Antibacterial activity of plant methanolic extracts on a field isolate of <i>Pseudomonas syringae</i>pvtomato from the Casablanca region (Morocco)

A bacterial field isolate recovered from infected tomato plants in a green-house at Sidi Rehal, a region near Casablanca city (Morocco), was identified as the gammaproteobacterium Pseudomonas syringae pv. tomato DC3000 strain, the causal agent of bacterial speck. The bacterial isolate was characterized by morphological, biochemical and molecular biological tests, its growth curves carried out in various culture media, and its phytopathogenicity verified by infection tests. A screening was performed to evaluate the antibacterial activity of methanolic extracts of 12 selected Moroccan plants against the P. syringae pv. tomato DC3000 isolate, and Agar-well diffusion and Broth microdilution methods were used to determine minimum inhibitory and minimum bactericidal concentrations. Among the methanolic extracts tested, only those of Nigella sativa, Geranuim robertianum, Aizoon canariense and Rubia peregrine showed clear inhibitory and bactericidal activities, although the highest values were achieved with N. sativa, a plant used in Morocco as a spice, condiment and medicinal treatment.

Identification of an extracellular infection-induced glyceraldehyde-3-phosphate dehydrogenase of the phytopathogenic proteobacterium <i>Pseudomonas syringae</i>pv tomato DC3000

According to molecular biology, genomic and proteomic data, the phytopathogenic gamma-proteobacterium Pseudomonas syringae pv. tomato DC3000 produces a number of proteins that may promote infection and draw nutrients from plants. Remarkably, P. syringae DC3000 strain possesses three paralogous gap genes encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH) enzymes with different predicted molecular sizes and metabolic functions. As GAPDH was shown to be a virulence factor in other microbial pathogens, in the current study, we analyzed the expression levels of each paralogous gap gene by realtime PCR to understand the actual impact of their protein products on P. syringae virulence. We found that all of them were strongly induced during the infection process. Nevertheless, proteomic analysis of culture supernatants revealed that only Class I GAPDH1 encoded by the gap1 gene was identified as an extracellular protein in infective cells. These results strongly suggest that this GAPDH should play a role in the infective process, including its well-know enzymatic function in the glycolytic metabolic pathway.

Plant peroxisomal solute transporter proteins

Plant peroxisomes are unique subcellular organelles which play an indispensable role in several key metabolic pathways, including fatty acid b-oxidation,photorespiration, and degradation of reactive oxygen species. The compartmentalization of metabolic pathways into peroxisomes is a strategy for organizing the metabolic network and improving pathway efficiency. An important prerequisite, however, is the exchange of metabolites between peroxisomes and other cell compartments. Since the first studies in the 1970s scientists contributed to understanding how solutes enter or leave this organelle.This review gives an overview about our current knowledge of the solute permeability of peroxisomal membranes described in plants, yeast, mammals and other eukaryotes. In general, peroxisomes contain in their bilayer membrane specific transporters for hydrophobic fatty acids(ABC transporter) and large cofactor molecules(carrier for ATP, NAD and CoA). Smaller solutes with molecular masses below 300–400 Da, like the organic acids malate, oxaloacetate, and 2-oxoglutarate, are shuttled via non-selective channels across the peroxisomal membrane.In comparison to yeast, human, mammals and other eukaryotes, the function of these known peroxisomal transporters and channels in plants are discussed in this review.

Plastid Signals and the Bundle Sheath： Mesophyll Development in Reticulate Mutants

The development of a plant leaf is a meticulously orchestrated sequence of events producing a complex organ comprising diverse cell types. The reticulate class of leaf variegation mutants displays contrasting pigmentation between veins and interveinal regions due to specific aberrations in the development of mesophyll cells. Thus, the reticulate mutants offer a potent tool to investigate cell-type-specific developmental processes. The discovery that most mutants are affected in plastid-localized, metabolic pathways that are strongly expressed in vasculature-associated tis- sues implicates a crucial role for the bundle sheath and their chloroplasts in proper development of the mesophyll cells. Here, we review the reticulate mutants and their phenotypic characteristics, with a focus on those in Arabidopsis thali- ana. Two alternative models have been put forward to explain the relationship between plastid metabolism and meso- phyll cell development, which we call here the supply and the signaling hypotheses. We critically assess these proposed models and discuss their implications for leaf development and bundle sheath function in C3 species. The characteriza- tion of the reticulate mutants supports the significance of plastid retrograde signaling in cell development and highlights the significance of the bundle sheath in C3 photosynthesis.

Regulation of floral senescence in Arabidopsis by coordinated action of CONSTANS and jasmonate signaling

In Arabidopsis,photoperiodic flowering is controlled by the regulatory hub gene CONSTANS(CO),whereas floral organ senescence is regulated by the jasmonates(JAs).Because these processes are chronologically ordered,it remains unknown whether there are common regulators of both processes.In this study,we discovered that CO protein accumulates in Arabidopsis flowers after floral induction,and it displays a diurnal pattern in floral organs different from that in the leaves.We observed that altered CO expression could affect flower senescence and abscission by interfering with JA response,as shown by petal-specific transcriptomic analysis as well as CO overexpression in JA synthesis and signaling mutants.We found that CO has a ZIM(ZINC-FINGER INFLORESCENCE MERISTEM)like domain that mediates its interaction with the JA response repressor JAZ3(jasmonate ZIM-domain 3).Their interaction inhibits the repressor activity of JAZ3,resulting in activation of downstream transcription factors involved in promoting flower senescence.Furthermore,we showed that CO,JAZ3,and the E3 ubiquitin ligase COI1(Coronatine Insensitive 1)could form a protein complex in planta,which promotes the degradation of both CO and JAZ3 in the presence of JAs.Taken together,our results indicate that CO,a key regulator of photoperiodic flowering,is also involved in promoting flower senescence and abscission by augmenting JA signaling and response.We propose that coordinated recruitment of photoperiodic and JA signaling pathways could be an efficient way for plants to chronologically order floral processes and ensure the success of offspring production.

Surveying the Oligomeric State of Arabidopsis thaliana Chloroplasts

Blue native-PAGE （BN-PAGE） resolves protein complexes in their native state. When combined with immu- noblotting, it can be used to identify the presence of high molecular weight complexes at high resolution for any protein, given a suitable antibody. To identify proteins in high molecular weight complexes on a large scale and to bypass the requirement for specific antibodies, we applied a tandem mass spectrometry （MS/MS） approach to BN-PAGE-resolved chloroplasts. Fractionation of the gel into six bands allowed iden- tification and label-free quantification of 1000 chloroplast proteins with native molecular weight separation. Significantly, this approach achieves a depth of identification comparable with traditional shotgun proteo- mic analyses of chloroplasts, indicating much of the known chloroplast proteome is amenable to MS/MS identification under our fractionation scheme. By limiting the number of fractionation bands to six, we facil- itate scaled-up comparative analyses, as we demonstrate with the reticulata chloroplast mutant displaying a reticulated leaf phenotype. Our comparative proteomics approach identified a candidate interacting protein of RETICULATA as well as effects on lipid remodeling proteins, amino acid metabolic enzymes, and plastid division machinery. We additionally highlight selected proteins from each sub-compartment of the chloroplast that provide novel insight on known or hypothesized protein complexes to further illus- trate the utility of this approach. Our results demonstrate the high sensitivity and reproducibility of this technique, which is anticipated to be widely adaptable to other sub-cellular compartments.

The Leaf Reticulate Mutant dovl Is Impaired in the First Step of Purine Metabolism

A series of reticulated Arabidopsis thaliana mutants were previously described. All mutants show a reticulate leaf pattern, namely green veins on a pale leaf lamina. They have an aberrant mesophyll structure but an intact layer of bundle sheath cells around the veins. Here, we unravel the function of the previously described reticulated EMS-mutant dovl （differential development of vascular associated cells 1）. By positional cloning, we identified the mutated gene, which encodes glutamine phosphoribosyl pyrophosphate aminotransferase 2 （ATase2）, an enzyme catalyzing the first step of purine nucleotide biosynthesis, dovl is allelic to the previously characterized cial-2 mutant that was isolated in a screen for mutants with impaired chloroplast protein import. We show that purine-derived total cytokinins are lowered in clovl and crosses with phytohormone reporter lines revealed differential reporter activity patterns in dovl. Metabolite profiling unraveled that amino acids that are involved in purine biosynthesis are increased in dovl. This study identified the mo- lecular basis of an established mutant line, which has the potential for further investigation of the interaction between metabolism and leaf development.

Improving photosynthetic efficiency toward food security:Strategies,advances,and perspectives

Photosynthesis in crops and natural vegetation allows light energy to be converted into chemical energy and thus forms the foundation for almost all terrestrial trophic networks on Earth.The efficiency of photosynthetic energy conversion plays a crucial role in determining the portion of incident solar radiation that can be used to generate plant biomass throughout a growth season.Consequently,alongside the factors such as resource availability,crop management,crop selection,maintenance costs,and intrinsic yield potential,photosynthetic energy use efficiency significantly influences crop yield.Photosynthetic efficiency is relevant to sustainability and food security because it affects water use efficiency,nutrient use efficiency,and land use efficiency.This review focuses specifically on the potential for improvements in photosynthetic efficiency to drive a sustainable increase in crop yields.We discuss bypassing photorespiration,enhancing light use efficiency,harnessing natural variation in photosynthetic parameters for breeding purposes,and adopting new-to-nature approaches that show promise for achieving unprecedented gains in photosynthetic efficiency.

Arabidopsis tic62 trol Mutant Lacking Thylakoid- Bound Ferredoxin-NADP＋ Oxidoreductase Shows Distinct Metabolic Phenotype

Ferredoxin-NADP＋ oxidoreductase （FNR）, functioning in the last step of the photosynthetic electron transfer chain, exists both as a soluble protein in the chloroplast stroma and tightly attached to chloroplast membranes. Surface plasmon resonance assays showed that the two FNR isoforms, LFNR1 and LFNR2, are bound to the thylakoid membrane via the C-terminal domains of Tic62 and TROL proteins in a pH-dependent manner. The tic62 trol double mutants contained a reduced level of FNR, exclusively found in the soluble stroma. Although the mutant plants showed no visual phenotype or defects in the function of photosystems under any conditions studied, a low ratio of NADPH/NADP~ was detected. Since the CO2 fixation capacity did not differ between the tic62 trol plants and wild-type, it seems that the plants are able to funnel reducing power to most crucial reactions to ensure survival and fitness of the plants. However, the activity of malate dehydrogenase was down-regulated in the mutant plants. Apparently, the plastid metabolism is able to cope with substantial changes in directing the electrons from the light reactions to stromal metabolism and thus only few differences are visible in steady-state metabolite pool sizes of the tic62 trol plants.