Biology subjects

Breakspear, A.

Publications and source records attributed to Breakspear, A..

7 recordsLinked to original sources

bioRxiv2026

Colletotrichum higginsianum effector ChEC108 binds a plasmodesmal HMA protein and elicits plant defence

To establish infection, phytopathogens deploy effectors to compromise host defences and facilitate invasive growth. As part of this, the battle for control of symplastic connectivity via plasmodesmata is a key determinant of infection outcomes, yet little is known about how fungal effectors directly exploit these channels, and in turn, how hosts defend them. Here, we have identified ChEC108 as a plasmodesmal-targeting, cell-to-cell mobile effector from the anthracnose fungus, Colletotrichum higginsianum. ChEC108 binds the plasmodesmal protein HEAVY METAL-ASSOCIATED (HMA) ISOPRENYLATED PLANT PROTEIN 6 (HIPP6) from Arabidopsis via a tetrahedral metal ion coordination site with either of its HMA domains. Constitutive in planta expression of ChEC108 induces plasmodesmal closure and the upregulation of defence-associated genes in a manner dependent on its capacity to bind HIPP6. Further, HIPP6 binding impairs cell-to-cell mobility of ChEC108. Alongside the finding that loss of ChEC108 favoured C. higginsianum infection, this suggests ChEC108-HIPP6 interaction at plasmodesmata positively regulates defence.

plant biology↗

bioRxiv2024

Plasmodesmal closure elicits stress responses

Plant cells are connected to their neighbors via plasmodesmata facilitating the exchange of nutrients and signaling molecules. During immune responses, plasmodesmata close, but how this contributes towards a full immune response is unknown. To investigate this, we developed two transgenic lines with which we could induce plasmodesmal closure independently of immune elicitors, using the over-active CALLOSE SYNTHASE3 allele icals3m and the C-terminus of PDLP1 to drive callose deposition at plasmodesmata. Induction of plasmodesmal closure increased the expression of stress responsive genes, salicylic acid accumulation and resistance to Pseudomonas syringae DC3000. More homogeneous plasmodesmal closure using icals3m also led to the accumulation of starch and sugars, decreased leaf growth, as well as hypersusceptibility to Botrytis cinerea. Based on the profile of responses, we conclude that plasmodesmal closure itself activates stress signaling, raising questions of what signals mediate this response and whether these responses occur in all circumstances when plasmodesmata close.

plant biology↗

bioRxiv2023

Cell-specialized chloroplast signaling orchestrates photosynthetic and extracellular reactive oxygen species for stress responses

Cellular responses to abiotic stress involve multiple signals including secondary messengers such as reactive oxygen species (ROS) and Ca2+, phytohormones such as abscisic acid (ABA) and chloroplast-to-nucleus retrograde signals such as 3-phosphoadenosine 5-phosphate (PAP). Mechanism(s) by which these messengers, produced in different subcellular compartments, intersect for cell regulation remain enigmatic. Previously we showed that the chloroplast retrograde signal PAP, similar to ABA, induces an increase in ROS levels in guard cells (Pornsiriwong et al, 2017). Here we demonstrate a mechanistic link enabling ABA and PAP to coordinate both chloroplast and plasma membrane ROS production. In whole leaves, PAP alters various ROS-related processes including plasmodesmal permeability as well as responses to ozone and the bacterial elicitor flg22, but mainly initiates processes that quench ROS during oxidative stress. Conversely, we show in guard cells, both PAP and ABA induce an increase in ROS levels in both chloroplasts via photosynthetic electron transport, and the apoplast via the RESPIRATORY BURST OXIDASE HOMOLOG (RBOH). Both subcellular ROS sources were necessary for ABA- and PAP-mediated stomatal closure. However, PAP signaling diverges from ABA by activating RBOHD, instead of RBOHF, for apoplastic ROS mediated stomatal closure. We identified three calcium-dependent protein kinases (CPKs) as the post-translational activators of RBOHD-mediated ROS production. CPK13, CPK32, and CPK34 were transcriptionally induced by PAP and concurrently activate RBOHD and the slow anion channel SLAC1 by phosphorylating two Serine (S) residues, including S120 which is also targeted by the core ABA signaling kinase OPEN STOMATA 1 (OST1). Consequently, overexpression of the PAP-induced CPKs rescues stomatal closure in ost1. Our data identify stomatal chloroplasts, to be nodes in the multifaceted cellular stress response networks as they are both sources and mediators of ROS and retrograde signals such PAP. Thus, chloroplasts are not just mediators of photosynthesis in response to, for example, excess light, but can serve as critical nodes in the multifaceted cellular stress response networks in specialized cells via retrograde signals, providing support to the concept of sensory plastids. Significance StatementThe chloroplast is an environmental sensor for stresses such as excess light and drought via the activation of photosynthetic-mediated retrograde signals. However, how does it function in specialized cells for which carbon fixation is secondary? Here we show the chloroplast is an important node to coordinate multiple plant signaling pathways in response to stresses such as drought. The chloroplast retrograde signal 3-phosphoadenosine 5-phosphate (PAP) plays multiple roles in reactive oxygen species (ROS) signaling and homeostasis. While PAP suppresses ROS in photosynthetic tissue, PAP instead induces guard cell ROS in chloroplasts and extracellular space to induce stomatal closure. We decipher how PAP-induced proteins activate both extracellular ROS production and anion channels for stomatal closure, thus providing a mechanism by which chloroplasts provide a strategic complement to canonical hormonal pathways in regulating plant physiological responses in specialized cells.

plant biology↗

bioRxiv2022

Comparative phyloproteomics identifies conserved plasmodesmal proteins

Plasmodesmata connect neighbouring plant cells across the cell wall. They are cytosolic bridges, lined by the plasma membrane and traversed by endoplasmic reticulum to connect these cell components between cells and tissues. While plasmodesmata are notoriously difficult to extract, tissue fractionation and proteomic analyses have yielded valuable knowledge of their composition. Most proteomic profiles originate from cell suspension cultures in which simple plasmodesmata dominate and have been exclusively generated from dicotyledonous plant species. Here we have generated two novel proteomes to expand tissue and taxonomic representation of plasmodesmata: one from mature Arabidopsis leaves and one from the moss Physcomitrium patens. We have leveraged these and existing data to perform a comparative analysis that, owing to comparing proteomes from an expanded taxonomic tree, allowed us to identify conserved protein families that are associated with plasmodesmata that likely serve as core structural or functional components. Thus, we identified {beta}-1,3-glucanases, C2 lipid-binding proteins and tetraspanins as core plasmodesmal components, with proteins from P. patens and Arabidopsis maintaining plasmodesmal association across diverse species. Our approach has not only identified elements of a conserved, core plasmodesmal proteome, but also demonstrated the added power offered by comparative analysis. Conserved plasmodesmal proteins establish a basis upon which ancient plasmodesmal function can be further investigated to determine the essential roles these structures play in multicellular organism physiology in the green lineages.

plant biology↗

bioRxiv2021

Effectors from a Bacterial Vector-Borne Pathogen Exhibit Diverse Subcellular Localization, Expression Profiles and Manipulation of Plant Defense

Climate change is predicted to increase the prevalence of vector borne disease due to expansion of insect populations. Candidatus Liberibacter solanacearum (CLso) is a phloem-limited pathogen associated with multiple economically important diseases in Solanaceous crops. Little is known about the strategies and pathogenicity factors CLso uses to colonize vector and host. We determined the CLso effector repertoire by predicting SEC secreted proteins across four different CLso haplotypes, investigated effector localization in planta, and profiled effector expression in vector and host. The localization of CLso effectors in Nicotiana revealed diverse eukaryotic subcellular targets. The majority of tested effectors were unable to suppress plant immune responses, indicating they possess unique activities. Expression profiling in tomato and the psyllid Bactericera cockerelli indicated CLso differentially interacts with its host and vector and can switch effector expression in response to the environment. This study reveals CLso effectors possess complex expression patterns, target diverse host organelles and the majority are unable to suppress host immune responses. A mechanistic understanding of Lso effector function will reveal novel targets and provide insight into phloem biology.

plant biology↗

bioRxiv2019

Chitin perception in plasmodesmata identifies subcellular, context-specific immune signalling in plants

The plasma membrane (PM) that lines plasmodesmata has a distinct protein and lipid composition, underpinning specific regulation of these connections between cells. The plasmodesmal PM can integrate extracellular signals differently from the cellular PM, but it is not known how this specificity is established or how a single stimulus can trigger independent signalling cascades in neighbouring membrane domains. Here we have used the fungal elicitor chitin to investigate signal integration and responses at the plasmodesmal PM. We found that the plasmodesmal PM employs a receptor complex composed of the LysM receptors LYM2 and LYK4 which respectively change their location and interactions in response to chitin. Downstream, signalling is transmitted via a specific phosphorylation signature of an NADPH oxidase and localised callose synthesis that causes plasmodesmata closure. This demonstrates the plasmodesmal PM deploys both plasmodesmata-specific components and differential activation of PM-common components to independently integrate an immune signal.

plant biology↗

bioRxiv2017

Speed breeding: a powerful tool to accelerate crop research and breeding

The growing human population and a changing environment have raised significant concern for global food security, with the current improvement rate of several important crops inadequate to meet future demand [1]. This slow improvement rate is attributed partly to the long generation times of crop plants. Here we present a method called speed breeding, which greatly shortens generation time and accelerates breeding and research programs. Speed breeding can be used to achieve up to 6 generations per year for spring wheat (Triticum aestivum), durum wheat (T. durum), barley (Hordeum vulgare), chickpea (Cicer arietinum), and pea (Pisum sativum) and 4 generations for canola (Brassica napus), instead of 2-3 under normal glasshouse conditions. We demonstrate that speed breeding in fully-enclosed controlled-environment growth chambers can accelerate plant development for research purposes, including phenotyping of adult plant traits, mutant studies, and transformation. The use of supplemental lighting in a glasshouse environment allows rapid generation cycling through single seed descent and potential for adaptation to larger-scale crop improvement programs. Cost-saving through LED supplemental lighting is also outlined. We envisage great potential for integrating speed breeding with other modern crop breeding technologies, including high-throughput genotyping, genome editing, and genomic selection, accelerating the rate of crop improvement.

plant biology↗