No abstract

Pollen thermotolerance. Global warming is predicted to increase the frequency and severity of extreme weather phenomena such as heat waves thereby posing a major threat for crop productivity and food security. The yield in case of most crop species is dependent on the success of reproductive development. Pollen development has been shown to be highly sensitive to elevated temperatures while the development of the female gametophyte as well as sporophytic tissues might also be disturbed under mild or severe heat stress conditions. Therefore, assessing pollen thermotolerance is currently of high interest for geneticists, plant biologists and breeders. A key aspect in pollen thermotolerance studies is the selection of the appropriate heat stress regime, the developmental stage that the stress is applied to, as well as the method of application. Literature search reveals a rather high variability in heat stress treatments mainly due to the lack of standardized protocols for different plant species. In this review, we summarize and discuss experimental approaches that have been used in various crops, with special focus on tomato, rice and wheat, as the best studied crops regarding pollen thermotolerance. The overview of stress treatments and the major outcomes of each study aim to provide guidelines for similar research in other crops.

Oxylipin metabolism represents one of many defence mechanisms employed by plants. It begins with the oxygenation of polyunsaturated fatty acids by lipoxygenases to form fatty acid hydroperoxides that are substrates for several enzymes, including specialized cytochrome P450s known as CYP74s. The targeting of a new CYP74, a 9-hydroperoxide lyase (HPL) from almonds, to the endomembrane system and lipid bodies, both as enzyme activity in almond seeds and as GFP fusions transiently expressed in tobacco protoplasts, is described. Such association of a CYP74 with lipid bodies has not been reported previously. Also described are the properties of a 9-HPL gene, the developmental regulation of its expression, the production and characterization of recombinant 9-HPL in Escherichia coli, and the developmental correlation between gene expression, enzyme activity, and the appearance of volatile C9 aldehydes from HPL action.

A subset of homeodomain leucine zipper proteins (HDZip) play a role in regulating adaptation responses including developmental adjustment to environmental cues in plants. Here we report the structural and functional characterisation of a dehydration responsive nuclear-targeted HDZip transcriptional regulator, CpHB-7. DNA-protein interaction studies suggest that CDeT6-19, a known ABA and dehydration responsive dehydrin gene, is a potential target gene of CpHB-7 in the desiccation-tolerant plant Craterostigma plantagineum. Transgenic plants that ectopically express CpHB-7 display reduced sensitivity towards ABA during seed germination and stomatal closure. Expression analysis reveals that genes with induced or repressed expression in CpHB-7 ectopic expression lines are either mostly repressed or induced by ABA, drought or salt treatment respectively, thus demonstrating that CpHB-7 modifies ABA-responsive gene expression as a negative regulator. CpHB-7 gene expression is also linked to early organ development, leading to the suggestion that CpHB-7 is functionally similar to the Arabidopsis transcription factor, ATHB-6.

BackgroundThe unprecedented role of sncRNAs in the regulation of pollen biogenesis on both transcriptional and epigenetic levels has been experimentally proven. However, little is known about their global regulation, especially under stress conditions. We used tomato pollen in order to identify pollen stage-specific sncRNAs and their target mRNAs. We further deployed elevated temperatures to discern stress responsive sncRNAs. For this purpose high throughput sncRNA-sequencing as well as Massive Analysis of cDNA Ends (MACE) were performed for three-replicated sncRNAs libraries derived from tomato tetrad, post-meiotic, and mature pollen under control and heat stress conditions.ResultsUsing the omiRas analysis pipeline we identified known and predicted novel miRNAs as well as sncRNAs from other classes, responsive or not to heat. Differential expression analysis revealed that post-meiotic and mature pollen react most strongly by regulation of the expression of coding and non-coding genomic regions in response to heat. To gain insight to the function of these miRNAs, we predicted targets and annotated them to Gene Ontology terms. This approach revealed that most of them belong to protein binding, transcription, and Serine/Threonine kinase activity GO categories. Beside miRNAs, we observed differential expression of both tRNAs and snoRNAs in tetrad, post-meiotic, and mature pollen when comparing normal and heat stress conditions.ConclusionsThus, we describe a global spectrum of sncRNAs expressed in pollen as well as unveiled those which are regulated at specific time-points during pollen biogenesis. We integrated the small RNAs into the regulatory network of tomato heat stress response in pollen.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1901-x) contains supplementary material, which is available to authorized users.

Phyto-oxylipins are a group of biologically active molecules that play an important role in plant defence. Their production begins with the oxygenation of polyunsaturated fatty acids by lipoxygenases (LOX) to form 9- or 13-hydroperoxides that are substrates for several enzymes involved in the synthesis of final oxylipins, which can act as signal molecules and/or direct antimicrobials. In the present work, the response of the 9-LOX pathway in the almond/Aspergillus carbonarius (producer of ochratoxin A) interaction was studied. Both LOX gene expression and activity are up-regulated over the course of fungal infection in immature and mature almonds. The biochemical characterization of major LOX and hydroperoxide lyase (HPL) isoforms indicated that 9-LOX metabolism is specifically induced by A. carbonarius. Lipid peroxidation profiling showed that, in infected immature almonds, enzymatically produced 9-hydro(peroxy) fatty acids (HFAs) were the main HFAs and are further metabolized by HPL into C9-aldehydes. Both HPL gene expression and C9-aldehydes increased over the course of fungal infection. In mature almonds infected with A. carbonarius, levels of LOX expression and activity were lower than those found in immature seeds, and 9-HFA represented the minority of total HFA, which consisted of mostly 13- and non-enzymatically produced HFA. In these experimental conditions, no volatile aldehydes were recorded from these samples, even though HPL was up-regulated in infected mature almonds. The effects on the growth of A. carbonarius of the aldehydes produced by these enzymes were also tested in vitro. Results reported here led to the proposal that, in almond seed, the association of 9-LOX and HPL has an important role in seed defence mechanism against pathogen infection.

Recently, we purified to homogeneity and characterized a low-molecular-weight calcium-dependent phospholipase A2 (PLA2) from developing elm seed endosperm. This represented the first purified and characterized PLA2 from a plant tissue. The full sequences of two distinct but homologous rice (Oryza sativa) cDNAs are given here. These encode mature proteins of 1 19 amino acids (PLA2-I, preceded by a 19 amino acid signal peptide) and 128 amino acids (PLA2-II. preceded by a 25 amino acid signal peptide), and were derived from four expressed sequence tag (EST) clones. Both proteins were homologous to the N-terminal amino acid sequence of the elm PLA2. They contained twelve conserved cysteine residues and sequences that are likely to represent the Ca(2+)-binding loop and active-site motif, which are characteristic of animal secretory PLA2s. A soluble PLA2s activity was purified 145 000-fold from green rice shoots. This had the same biochemical characteristics as the elm and animal secretory PLA2s. The purified rice PLA2 consisted of two proteins, with a molecular weight of 12 440 and 12 920, that had identical N-terminal amino acid sequences. This sequence was different from but homologous to the PLA2-I and PLA2-II sequences. Taken together, the results suggest that at least three different low-molecular-weight PLA2s are expressed in green rice shoots. Southern blot analysis suggested that multiple copies of such genes are likely to occur in the rice and in other plant genomes.

Heat shock proteins (HSPs), highly conserved in all organisms, act as molecular chaperones activated by several stresses. The HSP70 class of stress-induced proteins is the most studied subtype in cardiovascular and inflammatory disease. Because of the high similarity between plant and mammalian HSP70, the aim of this work was to evaluate whether recombinant HSP70 of plant origin (r-AtHSP70) was able to protect rat cardiac and hepatic function under ischemic and sepsis conditions. We demonstrated for the first time that, in ex vivo isolated and perfused rat heart, exogenous r-AtHSP70 exerted direct negative inotropic and lusitropic effects via Akt/endothelial nitric oxide synthase pathway, induced post-conditioning cardioprotection via Reperfusion Injury Salvage Kinase and Survivor Activating Factor Enhancement pathways, and did not cause hepatic damage. In vivo administration of r-AtHSP70 protected both heart and liver against lipopolysaccharide-dependent sepsis, as revealed by the reduced plasma levels of interleukin-1β, tumour necrosis factor alpha, aspartate aminotransferase and alanine aminotransferase. These results suggest exogenous r-AtHSP70 as a molecular modulator able to protect myocardial function and to prevent cardiac and liver dysfunctions during inflammatory conditions.