Score: 30.7, Published: 2024-02-15
DOI: 10.1101/2024.02.14.580413
Secreted immune proteases Rcr3 and Pip1 of tomato are both inhibited by Avr2 from the fungal plant pathogen Cladosporium fulvum but only Rcr3 act as a decoy co-receptor that detects Avr2 in the presence of the Cf-2 immune receptor. Here, we identified crucial Rcr3 residues for Cf-2-mediated signalling and bioengineered various proteases to trigger Avr2/Cf-2 dependent immunity. Despite substantial divergences in Rcr3 orthologs from eggplant and tobacco, only minimal alterations were sufficient to trigger Avr2/Cf-2-triggered immune signalling. Tomato Pip1, by contrast, was bioengineered with 16 Rcr3-specific residues to initiate Avr2/Cf-2-triggered immune signalling. These residues cluster on one side next to the substrate binding groove, indicating a potential Cf-2 interaction site. Our findings also revealed that Rcr3 and Pip1 have distinct substrate preferences determined by two variant residues and that both proteases are suboptimal for binding Avr2. This study advances our understanding of the evolution of Avr2 perception and opens avenues to bioengineer proteases to broaden pathogen recognition in other crops.
Score: 12.9, Published: 2024-02-15
DOI: 10.1101/2024.02.15.580496
Epigenetic gene silencing by Polycomb Repressive Complex 2 (PRC2) is essential for development in eukaryotes, yet what initiates silencing is still unclear. Polycomb silencing at Arabidopsis FLOWERING LOCUS C (FLC) requires PRC2 and accessory proteins VIN3 and VRN5, both containing a structurally conserved polymerization module. Here, we show that polymerization of the VIN3 VEL domain increases the size of nuclear assemblies, with enhanced local concentration promoting chromatin association. This increased avidity enables effective H3K27me3 nucleation, underlying the digital switch to an epigenetically silenced state. However, VRN5 VEL is not essential for this PRC2 nucleation and VRN5 VEL is unable to replace VIN3 VEL function. This work thus defines a specific role for polymerization-mediated multivalency in initiating and maintaining PRC2 nucleation and extends our understanding of the principles that initiate epigenetic silencing.
Score: 12.0, Published: 2024-02-15
DOI: 10.1101/2024.02.13.579726
Eudicot plant species have bifacial leaves with each surface varying in a diversity of components, resulting in potentially different microhabitats for pathogens. We tested how Botrytis cinerea, a necrotroph fungal pathogen, interacts with the two different leaf surfaces across 16 crop species and 20 Arabidopsis genotypes. This showed that the abaxial surface is generally more susceptible to the pathogen than the adaxial surface. In Arabidopsis, the differential lesion area between leaf surfaces was associated to jasmonic acid (JA) and salicylic acid (SA) signaling and differential induction of defense chemistry. When infecting the adaxial surface, leaves mounted stronger defenses by producing more glucosinolates and camalexin defense compounds, partially explaining the differential susceptibility across surfaces. Testing a collection of 96 B. cinerea strains showed genetic heterogeneity of growth patterns, with a few strains preferring the adaxial surface while most are more virulent on the abaxial surface. Overall, we show that leaf-Botrytis interactions are complex with host-specific, surface-specific, and strain-specific behaviors. Within Arabidopsis, this mechanistically links to potential variation in JA/SA signaling across the two surfaces.
Score: 11.7, Published: 2024-02-12
DOI: 10.1101/2024.02.12.579879
In photosynthetic organisms light acts as an environmental signal to control their development and physiology, and as energy source to drive the conversion of CO2 into carbohydrates used for growth or storage. The main storage carbohydrate in green algae is starch, which accumulates during the day and is broken down at night to meet cellular energy demands. The signalling role of light quality in the regulation of starch accumulation remains unexplored. Here, we report that in the model green alga Chlamydomonas reinhardtii blue light perceived by the photoreceptor PHOTOTROPIN causes dephosphorylation of the PHOTOTROPIN-MEDIATED SIGNALLING KINASE 1 that then suppresses starch accumulation by inhibiting the expression of GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE. Our results provide an in-depth view of how photoreceptor-mediated signalling controls microalgal carbon metabolism. One-Sentence SummaryBlue light perception by PHOTOTROPIN triggers kinase-mediated signaling to inhibit starch accumulation in the green alga Chlamydomonas.
Score: 8.4, Published: 2024-02-17
DOI: 10.1101/2024.02.14.580295
The ATP-driven bicarbonate transporter BCT1, a four-component complex in the cyanobacteria CO2-concentrating mechanism (CCM), could enhance photosynthetic CO2 assimilation in plant chloroplasts. However, directing its subunits (CmpA, CmpB, CmpC and CmpD) to three chloroplast sub-compartments is highly complex. Investigating BCT1 integration into Nicotiana benthamiana chloroplasts revealed promising targeting strategies using transit peptides from the intermembrane space (IMS) protein Tic22 for correct CmpA targeting, while the transit peptide of the chloroplastic ABCD2 transporter effectively targeted CmpB to the inner envelope membrane (IEM). CmpC and CmpD were targeted to the stroma by RecA and recruited to the IEM by CmpB. Despite successful targeting, expression of this complex in CO2-dependent E. coli provided no bicarbonate uptake. We then used rational design and directed evolution to generate new BCT1 forms which were always active. Several mutants were recovered, including a CmpCD fusion. Selected mutants were further characterized and stably expressed in Arabidopsis but the transformed plants did not have higher carbon assimilation rates or decreased CO2 compensation points in mature leaves. While further analysis is required, this directed evolution and heterologous testing approach presents potential for iterative modification and assessment of CCM components to improve plant photosynthesis.
Score: 8.0, Published: 2024-02-15
DOI: 10.1101/2024.02.14.580303
Digitalis purpurea (foxglove) is a widely distributed ornamental plant and the producer of the biomedical compound digoxin. Here, we present a long read sequencing-based genome sequence of a red flowering D. purpurea plant and a corresponding prediction of gene models. The high assembly continuity is indicated by the N50 of 4.3 Mbp and the completeness is supported by discovery of about 96% complete BUSCO genes. This genomic resource paves the way for an in-depth investigation of the flower pigmentation of D. purpurea. Structural genes of the anthocyanin biosynthesis and the corresponding transcriptional regulators were identified. The comparison of red and white flowering plants revealed a large insertion in the anthocyanidin synthase gene in white flowering plants that most likely renders this gene non-functional and could explain the loss of anthocyanin pigmentation. In addition, the anthocyanin biosynthesis activator MYB5 shows a 18 bp deletion in white flowering plants that results in the loss of 6 amino acids in the protein.
Score: 7.1, Published: 2024-02-14
DOI: 10.1101/2024.02.12.579961
Reactive oxygen species (ROS) function as key signals in plants to enable adaptation to environmental stresses. Plant roots respond to transient water stress by temporarily ceasing branching using the acclimative response xerobranching1. In this study, we report that a rapid ROS burst regulates Xerobranching by inducing multimerization of auxin repressor protein IAA3/SHY2. Mutations in specific cysteine residues in IAA3/SHY2 disrupt redox-mediated multimerization and interaction with co-repressor TPL, but not with auxin response partner ARF7 and auxin receptor TIR1. ROS-mediated oligomerization of IAA3/SHY2 is required for efficient ARF mediated target gene repression during Xerobranching and lateral root emergence. We demonstrate that AUX/IAA proteins vary in their redox mediated multimerization, revealing a new auxin response regulatory mechanism that directly connects ROS sensing to auxin signalling. Our study reveals how ROS, auxin and water stress intersect to shape acclimative responses in plant roots and maintain their phenotypic plasticity.
Score: 5.8, Published: 2024-02-15
DOI: 10.1101/2024.02.13.580128
Plant cell walls contain a meshwork of cellulose fibers embedded into a matrix of other carbohydrate and non-carbohydrate-based biopolymers. This composite material exhibits extraordinary properties, from stretchable and pliable cell boundaries to solid protective shells. Cellulose, a linear glucose polymer, is synthesized and secreted across the plasma membrane by cellulose synthase (CesA). Plants express several CesA isoforms, with different subsets necessary for primary and secondary cell wall biogenesis. The produced cellulose chains can be organized into fibrillar structures and fibrillogenesis likely requires the supramolecular organization of CesAs into pseudo sixfold symmetric complexes (CSCs). Here, we structurally and functionally characterize a set of soybean (Gm) CesA isoforms implicated in primary cell wall biogenesis. Cryogenic electron microscopy analyses of catalytically active GmCesA1, GmCesA3, and GmCesA6 reveal their assembly into homotrimeric complexes, stabilized by a cytosolic plant conserved region. Contrasting secondary cell wall CesAs, a peripheral position of the C-terminal transmembrane helix creates a large, lipid-exposed lateral opening of the enzymes cellulose-conducting transmembrane channels. Co-purification experiments reveal that homotrimers of different CesA isoforms interact in vitro and that this interaction is independent of the enzymes N-terminal cytosolic domains. Our data suggest that cross-isoform interactions are mediated by the class-specific region, which forms a hook-shaped protrusion of the catalytic domain at the cytosolic water-lipid interface. Further, inter-isoform interactions lead to synergistic catalytic activity, suggesting increased cellulose biosynthesis upon homotrimer interaction. Combined, our structural and biochemical data favor a model by which homotrimers of different CesA isoforms assemble into a microfibril-producing CSC.
Score: 5.8, Published: 2024-02-15
DOI: 10.1101/2024.02.14.580362
Temperature serves as a crucial environmental cue governing the growth and adaptation of plants in their natural habitat. The B-BOX proteins play a vital role in the light-mediated regulation of growth and development. However, their role in the thermosensory signaling pathway remains poorly understood. Here, we identified two B-BOX (BBX) proteins, BBX24 and BBX25, as novel components of the thermosensory pathway to promote warm temperature-mediated growth in Arabidopsis. The bbx24 and bbx25 single mutants showed moderate temperature insensitivity, while the bbx24bbx25 double mutants displayed strong temperature-insensitive hypocotyl and cotyledon growth. Warm temperatures induce BBX24 and BBX25 mRNA expression and protein accumulation. Genetic and biochemical analysis revealed that BBX24/BBX25 promotes thermomorphogenesis by stabilizing PHYTOCHROME INTERACTING FACTOR 4 (PIF4), a key component of the thermosensory pathway, probably through direct physical interaction. Interestingly, our study also revealed that the thermosensor EARLY FLOWERING 3 (ELF3), a potent inhibitor of PIF4 function, acts upstream of BBX24/BBX25, wherein ELF3 inhibits BBX24/BBX25 gene expression at low ambient temperatures in the evening. However, warm temperatures render ELF3 inactive, enhancing BBX24/BBX25 activity and stabilizing PIF4 protein and thermomorphogenic growth. Together, this study unravels ELF3/BBX24/BBX25-PIF4 as a key regulatory module that controls growth and development under varying temperature cues.
Score: 8.2, Published: 2024-02-09
DOI: 10.1101/2024.02.07.579300
Proper spatiotemporal distribution of the phytohormone auxin throughout plant tissues mediates a variety of developmental processes. Auxin levels are tightly regulated via de novo synthesis, transport, and conversion from its conjugated forms and precursors. These levels can be regulated through conversion of the auxin precursor, indole 3-butyric acid (IBA), into the active auxin, indole-3-acetic acid (IAA), in a peroxisomal {beta}-oxidation process. Defects in IBA-to-IAA conversion cause multiple developmental defects in Arabidopsis, demonstrating IBA-derived IAA is physiologically important to the active auxin pool. Similar to IAA, transport of IBA modulates development. However, the mechanisms governing transport of this molecule remain largely unknown. Here, we identify a mutation in the ABCC10 gene of Arabidopsis that suppresses the abcg36 hypersensitivity to IBA and its synthetic analog, 2,4-dichlorophenoxy butyric acid (2,4-DB) and the abcg36 hyperaccumulation of [3H]-IBA. We found that ABCC10 acts as a direct vacuolar transporter of IBA. Further, ABCC10 is necessary for proper development of the root apical meristem and leaf tissue. Our findings uncover a previously uncharacterized method of IBA transport that regulates aspects of plant development.