VIP1, a bZIP protein, interacts with the catalytic subunit of protein phosphatase 2A in Arabidopsis thaliana

Dephosphorylation of bZIP59 by PP2A ensures appropriate shade avoidance response in Arabidopsis

Changes in light quality and quantity experienced by many shade-intolerant plants grown in close proximity lead to transcriptional reprogramming and shade avoidance syndrome (SAS). Despite the importance of phosphorylation-dependent signaling in cellular physiology, phosphorylation events during SAS are largely unknown. Here, we examined shade-regulated phosphorylation events in Arabidopsis using quantitative phosphoproteomics. We confirmed shade-induced dephosphorylation of bZIP59, a basic region/leucine zipper motif (bZIP) transcription factor. Shade treatment promotes the nuclear localization of bZIP59, which can be mimicked by mutation of the phosphorylation sites on bZIP59. Phenotypic analysis identified that bZIP59 negatively regulated shade-induced hypocotyl elongation. bZIP59 repressed the shade-induced activation of certain growth-related genes, while shade increased the DNA binding of bZIP59. Furthermore, the protein phosphatase 2A (PP2A) mediated dephosphorylation of bZIP59. Our study characterized a previously unidentified mechanism by which the phytochrome B (phyB)-PP2A-bZIP59 regulatory module integrates shade signals and transcriptomes, broadening our knowledge of phosphorylation strategies for rapid adaptation to shade.

VIP1 and its close homologs confer mechanical stress tolerance in Arabidopsis leaves

VIP1, an Arabidopsis thaliana basic leucine zipper transcription factor, and its close homologs are imported from the cytoplasm to the nucleus when cells are exposed to mechanical stress. They bind to AGCTG (G/T) and regulate mechanical stress responses in roots. However, their role in leaves is unclear. To clarify this, mutant lines (QM1 and QM2) that lack the functions of VIP1 and its close homologs (bZIP29, bZIP30 and PosF21) were generated. Brushing more severely damaged QM1 and QM2 leaves than wild-type leaves. Genes regulating stress responses and cell wall properties were downregulated in brushed QM2 leaves and upregulated in brushed VIP1-GFP-overexpressing (VIP1-GFPox) leaves compared to wild-type leaves in a transcriptome analysis. The VIP1-binding sequence AGCTG (G/T) was enriched in the promoters of genes downregulated in brushed QM2 leaves compared to wild-type leaves and in those upregulated in brushed VIP1-GFPox leaves. Calmodulin-binding transcription activators (CAMTAs) are known regulators of mechanical stress responses, and the CAMTA-binding sequence CGCGT was enriched in the promoters of genes upregulated in the brushed QM2 leaves and in those downregulated in the brushed VIP1-GFPox leaves. These findings suggest that VIP1 and its homologs upregulate genes via AGCTG (G/T) and influence CAMTA-dependent gene expression to enhance mechanical stress tolerance in leaves.

Walnut phosphatase 2A proteins interact with basic leucine zipper protein JrVIP1 to regulate osmotic stress response via calcium signaling

Walnut is an important economic tree species that is susceptible to osmotic stress. Scientific cultivation management is an important way to improve the yield and quality of walnuts, which requires understanding the regulatory mechanisms in response to osmotic stress. Therefore, in this study, 15 protein phosphatase 2A (PP2A) genes were identified from the walnut transcriptome (named JrPP2A01~15) and their potential function responses to osmotic stress were elucidated. The open reading frame (ORF) of JrPP2A01~15 ranges from 651 to 1,764 bp in length, the molecular weight of the encoded proteins are 24.15-65.61 kDa, and the theoretical isoelectric points are 4.80-8.37. These JrPP2As were unevenly distributed on 10 chromosomes and divided into five groups based on the composition of conserved domains, motifs, and exon/intron organizations. The five groups are JrPP2AAs, JrPP2AB's, JrPP2AB''s, JrPP2AB55s, and JrPP2ACs, including 1, 5, 2, 3, and 4 members, accordingly. The cis-elements in JrPP2As' promoters were involved in responses to hormone and abiotic stress. Most JrPP2A genes, excluding JrPP2A01, JrPP2A02, JrPP2A05, JrPP2A06, and JrPP2A13, could be induced significantly by PEG6000, NaCl, CaCl2 and ABA. JrPP2A02, JrPP2A05, JrPP2A07, JrPP2A09, and JrPP2A14, could independently interact with a bZIP transcription factor JrVIP1. Moreover, overexpression of JrPP2A07, JrPP2A09, and JrPP2A14 could significantly decrease ROS accumulation while increasing calcium (Ca) uptake exposed to PEG6000 and NaCl stresses, which was mediated by exogenous CaCl2 and ABA. These results suggested that JrPP2A genes play potential key roles in walnut response to drought and salt-inducing osmotic stress involving Ca- and ABA-dependent signaling pathways.

GmbZIP152, a Soybean bZIP Transcription Factor, Confers Multiple Biotic and Abiotic Stress Responses in Plant

Soybean is one of the most important food crops in the world. However, with the environmental change in recent years, many environmental factors like drought, salinity, heavy metal, and disease seriously affected the growth and development of soybean, causing substantial economic losses. In this study, we screened a bZIP transcription factor gene, GmbZIP152, which is significantly induced by Sclerotinia sclerotiorum (S. sclerotiorum), phytohormones, salt-, drought-, and heavy metal stresses in soybean. We found that overexpression of GmbZIP152 in Arabidopsis (OE-GmbZIP152) enhances the resistance to S. sclerotiorum and the tolerance of salt, drought, and heavy metal stresses compared to wild-type (WT). The antioxidant enzyme related genes (including AtCAT1, AtSOD, and AtPOD1) and their enzyme activities are induced by S. sclerotiorum, salt, drought, and heavy metal stress in OE-GmbZIP152 compared to WT. Furthermore, we also found that the expression level of biotic- and abiotic-related marker genes (AtLOX6, AtACS6, AtERF1, and AtABI2, etc.) were increased in OE-GmbZIP152 compared to WT under S. sclerotiorum and abiotic stresses. Moreover, we performed a Chromatin immunoprecipitation (ChIP) assay and found that GmbZIP152 could directly bind to promoters of ABA-, JA-, ETH-, and SA-induced biotic- and abiotic-related genes in soybean. Altogether, GmbZIP152 plays an essential role in soybean response to biotic and abiotic stresses.

The necrosis- and ethylene-inducing peptide 1-like protein (NLP) gene family of the plant pathogen Corynespora cassiicola

Effectors are secreted by plant-associated microorganisms to modify the host cell physiology. As effectors, the Necrosis- and Ethylene-inducing peptide 1-like proteins (NLPs) are involded in the early phases of plant infection and may trigger host immune responses. Corynespora cassiicola is a polyphagous plant pathogen that causes target spot on many agriculturally important crops. Using genome assembly, gene prediction, and proteome annotation tools, we retrieved 135 NLP-encoding genes from proteomes of 44 isolates. We explored the evolutionary history of NLPs using Bayesian phylogeny, gene genealogies, and selection analyses. We accessed the expression profiles of the NLP genes during the early phase of C. cassiicola-soybean interaction. Three NLP putative-effector genes (Cc_NLP1.1, Cc_NLP1.2A, and Cc_NLP1.2B) were maintained in the genomes of all isolates tested. An NLP putative-non-effector gene (Cc_NLP1.3) was found in three isolates that had been originally obtained from soybean. Putative-effector NLPs were under different selective constraints: Cc_NLP1.1 was under stronger selective pressure, while Cc_NLP1.2A was under a more relaxed constraint. Meanwhile, Cc_NLP1.2B likely evolved under either positive or balancing selection. Despite highly divergent, the putative-effector NLPs maintain conserved the residues necessary to trigger plant immune responses, suggesting they are potentially functional. Only the Cc_NLP1.1 putative-effector gene was significantly expressed at the early hours of soybean colonization, while Cc_NLP1.2A and Cc_NLP1.2B showed much lower levels of gene expression.

The B″-family subunits of protein phosphatase 2A are necessary for in-vitro dephosphorylation of the Arabidopsis mechanosensory transcription factor VIP1

Protein phosphatase 2A (PP2A) B″-family subunits have Ca²⁺-binding EF-hand motifs and can bind PP2A substrates. Arabidopsis thaliana PP2A B″-family subunits are encoded by six genes, and bind a transcription factor, VIP1. VIP1 is dephosphorylated and nuclear-localized by hypo-osmotic stress. However, whether PP2A B″-family subunits mediate the VIP1 dephosphorylation is unclear. Here, we show by yeast two-hybrid and in vitro pull down assays that Arabidopsis PP2A B″-family subunits bind Arabidopsis PP2A A (scaffold) subunits. We also show that VIP1 dephosphorylation in vitro can be induced by a PP2A B″-family subunit.