Lipid Signaling Requires ROS Production to Elicit Actin Cytoskeleton Remodeling during Plant Innate Immunity

Abstract

In terrestrial plants a basal innate immune system, pattern-triggered immunity (PTI), has evolved to limit infection by diverse microbes. The remodeling of actin cytoskeletal arrays is now recognized as a key hallmark event during the rapid host cellular responses to pathogen attack. Several actin binding proteins have been demonstrated to fine tune the dynamics of actin filaments during this process. However, the upstream signals that stimulate actin remodeling during PTI signaling remain poorly characterized. Two second messengers, reactive oxygen species (ROS) and phosphatidic acid (PA), are elevated following pathogen perception or microbe-associated molecular pattern (MAMP) treatment, and the timing of signaling fluxes roughly correlates with actin cytoskeletal rearrangements. Here, we combined genetic analysis, chemical complementation experiments, and quantitative live-cell imaging experiments to test the role of these second messengers in actin remodeling and to order the signaling events during plant immunity. We demonstrated that PHOSPHOLIPASE Dβ (PLDβ) isoforms are necessary to elicit actin accumulation in response to flg22-associated PTI. Further, bacterial growth experiments and MAMP-induced apoplastic ROS production measurements revealed that PLDβ-generated PA acts upstream of ROS signaling to trigger actin remodeling through inhibition of CAPPING PROTEIN (CP) activity. Collectively, our results provide compelling evidence that PLDβ/PA functions upstream of RBOHD-mediated ROS production to elicit actin rearrangements during the innate immune response in Arabidopsis.

ILEE: Algorithms and toolbox for unguided and accurate quantitative analysis of cytoskeletal images

“…Therefore, the global threshold identified through NNES and the estimation model is used in this study to define the coarse background area for downstream processing. Additionally, we further improved the 3D coarse background estimation model by introducing another published dataset ( Cao et al, 2022 ) with image augmentation for diverse ground noise pattern ( Fig. S3 ).…”

“…As the original training dataset of Fig. S2 may not have satisfactory variation of threshold-at-peak range, we introduced published actin image samples ( Cao et al, 2022 ) from a different microscope device in a different lab and applied image augmentation to generate a greatly diverse dataset for model training, resulting an enhanced 3D coarse thresholding model. (a) Scheme of datasets.…”

DIACYLGLYCEROL KINASE 5 participates in flagellin-induced signaling in Arabidopsis

“…Recently, another PA-producing enzyme, Arabidopsis PLDδ, was implicated in the plant reaction to chitin, a fungal PAMP ( Xing et al, 2019 ), suggesting the existence of non-redundant PA signaling pathways in plant immunity. Besides, in response to flg22, Arabidopsis PLDβs were shown to act upstream of ROS signaling to trigger actin remodeling through inhibition of CAPPING PROTEIN activity ( Cao et al, 2022 ).…”

The Cytoskeleton in Plant Immunity: Dynamics, Regulation, and Function

“…The levels of PA, a signal phospholipid, are increased during plant cell immune signal transduction [ 9 ]. Exogenous PA can increase the abundance of actin filaments in plant cells [ 4 ]. Hydrolysis of structural lipids such as phosphatidylcholine by phospholipase D (PLD) is one of the ways in which PA is produced and functions in plant immunity and cytoskeletal remodeling [ 9 ].…”

“…This is often accompanied by an increased intracellular calcium concentration, bursts of reactive oxygen species (ROS), accretion of the lipid molecule, activation of mitogen-activated protein kinases (MAPKs), etc. These messengers trigger downstream reactions and fine-tune cellular signaling networks in plant immunity [ 3 , 4 ]. However, many pathogens have adapted to this mechanism and evolved effectors to bypass or straightly repress PTI [ 5 ].…”