Protein S-acyl transferase 15 is involved in seed triacylglycerol catabolism during early seedling growth in Arabidopsis

Protein S-acylation, a new panacea for plant fitness

Protein S-acylation or palmitoylation is a reversible post-translational modification that influences many proteins encoded in plant genomes. Exciting progress in the past 3 years demonstrates that S-acylation modulates subcellular localization, interacting profiles, activity, or turnover of substrate proteins in plants, participating in developmental processes and responses to abiotic or biotic stresses. In this review, we summarize and discuss the role of S-acylation in the targeting of substrate proteins. We highlight complex roles of S-acylation in receptor signaling. We also point out that feedbacks of protein S-acyl transferase by signaling initiated from their substrate proteins may be a recurring theme. Finally, the reversibility of S-acylation makes it a rapid and efficient way to respond to environmental cues. Future efforts on exploring these important aspects of S-acylation will give a better understanding of how plants enhance their fitness under ever changing and often harsh environments.

The S-acylation cycle of transcription factor MtNAC80 influences cold stress responses in Medicago truncatula

S-acylation is a reversible post-translational modification catalyzed by protein S-acyltransferases (PATs), and acyl protein thioesterases (APTs) mediate de-S-acylation. Although many proteins are S-acylated, how the S-acylation cycle modulates specific biological functions in plants is poorly understood. In this study, we report that the S-acylation cycle of transcription factor MtNAC80 is involved in the Medicago truncatula cold stress response. Under normal conditions, MtNAC80 localized to membranes through MtPAT9-induced S-acylation. In contrast, under cold stress conditions, MtNAC80 translocated to the nucleus through de-S-acylation mediated by thioesterases such as MtAPT1. MtNAC80 functions in the nucleus by directly binding the promoter of the glutathione S-transferase gene MtGSTU1 and promoting its expression, which enables plants to survive under cold stress by removing excess malondialdehyde and H2O2. Our findings reveal an important function of the S-acylation cycle in plants and provide insight into stress response and tolerance mechanisms.

Arabidopsis protein S-acyl transferases positively mediate BR signaling through S-acylation of BSK1

Protein S-acyl transferases (PATs) catalyze S-acylation, a reversible post-translational modification critical for membrane association, trafficking, and stability of substrate proteins. Many plant proteins are potentially S-acylated but few have corresponding PATs identified. By using genomic editing, confocal imaging, pharmacological, genetic, and biochemical assays, we demonstrate that three Arabidopsis class C PATs positively regulate BR signaling through S-acylation of BRASSINOSTEROID-SIGNALING KINASE1 (BSK1). PAT19, PAT20, and PAT22 associate with the plasma membrane (PM) and the trans-Golgi network/early endosome (TGN/EE). Functional loss of all three genes results in a plethora of defects, indicative of reduced BR signaling and rescued by enhanced BR signaling. PAT19, PAT20, and PAT22 interact with BSK1 and are critical for the S-acylation of BSK1, and for BR signaling. The PM abundance of BSK1 was reduced by functional loss of PAT19, PAT20, and PAT22 whereas abolished by its S-acylation-deficient point mutations, suggesting a key role of S-acylation in its PM targeting. Finally, an active BR analog induces vacuolar trafficking and degradation of PAT19, PAT20, or PAT22, suggesting that the S-acylation of BSK1 by the three PATs serves as a negative feedback module in BR signaling.

PROTEIN S-ACYL TRANSFERASE 13/16 modulate disease resistance by S-acylation of the nucleotide binding, leucine-rich repeat protein R5L1 in Arabidopsis

Nucleotide binding, leucine-rich repeat (NB-LRR) proteins are critical for disease resistance in plants, while we do not know whether S-acylation of these proteins plays a role during bacterial infection. We identified 30 Arabidopsis mutants with mutations in NB-LRR encoding genes from the Nottingham Arabidopsis Stock Center and characterized their contribution to the plant immune response after inoculation with Pseudomonas syringae pv tomato DC3000 (Pst DC3000). Of the five mutants that were hyper-susceptible to the pathogen, three (R5L1, R5L2 and RPS5) proteins contain the conserved S-acylation site in the N-terminal coiled-coil (CC) domain. In wild-type (WT) Arabidopsis plants, R5L1 was transcriptionally activated upon pathogen infection, and R5L1 overexpression lines had enhanced resistance. Independent experiments indicated that R5L1 localized at the plasma membrane (PM) via S-acylation of its N-terminal CC domain, which was mediated by PROTEIN S-ACYL TRANSFERASE 13/16 (PAT13, PAT16). Modification of the S-acylation site reduced its affinity for binding the PM, with a consequent significant reduction in bacterial resistance. PM localization of R5L1 was significantly reduced in pat13 and pat16 mutants, similar to what was found for WT plants treated with 2-bromopalmitate, an S-acylation-blocking agent. Transgenic plants expressing R5L1 in the pat13 pat16 double mutant showed no enhanced disease resistance. Overexpression of R5L1 in WT Arabidopsis resulted in substantial accumulation of reactive oxygen species after inoculation with Pst DC3000; this effect was not observed with a mutant R5L1 carrying a mutated S-acylation site. Our data suggest that PAT13- and PAT16-mediated S-acylation of R5L1 is crucial for its membrane localization to activate the plant defense response.

Protein S-acyltransferases and acyl protein thioesterases, regulation executors of protein S-acylation in plants

Protein S-acylation, also known as palmitoylation, is an important lipid post-translational modification of proteins in eukaryotes. S-acylation plays critical roles in a variety of protein functions involved in plant development and responses to abiotic and biotic stresses. The status of S-acylation on proteins is dynamic and reversible, which is catalyzed by protein S-acyltransferases (PATs) and reversed by acyl protein thioesterases. The cycle of S-acylation and de-S-acylation provides a molecular mechanism for membrane-associated proteins to undergo cycling and trafficking between different cell compartments and thus works as a switch to initiate or terminate particular signaling transductions on the membrane surface. In plants, thousands of proteins have been identified to be S-acylated through proteomics. Many S-acylated proteins and quite a few PAT-substrate pairs have been functionally characterized. A recently characterized acyl protein thioesterases family, ABAPT family proteins in Arabidopsis, has provided new insights into the de-S-acylation process. However, our understanding of the regulatory mechanisms controlling the S-acylation and de-S-acylation process is surprisingly incomplete. In this review, we discuss how protein S-acylation level is regulated with the focus on catalyzing enzymes in plants. We also propose the challenges and potential developments for the understanding of the regulatory mechanisms controlling protein S-acylation in plants.

Genome-Wide Identification of Genes Encoding for Rho-Related Proteins in 'Duli' Pear (Pyrus betulifolia Bunge) and Their Expression Analysis in Response to Abiotic Stress

Twelve Rho-related proteins (ROPs), namely PbROPs, were identified from the genome of the recently sequenced 'Duli' pear (Pyrus betulifolia Bunge), a wild-type pear variety routinely used for rootstocks in grafting in China. The length and molecular weight of these proteins are between 175 and 215 amino acids and 19.46 and 23.45 kDa, respectively. The 12 PbROPs are distributed on 8 of the 17 chromosomes, where chromosome 15 has the highest number of 3 PbROPs. Analysis of the deduced protein sequences showed that they are relatively conserved and all have the G domain, insertion sequence, and HVR motif. The expression profiles were monitored by quantitative RT-PCR, which showed that these 12 PbROP genes were ubiquitously expressed, indicating their involvement in growth and development throughout the life cycle of 'Duli' pear. However, they were altered upon treatments with abscisic acid (ABA, mimicking abiotic stress), polyethylene glycol (PEG, mimicking drought), and sodium chloride (NaCl, mimicking salt) to tissue-cultured seedlings. Further, transgenic Arabidopsis expressing PbROP1, PbROP2, and PbROP9 exhibited enhanced sensitivity to ABA, demonstrating that these 3 PbROPs may play important roles in the abiotic stress of 'Duli' pear. The combined results showed that the 'Duli' genome encodes 12 typical ROPs and they appeared to play important roles in growth, development, and abiotic stress. These preliminary data may guide future research into the molecular mechanisms of these 12 PbROPs and their utility in molecular breeding for abiotic stress-resistant 'Duli' pear rootstocks.

Screening DHHCs of S-acylated proteins using an OsDHHC cDNA library and bimolecular fluorescence complementation in rice

S-acylation is an important lipid modification that primarily involves DHHC proteins (DHHCs) and associated S-acylated proteins. No DHHC-S-acylated protein pair has been reported so far in rice (Oryza sativa L.) and the molecular mechanisms underlying S-acylation in plants are largely unknown. We constructed an OsDHHC cDNA library for screening corresponding pairs of DHHCs and S-acylated proteins using bimolecular fluorescence complementation assays. Five DHHC-S-acylated protein pairs (OsDHHC30-OsCBL2, OsDHHC30-OsCBL3, OsDHHC18-OsNOA1, OsDHHC13-OsNAC9, and OsDHHC14-GSD1) were identified in rice. Among the pairs, OsCBL2 and OsCBL3 were S-acylated by OsDHHC30 in yeast and rice. The localization of OsCBL2 and OsCBL3 in the endomembrane depended on S-acylation mediated by OsDHHC30. Meanwhile, all four OsDHHCs screened complemented the thermosensitive phenotype of an akr1 yeast mutant, and their DHHC motifs were required for S-acyltransferase activity. Overexpression of OsDHHC30 in rice plants improved their salt and oxidative tolerance. Together, these results contribute to our understanding of the molecular mechanism underlying S-acylation in plants.

S-acylation of P2K1 mediates extracellular ATP-induced immune signaling in Arabidopsis

S-acylation is a reversible protein post-translational modification mediated by protein S-acyltransferases (PATs). How S-acylation regulates plant innate immunity is our main concern. Here, we show that the plant immune receptor P2K1 (DORN1, LecRK-I.9; extracellular ATP receptor) directly interacts with and phosphorylates Arabidopsis PAT5 and PAT9 to stimulate their S-acyltransferase activity. This leads, in a time-dependent manner, to greater S-acylation of P2K1, which dampens the immune response. pat5 and pat9 mutants have an elevated extracellular ATP-induced immune response, limited bacterial invasion, increased phosphorylation and decreased degradation of P2K1 during immune signaling. Mutation of S-acylated cysteine residues in P2K1 results in a similar phenotype. Our study reveals that S-acylation effects the temporal dynamics of P2K1 receptor activity, through autophosphorylation and protein degradation, suggesting an important role for this modification in regulating the ability of plants in respond to external stimuli.

S-acylation in plants: an expanding field

S-acylation is a common yet poorly understood fatty acid-based post-translational modification of proteins in all eukaryotes, including plants. While exact roles for S-acylation in protein function are largely unknown the reversibility of S-acylation indicates that it is likely able to play a regulatory role. As more studies reveal the roles of S-acylation within the cell it is becoming apparent that how S-acylation affects proteins is conceptually different from other reversible modifications such as phosphorylation or ubiquitination; a new mind-set is therefore required to fully integrate these data into our knowledge of plant biology. This review aims to highlight recent advances made in the function and enzymology of S-acylation in plants, highlights current and emerging technologies for its study and suggests future avenues for investigation.

Knockout of the S-acyltransferase Gene, PbPAT14, Confers the Dwarf Yellowing Phenotype in First Generation Pear by ABA Accumulation

The development of dwarf fruit trees with smaller and compact characteristics leads to significantly increased fruit production, which is a major objective of pear (Pyrus bretschneideri) breeding. We identified the S-acylation activity of PbPAT14, an S-acyltransferase gene related to plant development, using a yeast (Saccharomyces cerevisiae) complementation assay, and also PbPAT14 could rescue the growth defect of the Arabidopsis mutant atpat14. We further studied the function of PbPAT14 by designing three guide RNAs for PbPAT14 to use in the CRISPR/Cas9 system. We obtained 22 positive transgenic pear lines via Agrobacterium-mediated transformation using cotyledons from seeds of Pyrus betulifolia (‘Duli’). Six of these lines exhibited the dwarf yellowing phenotype and were homozygous mutations according to sequencing analysis. Ultrastructure analysis suggested that this dwarfism was manifested by shorter, thinner stems due to a reduction in cell number. A higher level of endogenous abscisic acid (ABA) and a higher transcript level of the ABA pathway genes in the mutant lines revealed that the PbPAT14 function was related to the ABA pathway. Overall, our experimental results increase the understanding of how PATs function in plants and help elucidate the mechanism of plant dwarfism.