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SUMMARY: Plants acquire phosphorus (P) primarily as inorganic phosphate (Pi) from the soil. Under Pi deficiency, plants induce an array of physiological and morphological responses, termed phosphate starvation response (PSR), thereby increasing Pi acquisition and use efficiency. However, the mechanisms by which plants adapt to Pi deficiency remain to be elucidated. Here, we report that deposition of a β‐1,3‐glucan polymer called callose is induced in Arabidopsis thaliana root hairs under Pi deficiency, in a manner independent of PSR‐regulating PHR1/PHL1 transcription factors and LPR1/LPR2 ferroxidases. Genetic studies revealed PMR4 (GSL5) callose synthase being required for the callose deposition in Pi‐depleted root hairs. Loss of PMR4 also reduces Pi acquisition in shoots and plant growth under low Pi conditions. The defects are not recovered by simultaneous disruption of SID2, mediating defense‐associated salicylic acid (SA) biosynthesis, excluding SA defense activation from the cause of the observed pmr4 phenotypes. Grafting experiments and characterization of plants expressing PMR4 specifically in root hair cells suggest that a PMR4 pool in the cell type contributes to shoot growth under Pi deficiency. Our findings thus suggest an important role for PMR4 in plant adaptation to Pi deficiency. [ABSTRACT FROM AUTHOR]

Summary: Plant defense against herbivores is modulated by herbivore‐associated molecular patterns (HAMPs) from oral secretions (OS) and/or saliva of insects. Furthermore, feeding wounds initiate plant self‐damage responses modulated by danger‐associated molecular patterns (DAMPs) such as immune defense‐promoting plant elicitor peptides (Peps). While temporal and spatial co‐existence of both patterns during herbivory implies a possibility of their close interaction, the molecular mechanisms remain undetermined. Here we report that exogenous application of rice (Oryza sativa) peptides (OsPeps) can elicit multiple defense responses in rice cell cultures. Specific activation of OsPROPEP3 gene transcripts in rice leaves by wounding and OS treatments further suggests a possible involvement of the OsPep3 peptide in rice–herbivore interactions. Correspondingly, we found that simultaneous application of OsPep3 and Mythimna loreyi OS significantly amplifies an array of defense responses in rice cells, including mitogen‐activated protein kinase activation, and generation of defense‐related hormones and metabolites. The induction of OsPROPEP3/4 by OsPep3 points to a positive auto‐feedback loop in OsPep signaling which may contribute to additional enhancement of defense signal(s). Finally, the overexpression of the OsPep receptor OsPEPR1 increases the sensitivity of rice plants not only to the cognate OsPeps but also to OS signals. Our findings collectively suggest that HAMP–DAMP signal integration provides a critical step in the amplification of defense signaling in plants. [ABSTRACT FROM AUTHOR]

Summary: In mammalian cells, the transcription factor p53 plays a crucial role in transmitting DNA damage signals to maintain genome integrity. However, in plants, orthologous genes for p53 and checkpoint proteins are absent. Instead, the plant‐specific transcription factor SUPPRESSOR OF GAMMA RESPONSE 1 (SOG1) controls most of the genes induced by gamma irradiation and promotes DNA repair, cell cycle arrest, and stem cell death. To date, the genes directly controlled by SOG1 remain largely unknown, limiting the understanding of DNA damage signaling in plants. Here, we conducted a microarray analysis and chromatin immunoprecipitation (ChIP)‐sequencing, and identified 146 Arabidopsis genes as direct targets of SOG1. By using ChIP‐sequencing data, we extracted the palindromic motif [CTT(N)7AAG] as a consensus SOG1‐binding sequence, which mediates target gene induction in response to DNA damage. Furthermore, DNA damage‐triggered phosphorylation of SOG1 is required for efficient binding to the SOG1‐binding sequence. Comparison between SOG1 and p53 target genes showed that both transcription factors control genes responsible for cell cycle regulation, such as CDK inhibitors, and DNA repair, whereas SOG1 preferentially targets genes involved in homologous recombination. We also found that defense‐related genes were enriched in the SOG1 target genes. Consistent with this finding, SOG1 is required for resistance against the hemi‐biotrophic fungus Colletotrichum higginsianum, suggesting that SOG1 has a unique function in controlling the immune response. [ABSTRACT FROM AUTHOR]

Summary: Plants solely rely on innate immunity of each individual cell to deal with a diversity of microbes in the environment. Extracellular recognition of microbe‐ and host damage‐associated molecular patterns leads to the first layer of inducible defenses, termed pattern‐triggered immunity (PTI). In plants, pattern recognition receptors (PRRs) described to date are all membrane‐associated receptor‐like kinases or receptor‐like proteins, reflecting the prevalence of apoplastic colonization of plant‐infecting microbes. An increasing inventory of elicitor‐active patterns and PRRs indicates that a large number of them are limited to a certain range of plant groups/species, pointing to dynamic and convergent evolution of pattern recognition specificities. In addition to common molecular principles of PRR signaling, recent studies have revealed substantial diversification between PRRs in their functions and regulatory mechanisms. This serves to confer robustness and plasticity to the whole PTI system in natural infections, wherein different PRRs are simultaneously engaged and faced with microbial assaults. We review the functional significance and molecular basis of PRR‐mediated pathogen recognition and disease resistance, and also an emerging role for PRRs in homeostatic association with beneficial or commensal microbes. [ABSTRACT FROM AUTHOR]

Tandem affinity purification (TAP) strategies constitute an efficient approach for protein complex purification from many different organisms. However, the application of such strategies for purifying endogenous Arabidopsis multi-protein complexes has not yet been reported. Here, we describe an alternative TAP (TAPa) system that successfully allows protein complex purification from Arabidopsis. In our newly generated TAPa tag we have replaced the tobacco etch virus (TEV) protease cleavage site with the more specific and low-temperature active rhinovirus 3C protease site. In addition, the second purification step can now be performed through two different affinity tags: a six His repeat or nine copies of a myc repeat. To examine our purification procedure we generated a C-terminal fusion between the TAPa tag and CSN3, a component of the multi-protein COP9 signalosome (CSN) complex. Subsequent analysis showed that CSN3-TAPa could rescue acsn3mutant, and that the components of the CSN complex could be co-purified with CSN3-TAPa. As part of our long running interest in light signaling in Arabidopsis we have generated Arabidopsis transgenic lines harboring, both N-terminal and C-terminal TAPa fusions of many different light signaling pathway regulators. Molecular characterization of these transgenic lines showed fusion expression in 88% of the genes analyzed and that this expression is largely independent of the fusion orientation. Mutant complementation analysis showed that most of the TAPa fusions analyzed retained function of the wild-type proteins. Taken together, the data demonstrate the suitability of the TAPa system to allow efficient multi-protein complex isolation from stably transformed Arabidopsis. [ABSTRACT FROM AUTHOR]

Summary A rice gene encoding a calcium-dependent protein kinase (CDPK), OsCDPK7, was induced by cold and salt stresses. To elucidate the physiological function of OsCDPK7, we generated transgenic rice plants with altered levels of the protein. The extent of tolerance to cold and salt/drought stresses of these plants correlated well with the level of OsCDPK7 expression. Therefore, OsCDPK7 was shown to be a positive regulator commonly involved in the tolerance to both stresses in rice. Over-expression of OsCDPK7 enhanced induction of some stress-responsive genes in response to salinity/drought, but not to cold. Thus, it was suggested that the downstream pathways leading to the cold and salt/drought tolerance are different from each other. It seems likely that at least two distinct pathways commonly use a single CDPK, maintaining the signalling specificity through unknown post-translational regulation mechanisms. These results demonstrate that simple manipulation of CDPK activity has great potential with regard to plant improvement. [ABSTRACT FROM AUTHOR]