correct patterning during development. In Arabidopsis, the SHORT-ROOT (SHR)/SCARECROW (SCR) transcription factor dimer ...activates CYCLIND6;1 (CYCD6;1) to drive formative divisions during root ground tissue development. Here, we show plasma-membrane-localized BARELY ANY MERISTEM1/2 (BAM1/2) family receptor kinases are required for SHR-dependent formative divisions and CYCD6;1 expression, but not SHR-dependent ground tissue specification. Root-enriched CLE ligands bind the BAM1 extracellular domain and are necessary and sufficient to activate SHR-mediated divisions and CYCD6;1 expression. Correspondingly, BAM-CLE signaling contributes to the restriction of formative divisions to the distal root region. Additionally, genetic analysis reveals that BAM-CLE and SHR converge to regulate additional cell divisions outside of the ground tissues. Our work identifies an extracellular signaling pathway regulating formative root divisions and provides a framework to explore this pathway in patterning and evolution.
Ligand recognition by cell-surface receptors underlies development and immunity in both animals and plants. Modulating receptor signalling is critical for appropriate cellular responses but the ...mechanisms ensuring this are poorly understood. Here, we show that signalling by plant receptors for pathogen-associated molecular patterns (PAMPs) in immunity and CLAVATA3/EMBRYO SURROUNDING REGION-RELATED peptides (CLEp) in development uses a similar regulatory module. In the absence of ligand, signalling is dampened through association with specific type-2C protein phosphatases. Upon activation, PAMP and CLEp receptors phosphorylate divergent cytosolic kinases, which, in turn, phosphorylate the phosphatases, thereby promoting receptor signalling. Our work reveals a regulatory circuit shared between immune and developmental receptor signalling, which may have broader important implications for plant receptor kinase-mediated signalling in general.
Summary
In flowering plants, cell–cell communication plays a key role in reproductive success, as both pollination and fertilization require pathways that regulate interactions between many different ...cell types. Some of the most critical of these interactions are those between the pollen tube (PT) and the embryo sac, which ensure the delivery of sperm cells required for double fertilization. Synergid cells function to attract the PT through secretion of small peptides and in PT reception via membrane‐bound proteins associated with the endomembrane system and the cell surface. While many synergid‐expressed components regulating PT attraction and reception have been identified, few tools exist to study the localization of membrane‐bound proteins and the components of the endomembrane system in this cell type. In this study, we describe the localization and distribution of seven fluorescent markers that labelled components of the secretory pathway in synergid cells of Arabidopsis thaliana. These markers were used in co‐localization experiments to investigate the subcellular distribution of the two PT reception components LORELEI, a GPI‐anchored surface protein, and NORTIA, a MILDEW RESISTANCE LOCUS O protein, both found within the endomembrane system of the synergid cell. These secretory markers are useful tools for both reproductive and cell biologists, enabling the analysis of membrane‐associated trafficking within a haploid cell actively involved in polar transport.
Significance Statement
Flowering plant reproduction requires the coordination of intercellular communication pathways between specialized cells regulating pollen tube attraction and reception. In this study, we generated a suite of fluorescent markers labeling key components of the secretory pathway and stably expressed them in the synergid cells of Arabidopsis thaliana, enabling the detailed analysis of the regulation of cellular trafficking in a haploid cell.
Key message
MLOs in Plant Reproduction.
The MILDEW RESISTANCE LOCUS-O (MLO) protein family, comprised of 15 members, plays roles in diverse cell–cell communication processes such as powdery mildew ...susceptibility, root thigmomorphogenesis, and pollen tube reception. The
NORTIA
(
NTA
,
AtMLO7
) gene is expressed in the synergid cells of the female gametophyte where it functions in intercellular communication with the pollen tube. Discrepancies between previously published promoter::GUS and promoter::gene-GUS constructs expression patterns led us to explore the regulation of
NTA
expression. Here we found via NTA
pro
::gNTA-GUS truncations that sequences within the
NTA
gene negatively regulate its expression in the stomata and carpel walls. This led to the hypothesis that other
MLO
family members may also have additional regulatory sequences within the gene. MLO
pro
::gMLO-GUS constructs were examined for each family member focusing specifically on flowers in order to determine whether other MLOs could play a role in reproductive cell–cell communication. Notably, several
MLO
s were expressed in the pollen, in the stigma, in the pollinated style, and in the synergids and central cell. These findings indicate that other MLOs in addition to NTA could play a role in reproduction. Previous studies on the MLO family showed that phylogenetically related MLOs had redundant functions in powdery mildew infection and root thigmomorphogenesis; however,
MLO
expression in reproductive tissues did not strictly follow phylogenetic relationships, indicating that MLOs from different evolutionary origins may have been recruited for function in sexual reproduction.
Plants use cell to cell signaling to coordinate their development with their environment, and the activities of plant meristems that iteratively produce new organs must be tightly controlled to ...ensure fitness and reproductive success. Initial cells (or stem cells) coordinate with surrounding cells in meristems to make cell fate and cell division decisions that pattern plant tissues. Small peptides in the CLAVATA3 ENDOSPERM SURROUNDING REGION (CLE) family initiate cell-cell communication pathways that control meristem activity and therefore plant development in all plant species studied to date, and in both root and shoot apical meristems. However, until recently there was little mechanistic understanding of the events that take place after a CLEp ligand binds its receptor. Here we demonstrate a novel role for CLEp signaling in promoting cell division in root ground tissue; the control of cell division by CLEps appears to be a conserved feature of CLEp signaling in multiple tissues. Additionally, we describe novel signal transduction components of CLEp signaling and connect them to other components of CLEp signaling, providing mechanisms for CLEp signaling processes. The PBS1-LIKE34/35/36 (PBL34/35/36) receptor-like cytoplasmic kinases operate downstream of the CLEp receptors to promote signaling by inhibiting the POLTERGEIST phosphatase that negatively regulates CLEp receptors. We also show that PBLs likely phosphorylate PLANT U-BOX4 (PUB4) to promote CLEp signaling, which may require EXTRA LARGE G1/2/3 (XLG1/2/3) proteins to scaffold this interaction. XLG1/2/3 and ARABIDOPSIS G PROTEIN BETA1 (AGB1) are both required for CLEp perception, therefore heterotrimeric g proteins may operate in CLEp signaling with PBL34/35/36 and PUB4. The cytoplasmic requirements for CLEp signaling remain a long outstanding question and these findings make important steps in the understanding of aspects of plant development crucial to crop improvement.
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