Biology subjects

DeFalco, T. A.

Publications and source records attributed to DeFalco, T. A..

7 recordsLinked to original sources

bioRxiv2026

The Arabidopsis outward K+ channel GORK mediates flg22-induced K+ efflux and stomatal closure

Transient K+ efflux occurs rapidly following pathogen-associated molecular pattern (PAMP) perception by pattern recognition receptors (PRRs) as part of pattern-triggered immunity (PTI). However, the molecular identities of the K+ channels responsible for PTI-associated K+ efflux and the mechanisms linking immune signaling to K+ channel regulation remain largely unknown. Here, we show that the channel GUARD CELL OUTWARD RECTIFYING K+ (GORK) is required for K+ efflux and stomatal closure induced by flg22, a model PAMP derived from bacterial flagellin. BOTRYTIS-INDUCED KINASE 1 (BIK1), a receptor-like cytoplasmic kinase associated with immune receptor complexes that functions as a central regulator of PTI, interacts with GORK and phosphorylates the channel on the conserved T199 residue in vitro. Electrophysiological analyses indicate that BIK1 inhibits GORK activity in a kinase-dependent manner and that T199 plays an essential role for GORK function. Together, this study identifies GORK as the key K+ channel executing rapid PTI-associated K+ efflux and associated stomatal closure, thus shedding light on the mechanisms of early immune signaling.

plant biology↗

bioRxiv2025

New alleles of Arabidopsis BIK1 reinforce its predominant role in pattern-triggered immunity and caution interpretations of other reported functions

The receptor-like cytoplasmic kinase BIK1 and its close homolog PBL1 have been widely recognized as central components of plant immunity. However, most genetic studies of BIK1 and PBL1 functions were carried out with single T-DNA insertional mutant alleles. Some phenotypes observed in these mutants, e.g. autoimmunity, have been difficult to reconcile with the proposed role of BIK1 and PBL1 in pattern-triggered immunity. In this study, we generated multiple new alleles of bik1 and pbl1 by CRISPR-Cas9-based gene editing and systematically analyzed these mutants alongside existing T-DNA insertional lines. These analyses reinforced the central role of BIK1 and PBL1 in pattern-triggered immunity mediated by both receptor kinases and receptor-like proteins. At the same time, however, we revealed several pleiotropic phenotypes associated with T-DNA insertions that are not necessarily linked to loss of BIK1 or PBL1 function. Further analyses of newly generated bik1 pbl1 double mutants uncovered an even greater contribution of these kinases to immune signaling and disease resistance than previously appreciated. These findings clarify longstanding ambiguities surrounding BIK1 and PBL1 functions.

plant biology↗

bioRxiv2024

Conservation of an immune homeostasis module in land plants

Calcium-dependent protein kinases (CDPKs) decode cellular calcium transients and play diverse roles in plant growth and stress responses, including immunity. In Arabidopsis thaliana (At, Arabidopsis thereafter), AtCPK28 contributes to immune homeostasis by phosphorylating subgroup IV plant U-box proteins AtPUB22/24/25/26, which target the key immune receptor-like cytoplasmic kinase (RLCK) AtBIK1 for turnover. While this module is conserved in multiple angiosperms, it is unclear if the role of CPK28 in immune homeostasis is conserved more broadly across land plants. Here, we took an evolutionary comparative approach to understand the role of CPK28. We identified a single CPK28 ortholog in the liverwort Marchantia polymorpha, MpCPK28, which exhibits Ca2+-dependent kinase activity that is inhibited by calmodulin in vitro. We identified the subgroup IV plant U-box protein MpPUB20e as a substrate of MpCPK28. MpPUB20e is able to ubiquitinate MpPBLa, the functional ortholog of AtBIK1. We also provide preliminary evidence that MpPBLa undergoes proteasomal degradation in Marchantia, suggesting that optimization of MpPBLa protein accumulation is conserved across land plants. Interestingly, while loss of CPK28 function in multiple angiosperm species results in enhanced immune signaling, we find that Marchantia Mpcpk28 mutant alleles do not display enhanced immune-triggered production of reactive oxygen species or resistance to two pathogens. However, transgenic expression of MpCPK28 was able to restore function in Arabidopsis cpk28-1 mutants, suggesting latent functional conservation of MpCPK28. Furthermore, while AtCPK28-mediated phosphorylation of Thr95/94 on AtPUB25/26 is known to contribute to their activation, we could not observe a functional role for the equivalent residue Thr122 on MpPUB20e. Taken together, our results suggest that post-translational fine-tuning by CPK28 is likely to have refined the PUB-BIK1 module in the vascular plant lineages.

plant biology↗

bioRxiv2024

Arabidopsis WALL-ASSOCIATED KINASES are not required for oligogalacturonide-induced signaling and immunity

Carbohydrate-based cell wall signaling impacts plant growth, development, and stress responses; however, how cell wall signals are perceived and transduced remains poorly understood. Several cell wall breakdown products have been described as typical damage-associated molecular patterns (DAMPs) that activate plant immunity, including pectin-derived oligogalacturonides (OGs). Receptor kinases (RKs) of the WALL-ASSOCIATED KINASE (WAK) family have been shown to bind pectin and OGs, and were previously proposed as OG receptors. However, unambiguous genetic evidence for the role of WAKs in OG responses is lacking. Here, we investigated the role of Arabidopsis WAKs in OG perception using a novel deletion mutant of the clustered WAK family. Using a combination of immune assays for early and late pattern-triggered immunity (PTI), we show that WAKs are dispensable for OG-induced signaling and immunity, indicating that they are not bona fide OG receptors.

plant biology↗

bioRxiv2021

A conserved regulatory module regulates receptor kinase signaling in immunity and development

Ligand recognition by cell-surface receptors underlies development and immunity in both animals and plants. Modulating receptor signaling is critical for appropriate cellular responses but the mechanisms ensuring this are poorly understood. Here, we show that signaling by plant receptors for pathogen-associated molecular patterns (PAMPs) in immunity and CLAVATA3/EMBRYO SURROUNDING REGION-RELATED peptides (CLEp) in development employ a similar regulatory module. In the absence of ligand, signaling is dampened through association with specific type-2C protein phosphatases (PP2Cs). Upon activation, PAMP and CLEp receptors phosphorylate divergent cytosolic kinases, which, in turn, phosphorylate the phosphatases, thereby promoting their release from the receptor complexes. Our work reveals a regulatory circuit shared between immune and developmental receptor signaling, which may have broader important implications for plant receptor kinase-mediated signaling in general.

plant biology↗

bioRxiv2020

Conserved Molecular Function and Regulatory Subfunctionalization of the LORELEI Gene Family in Brassicaceae

A signaling complex comprising members of the LORELEI (LRE)-LIKE GPI-anchored protein (LLG) and Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE (CrRLK1L) families perceive RAPID ALKALINIZATION FACTOR (RALF) peptides and regulate growth, reproduction, immunity, and stress responses in Arabidopsis. Genes encoding these proteins are members of multi-gene families in most angiosperms and could generate thousands of signaling complex variants. However, the link(s) between expansion of these gene families and the functional diversification of this critical signaling complex as well as the evolutionary factors underlying the maintenance of gene duplicates remain unknown. Here, we investigated LLG gene family evolution, function, and expression in angiosperms. We found that LLGs in monocots and eudicots are descendants of a duplication early in angiosperm evolution and that both ancient and recent LLG duplicates are retained. Complementation and expression analysis showed that expression divergence of LLGs (regulatory subfunctionalization), rather than functional divergence, explains the retention of paralogs in Brassicales. All but one extant monocot and eudicot species examined maintained an LLG copy with preferential expression in male reproductive tissues, with the other duplicate copies showed highest levels of expression in female or vegetative tissues. Interestingly, the single LLG copy in Amborella (sister to all other angiosperms) is expressed vastly higher in male compared to female reproductive or vegetative tissues. Reconstruction of expression evolution showed that the highest inferred expression levels for the single copy ancestral angiosperm LLG was in male reproductive tissues. We propose that expression divergence played an important role in maintenance of LLG duplicates in angiosperms. One Sentence SummaryExpression divergence played an important role in maintenance of two sub-groups of LLG duplicates in angiosperms

plant biology↗

bioRxiv2018

CrRLK1L receptor-like kinases HERK1 and ANJEA are female determinants of pollen tube reception

Communication between the gametophytes is vital for angiosperm fertilisation. Multiple CrRLK1L-type receptor kinases prevent premature pollen tube burst, while another CrRLK1L protein, FERONIA (FER), is required for pollen tube burst in the female gametophyte. We report here the identification of two additional CrRLK1L homologues, HERCULES RECEPTOR KINASE 1 (HERK1) and ANJEA (ANJ), which act redundantly to promote pollen tube burst at the synergid cells. HERK1 and ANJ localise to the filiform apparatus of the synergid cells in unfertilised ovules, and in herk1 anj mutants a majority of ovules remain unfertilised due to pollen tube overgrowth, together indicating that HERK1 and ANJ act as female determinants for fertilisation. As in fer mutants, the synergid cell-specific, endomembrane protein NORTIA (NTA) is not relocalised after pollen tube reception; however, unlike fer mutants, reactive oxygen species levels are unaffected in herk1 anj double mutants. Both ANJ and HERK1 associate with FER and its proposed co-receptor LORELEI (LRE) in planta. Together, our data indicate that HERK1 and ANJ act with FER to mediate female-male gametophyte interactions during plant fertilisation.

genetics↗