Visualization of a curated Oryza sativa L. CDPKs Protein-Protein Interaction Network (CDPK-OsPPIN).

Calcium-Dependent Protein Kinases (CDPKs) translate calcium ion (Ca2+) signals into direct phosphorylation of proteins involved in stress response and plant growth. To get a clear picture of CDPKs functions, we must identify and explore the CDPKs targets and their respective roles in plant physiology. Here, we present a manually curated Oryza sativa L. CDPK Protein-Protein Interaction Network (CDPK-OsPPIN). The CDPK-OsPPIN provides an interactive graphical tool to assist hypothesis generation by researchers investigating CDPK roles and functional diversity.

The sugar-responsive circadian clock regulator bZIP63 modulates plant growth.

Adjustment to energy starvation is crucial to ensure growth and survival. In Arabidopsis thaliana (Arabidopsis), this process relies in part on the phosphorylation of the circadian clock regulator bZIP63 by SUCROSE non-fermenting RELATED KINASE1 (SnRK1), a key mediator of responses to low energy. We investigated the effects of mutations in bZIP63 on plant carbon (C) metabolism and growth. Results from phenotypic, transcriptomic and metabolomic analysis of bZIP63 mutants prompted us to investigate the starch accumulation pattern and the expression of genes involved in starch degradation and in the circadian oscillator. bZIP63 mutation impairs growth under light-dark cycles, but not under constant light. The reduced growth likely results from the accentuated C depletion towards the end of the night, which is caused by the accelerated starch degradation of bZIP63 mutants. The diel expression pattern of bZIP63 is dictated by both the circadian clock and energy levels, which could determine the changes in the circadian expression of clock and starch metabolic genes observed in bZIP63 mutants. We conclude that bZIP63 composes a regulatory interface between the metabolic and circadian control of starch breakdown to optimize C usage and plant growth.

Carbon/nitrogen metabolism and stress response networks - calcium-dependent protein kinases as the missing link?

Calcium-dependent protein kinases (CDPKs) play essential roles in plant development and stress responses. CDPKs have a conserved kinase domain, followed by an auto-inhibitory junction connected to the calmodulin-like domain that binds Ca2+. These structural features allow CDPKs to decode the dynamic changes in cytoplasmic Ca2+ concentrations triggered by hormones and by biotic and abiotic stresses. In response to these signals, CDPKs phosphorylate downstream protein targets to regulate growth and stress responses according to the environmental and developmental circumstances. The latest advances in our understanding of the metabolic, transcriptional, and protein-protein interaction networks involving CDPKs suggest that they have a direct influence on plant carbon/nitrogen (C/N) balance. In this review, we discuss how CDPKs could be key signaling nodes connecting stress responses with metabolic homeostasis, and acting together with the sugar and nutrient signaling hubs SnRK1, HXK1, and TOR to improve plant fitness.

Turning the Knobs: The Impact of Post-translational Modifications on Carbon Metabolism.

Plants rely on the carbon fixed by photosynthesis into sugars to grow and reproduce. However, plants often face non-ideal conditions caused by biotic and abiotic stresses. These constraints impose challenges to managing sugars, the most valuable plant asset. Hence, the precise management of sugars is crucial to avoid starvation under adverse conditions and sustain growth. This review explores the role of post-translational modifications (PTMs) in the modulation of carbon metabolism. PTMs consist of chemical modifications of proteins that change protein properties, including protein-protein interaction preferences, enzymatic activity, stability, and subcellular localization. We provide a holistic view of how PTMs tune resource distribution among different physiological processes to optimize plant fitness.

JAZ4 is involved in plant defense, growth, and development in Arabidopsis.

Jasmonate zim-domain (JAZ) proteins comprise a family of transcriptional repressors that modulate jasmonate (JA) responses. JAZ proteins form a co-receptor complex with the F-box protein coronatine insensitive1 (COI1) that recognizes both jasmonoyl-l-isoleucine (JA-Ile) and the bacterial-produced phytotoxin coronatine (COR). Although several JAZ family members have been placed in this pathway, the role of JAZ4 in this model remains elusive. In this study, we observed that the jaz4-1 mutant of Arabidopsis is hyper-susceptible to Pseudomonas syringae pv. tomato (Pst) DC3000, while Arabidopsis lines overexpressing a JAZ4 protein lacking the Jas domain (JAZ4∆Jas) have enhanced resistance to this bacterium. Our results show that the Jas domain of JAZ4 is required for its physical interaction with COI1, MYC2 or MYC3, but not with the repressor complex adaptor protein NINJA. Furthermore, JAZ4 degradation is induced by COR in a proteasome- and Jas domain-dependent manner. Phenotypic evaluations revealed that expression of JAZ4∆Jas results in early flowering and increased length of root, hypocotyl, and petiole when compared with Col-0 and jaz4-1 plants, although JAZ4∆Jas lines remain sensitive to MeJA- and COR-induced root and hypocotyl growth inhibition. Additionally, jaz4-1 mutant plants have increased anthocyanin accumulation and late flowering compared with Col-0, while JAZ4∆Jas lines showed no alteration in anthocyanin production. These findings suggest that JAZ4 participates in the canonical JA signaling pathway leading to plant defense response in addition to COI1/MYC-independent functions in plant growth and development, supporting the notion that JAZ4-mediated signaling may have distinct branches.

Circadian Entrainment in Arabidopsis by the Sugar-Responsive Transcription Factor bZIP63.

Synchronization of circadian clocks to the day-night cycle ensures the correct timing of biological events. This entrainment process is essential to ensure that the phase of the circadian oscillator is synchronized with daily events within the environment [1], to permit accurate anticipation of environmental changes [2, 3]. Entrainment in plants requires phase changes in the circadian oscillator, through unidentified pathways, which alter circadian oscillator gene expression in response to light, temperature, and sugars [4-6]. To determine how circadian clocks respond to metabolic rhythms, we investigated the mechanisms by which sugars adjust the circadian phase in Arabidopsis [5]. We focused upon metabolic regulation because interactions occur between circadian oscillators and metabolism in several experimental systems [5, 7-9], but the molecular mechanisms are unidentified. Here, we demonstrate that the transcription factor BASIC LEUCINE ZIPPER63 (bZIP63) regulates the circadian oscillator gene PSEUDO RESPONSE REGULATOR7 (PRR7) to change the circadian phase in response to sugars. We find that SnRK1, a sugar-sensing kinase that regulates bZIP63 activity and circadian period [10-14] is required for sucrose-induced changes in circadian phase. Furthermore, TREHALOSE-6-PHOSPHATE SYNTHASE1 (TPS1), which synthesizes the signaling sugar trehalose-6-phosphate, is required for circadian phase adjustment in response to sucrose. We demonstrate that daily rhythms of energy availability can entrain the circadian oscillator through the function of bZIP63, TPS1, and the KIN10 subunit of the SnRK1 energy sensor. This identifies a molecular mechanism that adjusts the circadian phase in response to sugars.

Common bean reaction to angular leaf spot comprises transcriptional modulation of genes in the ALS10.1 QTL.

Genetic resistance of common bean (Phaseolus vulgaris L.) against angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola, is conferred by quantitative trait loci (QTL). In this study, we determined the gene content of the major QTL ALS10.1 located at the end of chromosome Pv10, and identified those that are responsive to ALS infection in resistant (CAL 143) and susceptible (IAC-UNA) genotypes. Based on the current version of the common bean reference genome, the ALS10.1 core region contains 323 genes. Gene Ontology (GO) analysis of these coding sequences revealed the presence of genes involved in signal perception and transduction, programmed cell death (PCD), and defense responses. Two putative R gene clusters were found at ALS10.1 containing evolutionary related coding sequences. Among them, the Phvul.010G025700 was consistently up-regulated in the infected IAC-UNA suggesting its contribution to plant susceptibility to the fungus. We identified six other genes that were regulated during common bean response to P. griseola; three of them might be negative regulators of immunity as they showed opposite expression patterns during resistant and susceptible reactions at the initial phase of fungal infection. Taken together, these findings suggest that common bean reaction to P. griseola involves transcriptional modulation of defense genes in the ALS10.1 locus, contributing to resistance or susceptibility depending on the plant-pathogen interaction.