Plants have evolved a plethora of mechanisms to circumvent the potential damaging effects of living under low phosphorus availability in the soil. These mechanisms include different levels of organization, from root-shoot signalling at the whole-plant level to specific biochemical responses at the subcellular level, such as reductions in photosynthesis and the consequent activation of photo- and antioxidant mechanisms in chloroplasts. Some recent studies clearly indicate that severe phosphorus deficiency can lead to alterations in the photosynthetic apparatus, including reductions in CO2 assimilation rates, a down-regulation of photosynthesis-related genes and photoinhibition at the photosystem II level, thus causing potential photo-oxidative stress. Photo-oxidative stress is characterized by an increased production of reactive oxygen species in chloroplasts, which at low concentrations can serve a signalling, protective role, but when present at high concentrations can cause damage to lipids, proteins and nucleic acids, thus leading to irreversible injuries. We discuss here the mechanisms that phosphate-starved plants have evolved to withstand photo-oxidative stress, including changes at the subcellular level (e.g. activation of photo- and antioxidant protection mechanisms in chloroplasts), cellular and tissular levels (e.g. activation of photorespiration and anthocyanin accumulation) and whole-plant level (alterations in source-sink relationships modulated by hormones). Of particular importance is the current evidence demonstrating that phosphate-starved plants activate simultaneous responses at multiple levels, from transcriptional changes to root-shoot signalling, to prevent oxidative damage. In this review, we summarize current knowledge about the occurrence of photo-oxidative stress in phosphate-starved plants and highlight the mechanisms these plants have evolved to prevent oxidative damage under phosphorus limitation at the subcellular, cellular and whole-plant levels. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Cold stress adversely affects plant growth and development. Most temperate plants acquire freezing tolerance by a process called cold acclimation. Here, we focus on recent progress in transcriptional, post-transcriptional and post-translational regulation of gene expression that is critical for cold acclimation. Transcriptional regulation is mediated by the inducer of C-repeat binding factor (CBF) expression 1 (ICE1), the CBF transcriptional cascade and CBF-independent regulons during cold acclimation. ICE1 is negatively regulated by ubiquitination-mediated proteolysis and positively regulated by SUMO (small ubiquitin-related modifier) E3 ligase-catalyzed sumoylation. Post-transcriptional regulatory mechanisms, such as pre-mRNA splicing, mRNA export and small RNA-directed mRNA degradation, also play important roles in cold stress responses.

To understand the gene network controlling tolerance to cold stress, we performed an Arabidopsis thaliana genome transcript expression profile using Affymetrix GeneChips that contain ∼24,000 genes. We statistically determined 939 cold-regulated genes with 655 upregulated and 284 downregulated. A large number of early cold-responsive genes encode transcription factors that likely control late-responsive genes, suggesting a multitude of transcriptional cascades. In addition, many genes involved in chromatin level and posttranscriptional regulation were also cold regulated, suggesting their involvement in cold-responsive gene regulation. A number of genes important for the biosynthesis or signaling of plant hormones, such as abscisic acid, gibberellic acid, and auxin, are regulated by cold stress, which is of potential importance in coordinating cold tolerance with growth and development. We compared the cold-responsive transcriptomes of the wild type and inducer of CBF expression 1 (ice1), a mutant defective in an upstream transcription factor required for chilling and freezing tolerance. The transcript levels of many cold-responsive genes were altered in the ice1 mutant not only during cold stress but also before cold treatments. Our study provides a global picture of the Arabidopsis cold-responsive transcriptome and its control by ICE1 and will be valuable for understanding gene regulation under cold stress and the molecular mechanisms of cold tolerance.

The signaling events generated by a cold exposure are poorly known in plants. We were interested in checking the possible activation of enzymes of the phosphoinositide signaling pathway in response to a temperature drop. In Arabidopsis suspension cells labeled with (33)PO(4)(3-), a cold treatment induces a rapid increase of phosphatidic acid (PtdOH) content. This production was due to the simultaneous activation of phospholipase C (through diacylglycerol kinase activity) and phospholipase D, as monitored by the production of inositol triphosphate and of transphosphatidylation product, respectively. Moreover, inhibitors of the phosphoinositide pathway and of diacylglycerol kinase reduced PtdOH production. Enzyme activation occurred immediately after cells were transferred to low temperature. The respective contribution of both kind of phospholipases in cold-induced production of PtdOH could be estimated. We created conditions where phospholipids were labeled with (33)PO(4)(3-), but with ATP being nonradioactive. In such conditions, the apparition of radioactive PtdOH reflected PLD activity. Thus, we demonstrated that during a cold stress, phospholipase D activity accounted for 20% of PtdOH production. The analysis of composition in fatty acids of cold-produced PtdOH compared with that of different phospholipids confirmed that cold-induced PtdOH more likely derived mainly from phosphoinositides. The addition of chemical reagents modifying calcium availability inhibited the formation of PtdOH, showing that the cold-induced activation of phospholipase pathways is dependent on a calcium entry.

We have developed a DNA extraction procedure for milligram amounts of plant tissue. Yields ranged from 0.3-200 nanograms of DNA per milligram of tissue. The factors affecting yield are discussed. Fresh tissue, as well as herbarium specimens (22-118 years old) and mummified seeds and embryos (500 to greater than 44 600 years old) were used. All tissues attempted (57 types from 29 species) yielded measurable amounts of DNA. In no case tested was inhibition observed for restriction enzymes BamHI or EcoRI.

Reactive oxygen species (ROS) generated by NADPH oxidase (NOX) are crucial for tip growth of pollen tubes. However, the regulation of NOX activity in pollen tubes remains unknown. Using purified plasma membrane fractions from tobacco and olive pollen and tobacco BY-2 cells, we demonstrate that pollen NOX is activated by calcium ions and low abundant signaling phospholipids, such as phosphatidic acid and phosphatidylinositol 4,5-bisphosphate in vitro and in vivo. Our data also suggest possible synergism between Ca(2+) and phospholipid-mediated NOX activation in pollen. Rac/Rop small GTPases are also necessary for normal pollen tube growth and have been proposed to regulate ROS production in root hairs. We show here elevated ROS formation in pollen tubes overexpressing wild-type NtRac5 and constitutively active NtRac5, while overexpression of dominant-negative NtRac5 led to a decrease of ROS in pollen tubes. We also show that PA formed by distinct phospholipases D (PLD) is involved in pathways both upstream and downstream of NOX-mediated ROS generation and identify NtPLDδ as a PLD isoform acting in the ROS response pathway.Copyright © 2012 Elsevier GmbH. All rights reserved.

Both seed size and abiotic stress tolerance are important agronomic traits in crops. In Arabidopsis, two closely related transcription repressors DPA4 (Development-Related PcG Target in the APEX4)/NGAL3 and SOD7 (Suppressor of da1-1)/NGAL2 (NGATHA-like protein) function redundantly to regulate seed size, which was increased in the dpa4 sod7 double mutants. Whereas ABA-induced transcription repressors (AITRs) are involved in the regulation of ABA signaling and abiotic stress tolerance, Arabidopsis aitr2 aitr5 aitr6 (aitr256) triple mutant showed enhanced tolerance to drought and salt. Here we performed CRISPR/Cas9 genome editing to disrupt DPA4 and SOD7 in aitr256 mutant, trying to integrate seed size and abiotic stress tolerance traits in Arabidopsis, and also to examine whether DPA4 and SOD7 may regulate other aspects of plant growth and development. Indeed, seed size was increased in the dpa4 sod7 aitr256 quintuple mutants, and enhanced tolerance to drought was observed in the mutants. In addition, we found that shoot branching was affected in the dpa4 sod7 aitr256 mutants. The mutant plants failed to produce secondary branches, and flowers/siliques were distributed irregularly on the main stems of the plants. Floral organ number and fertility were also affected in the dpa4 sod7 aitr256 mutant plants. To examine if these phenotypes were dependent on loss-of-function of AITRs, dpa4 sod7 double mutants were generated in Col wild type background, and we found that the dpa4 sod7 mutant plants showed a phenotype similar to the dpa4 sod7 aitr256 quintuple mutants. Taken together, our results indicate that the integration of seed size and abiotic stress tolerance traits by CRISPR/Cas9 editing was successful, and our results also revealed a role of DPA4 and SOD7 in the regulation of inflorescence architecture in Arabidopsis.

The Arabidopsis thaliana dgat1 mutant, AS11, has an oil content which is decreased by 30%, and a strongly increased ratio of 18:3/20:1, compared to wild type. Despite lacking a functional DGAT1, AS11 still manages to make 70% of WT seed oil levels. Recently, it was demonstrated that in the absence of DGAT1, PDAT1 was essential for normal seed development, and is a dominant determinant in Arabidopsis TAG biosynthesis.

Lipid phosphorylation by diacylglycerol kinase (DGK) that produces phosphatidic acid (PA) plays important roles in various biological processes, including stress responses, but the underlying mechanisms remain elusive. Here, we show that DGK5 and its lipid product PA suppress ABA biosynthesis by interacting with ABA-DEFICIENT 2 (ABA2), a key ABA biosynthesis enzyme, to negatively modulate plant response to abiotic stress tested in Arabidopsis thaliana. Loss of DGK5 function rendered plants less damaged, whereas overexpression (OE) of DGK5 enhanced plant damage to water and salt stress. The dgk5 mutant plants exhibited decreased total cellular and nuclear levels of PA with increased levels of diacylglycerol, whereas DGK5-OE plants displayed the opposite effect. Interestingly, we found that both DGK5 and PA bind to the ABA-synthesizing enzyme ABA2 and suppress its enzymatic activity. Consistently, the dgk5 mutant plants exhibited increased levels of ABA, while DGK5-OE plants showed reduced ABA levels. In addition, we showed that both DGK5 and ABA2 are detected in and outside the nuclei, and loss of DGK5 function decreased the nuclear association of ABA2. We found that both DGK5 activity and PA promote nuclear association of ABA2. Taken together, these results indicate that both DGK5 and PA interact with ABA2 to inhibit its enzymatic activity and promote its nuclear sequestration, thereby suppressing ABA production in response to abiotic stress. Our study reveals a sophisticated mechanism by which DGK5 and PA regulate plant stress responses.Copyright © 2024 The Author. Published by Elsevier Inc. All rights reserved.