Perfluorooctanesulfonic Acid Alters the Plant's Phosphate Transport Gene Network and Exhibits Antagonistic Effects on the Phosphate Uptake.

Per- and polyfluoroalkyl substances (PFASs), with significant health risks to humans and wildlife, bioaccumulate in plants. However, the mechanisms underlying plant uptake remain poorly understood. This study deployed transcriptomic analysis coupled with genetic and physiological studies using Arabidopsis to investigate how plants respond to perfluorooctanesulfonic acid (PFOS), a long-chain PFAS. We observed increased expressions of genes involved in plant uptake and transport of phosphorus, an essential plant nutrient, suggesting intertwined uptake and transport processes of phosphorus and PFOS. Furthermore, PFOS-altered response differed from the phosphorus deficiency response, disrupting phosphorus metabolism to increase phosphate transporter (PHT) transcript. Interestingly, pht1;2 and pht1;8 mutants showed reduced sensitivity to PFOS compared to that of the wild type, implying an important role of phosphate transporters in PFOS sensing. Furthermore, PFOS accumulated less in the shoots of the pht1;8 mutant, indicating the involvement of PHT1;8 protein in translocating PFOS from roots to shoots. Supplementing phosphate improved plant's tolerance to PFOS and reduced PFOS uptake, suggesting that manipulating the phosphate source in PFOS-contaminated soils may be a promising strategy for minimizing PFOS uptake by edible crops or promoting PFOS uptake during phytoremediation. This study highlighted the critical role of phosphate sensing and transport system in the uptake and translocation of PFOS in plants.

Noncanonical mono(ADP-ribosyl)ation of zinc finger SZF proteins counteracts ubiquitination for protein homeostasis in plant immunity.

Protein ADP-ribosylation is a reversible post-translational modification that transfers ADP-ribose from NAD+ onto acceptor proteins. Poly(ADP-ribosyl)ation (PARylation), catalyzed by poly(ADP-ribose) polymerases (PARPs) and poly(ADP-ribose) glycohydrolases (PARGs), which remove the modification, regulates diverse cellular processes. However, the chemistry and physiological functions of mono(ADP-ribosyl)ation (MARylation) remain elusive. Here, we report that Arabidopsis zinc finger proteins SZF1 and SZF2, key regulators of immune gene expression, are MARylated by the noncanonical ADP-ribosyltransferase SRO2. Immune elicitation promotes MARylation of SZF1/SZF2 via dissociation from PARG1, which has an unconventional activity in hydrolyzing both poly(ADP-ribose) and mono(ADP-ribose) from acceptor proteins. MARylation antagonizes polyubiquitination of SZF1 mediated by the SH3 domain-containing proteins SH3P1/SH3P2, thereby stabilizing SZF1 proteins. Our study uncovers a noncanonical ADP-ribosyltransferase mediating MARylation of immune regulators and underpins the molecular mechanism of maintaining protein homeostasis by the counter-regulation of ADP-ribosylation and polyubiquitination to ensure proper immune responses.

A nonproteinaceous Fusarium cell wall extract triggers receptor-like protein-dependent immune responses in Arabidopsis and cotton.

Fusarium wilt caused by the ascomycete fungus Fusarium oxysporum is a devastating disease of many economically important crops. The mechanisms underlying plant responses to F. oxysporum infections remain largely unknown. We demonstrate here that a water-soluble, heat-resistant and nonproteinaceous F. oxysporum cell wall extract (FoCWE) component from multiple F. oxysporum isolates functions as a race-nonspecific elicitor, also termed pathogen-associated molecular pattern (PAMP). FoCWE triggers several demonstrated immune responses, including mitogen-activated protein (MAP) kinase phosphorylation, reactive oxygen species (ROS) burst, ethylene production, and stomatal closure, in cotton and Arabidopsis. Pretreated FoCWE protects cotton seeds against infections by virulent F. oxysporum f. sp. vasinfectum (Fov), and Arabidopsis plants against the virulent bacterium, Pseudomonas syringae, suggesting the potential application of FoCWEs in crop protection. Host-mediated responses to FoCWE do not appear to require LYKs/CERK1, BAK1 or SOBIR1, which are commonly involved in PAMP perception and/or signalling. However, FoCWE responses and Fusarium resistance in cotton partially require two receptor-like proteins, GhRLP20 and GhRLP31. Transcriptome analysis suggests that FoCWE preferentially activates cell wall-mediated defence, and Fov has evolved virulence mechanisms to suppress FoCWE-induced defence. These findings suggest that FoCWE is a classical PAMP that is potentially recognised by a novel pattern-recognition receptor to regulate cotton resistance to Fusarium infections.

The Pseudomonas syringae pv. tomato DC3000 type III effector HopF2 has a putative myristoylation site required for its avirulence and virulence functions.

The HopPtoF locus in Pseudomonas syringae pv. tomato DC3000 harbors two genes, ShcF and HopF2 (previously named ShcF(Pto) and HopF(Pto)), that encode a type III chaperone and a cognate effector protein, respectively. The HopF2 gene has a rare initiation codon, ATA that was reported to be functional only in mitochondrial genes. Here, we report that the native HopPtoF locus of DC3000 confers an avirulence function in tobacco W38 plants, indicating that the ATA start codon directs the synthesis of a functional effector. However, disruption of HopF2 in DC3000 genome did not alter the bacterial virulence in tomato plants. The HopPtoF locus displayed a measurable virulence activity in two strains of P. syringae pv. tomato when the ATA start codon was changed to ATG, and this change also elevated the avirulence function in W38 plants. HopF2 contains a putative myristoylation site. Mutational analysis indicated that this site is required for plasma membrane localization and virulence and avirulence activities of HopF2.