Salinity-Induced Variation in Biochemical Markers Provides Insight into the Mechanisms of Salt Tolerance in Common (Phaseolus vulgaris) and Runner (P. coccineus) Beans

The evaluation of biochemical markers is important for the understanding of the mechanisms of tolerance to salinity of Phaseolus beans. We have evaluated several growth parameters in young plants of three Phaseolus vulgaris cultivars subjected to four salinity levels (0, 50, 100, and 150 mM NaCl); one cultivar of P. coccineus, a closely related species reported as more salt tolerant than common bean, was included as external reference. Biochemical parameters evaluated in leaves of young plants included the concentrations of ions (Na⁺, K⁺, and Cl⁻), osmolytes (proline, glycine betaine, and total soluble sugars), and individual soluble carbohydrates. Considerable differences were found among cultivars, salinity levels, and in their interaction for most traits. In general, the linear component of the salinity factor for the growth parameters and biochemical markers was the most important. Large differences in the salinity response were found, with P. vulgaris cultivars “The Prince” and “Maxidor” being, respectively, the most susceptible and tolerant ones. Our results support that salt stress tolerance in beans is mostly based on restriction of Na⁺ (and, to a lesser extent, also of Cl⁻) transport to shoots, and on the accumulation of myo-inositol for osmotic adjustment. These responses to stress during vegetative growth appear to be more efficient in the tolerant P. vulgaris cultivar “Maxidor”. Proline accumulation is a reliable marker of the level of salt stress affecting Phaseolus plants, but does not seem to be directly related to stress tolerance mechanisms. These results provide useful information on the responses to salinity of Phaseolus.     

Identification and Expression Analysis of Candidate Genes Associated with Defense Responses to Phytophthora capsici in Pepper Line “PI 201234”

Phytophthora capsici (Leonian), classified as an oomycete, seriously threatens the production of pepper (Capsicum annuum). Current understanding of the defense responses in pepper to P. capsici is limited. In this study, RNA-sequencing analysis was utilized to identify differentially expressed genes in the resistant line “PI 201234”, with 1220 differentially expressed genes detected. Of those genes, 480 were up-regulated and 740 were down-regulated, with 211 candidate genes found to be involved in defense responses based on the gene annotations. Furthermore, the expression patterns of 12 candidate genes were further validated via quantitative real-time PCR (qPCR). These genes were found to be significantly up-regulated at different time points post-inoculation (6 hpi, 24 hpi, and 5 dpi) in the resistant line “PI 201234” and susceptible line “Qiemen”. Seven genes were found to be involved in cell wall modification, phytoalexin biosynthesis, symptom development, and phytohormone signaling pathways, thus possibly playing important roles in combating exogenous pathogens. The genes identified herein will provide a basis for further gene cloning and functional verification studies and will aid in an understanding of the regulatory mechanism of pepper resistance to P. capsici.     

Response of Different Genotypes of Faba Bean Plant to Drought Stress

Drought stress is one of the major abiotic stresses that are a threat to crop production worldwide. Drought stress impairs the plants growth and yield. Therefore, the aim of the present experiment was to select the tolerant genotype/s on the basis of moprpho-physiological and biochemical characteristics of 10 Vicia faba genotypes (Zafar 1, Zafar 2, Shebam, Makamora, Espan, Giza Blanka, Giza 3, C4, C5 and G853) under drought stress. We studied the effect of different levels of drought stress i.e., (i) normal irrigation (ii) mild stress (iii) moderate stress, and (iv) severe stress on plant height (PH) plant⁻¹, fresh weight (FW) and dry weight (DW) plant⁻¹, area leaf⁻¹, leaf relative water content (RWC), proline (Pro) content, total chlorophyll (Total Chl) content, electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content, and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) of genotypes of faba bean. Drought stress reduced all growth parameters and Total Chl content of all genotypes. However, the deteriorating effect of drought stress on the growth performance of genotypes “C5” and “Zafar 1” were relatively low due to its better antioxidant enzymes activities (CAT, POD and SOD), and accumulation of Pro and Total Chl, and leaf RWC. In the study, genotype “C5” and “Zafar 1” were found to be relatively tolerant to drought stress and genotypes “G853” and “C4” were sensitive to drought stress.     

Genotypic Variation under Fe Deficiency Results in Rapid Changes in Protein Expressions and Genes Involved in Fe Metabolism and Antioxidant Mechanisms in Tomato Seedlings (Solanum lycopersicum L.)

To investigate Fe deficiency tolerance in tomato cultivars, quantification of proteins and genes involved in Fe metabolism and antioxidant mechanisms were performed in “Roggusanmaru” and “Super Doterang”. Fe deficiency (Moderate, low and –Fe) significantly decreased the biomass, total, and apoplastic Fe concentration of “Roggusanmaru”, while a slight variation was observed in “Super Doterang” cultivar. The quantity of important photosynthetic pigments such as total chlorophyll and carotenoid contents significantly decreased in “Roggusanmaru” than “Super Doterang” cultivar. The total protein profile in leaves and roots determines that “Super Doterang” exhibited an optimal tolerance to Fe deficiency compared to “Roggusanmaru” cultivar. A reduction in expression of PSI (photosystem I), PSII (photosystem II) super-complexes and related thylakoid protein contents were detected in “Roggusanmaru” than “Super Doterang” cultivar. Moreover, the relative gene expression of SlPSI and SlPSII were well maintained in “Super Doterang” than “Roggusanmaru” cultivar. The relative expression of genes involved in Fe-transport (SlIRT1 and SlIRT2) and Fe(III) chelates reductase oxidase (SlFRO1) were relatively reduced in “Roggusanmaru”, while increased in “Super Doterang” cultivar under Fe deficient conditions. The H⁺-ATPase relative gene expression (SlAHA1) in roots were maintained in “Super Doterang” compared to “Roggusanmaru”. Furthermore, the gene expressions involved in antioxidant defense mechanisms (SlSOD, SlAPX and SlCAT) in leaves and roots showed that these genes were highly increased in “Super Doterang”, whereas decreased in “Roggusanmaru” cultivar under Fe deficiency. The present study suggested that “Super Doterang” is better tomato cultivar than “Roggusanmaru” for calcareous soils.     

Sugarcane Serine Peptidase Inhibitors,Serine Peptidases,and Clp Protease System Subunits Associated with Sugarcane Borer (Diatraea saccharalis) Herbivory and Wounding

Sugarcane’s (Saccharum spp.) response to Diatraea saccharalis (F.) (Lepidoptera: (Crambidae) herbivory was investigated using a macroarray spotted with 248 sugarcane Expressed Sequence Tags (ESTs) encoding serine peptidase inhibitors, serine peptidases. and Clp protease system subunits. Our results showed that after nine hours of herbivory, 13 sugarcane genes were upregulated and nine were downregulated. Among the upregulated genes, nine were similar to serine peptidase inhibitors and four were similar to Bowman-Birk Inhibitors (BBIs). Phylogenetic analysis revealed that these sequences belong to a phylogenetic group of sugarcane BBIs that are potentially involved in plant defense against insect predation. The remaining four upregulated genes included serine peptidases and one homolog to the Arabidopsis AAA+ chaperone subunit ClpD, which is a member of the Clp protease system. Among the downregulated genes, five were homologous to serine peptidases and four were homologous to Arabidopsis Clp subunits (three homologous to Clp AAA+ chaperones and one to a ClpP-related ClpR subunit). Although the roles of serine peptidase inhibitors in plant defenses against herbivory have been extensively investigated, the roles of plant serine peptidases and the Clp protease system represent a new and underexplored field of study. The up- and downregulated D. saccharalis genes presented in this study may be candidate genes for the further investigation of the sugarcane response to herbivory.     

CrWSKP1, an SKP1-like Gene,Is Involved in the Self-Incompatibility Reaction of “Wuzishatangju” (Citrus reticulata Blanco)

Plant S-phase kinase-associated protein 1 (SKP1) genes play crucial roles in plant development and differentiation. However, the role of SKP1 in citrus is unclear. Herein, we described a novel SKP1-like gene, designated as CrWSKP1, from “Wuzishatangju” (Citrus reticulata Blanco). The cDNA sequence of CrWSKP1 is 779 base pairs (bp) and contains an open reading frame (ORF) of 477 bp. The genomic sequence of the CrWSKP1 gene is 1296 bp with two exons and one intron. CrWSKP1 has high identity with SKP1-like genes from other plant species within two conserved regions. Approximately 85% of pollen tubes of self-pollinated CrWSKP1 transgenic tobaccos became twisted at four days after self-pollination. Pollen tube numbers of self-pollinated CrWSKP1 transformants entering into ovules were significantly fewer than that of the control. Seed number of self-pollinated CrWSKP1 transformants was significantly reduced. These results suggested that the CrWSKP1 is involved in the self-incompatibility (SI) reaction of “Wuzishatangju”.     

Characterization of Erysiphe necator-Responsive Genes in Chinese Wild Vitis quinquangularis

Powdery mildew (PM), caused by fungus Erysiphe necator, is one of the most devastating diseases of grapevine. To better understand grapevine-PM interaction and provide candidate resources for grapevine breeding, a suppression subtractive hybridization (SSH) cDNA library was constructed from E. necator-infected leaves of a resistant Chinese wild Vitis quinquangularis clone “Shang-24”. A total of 492 high quality expressed sequence tags (ESTs) were obtained and assembled into 266 unigenes. Gene ontology (GO) analysis indicated that 188 unigenes could be assigned with at least one GO term in the biological process category, and 176 in the molecular function category. Sequence analysis showed that a large number of these genes were homologous to those involved in defense responses. Genes involved in metabolism, photosynthesis, transport and signal transduction were also enriched in the library. Expression analysis of 13 selected genes by qRT-PCR revealed that most were induced more quickly and intensely in the resistant material “Shang-24” than in the sensitive V. pseudoreticulata clone “Hunan-1” by E. necator infection. The ESTs reported here provide new clues to understand the disease-resistance mechanism in Chinese wild grapevine species and may enable us to investigate E. necator-responsive genes involved in PM resistance in grapevine germplasm.     

Global Metabolic Regulation of the Snow Alga Chlamydomonas nivalis in Response to Nitrate or Phosphate Deprivation by a Metabolome Profile Analysis

In the present work, Chlamydomonas nivalis, a model species of snow algae, was used to illustrate the metabolic regulation mechanism of microalgae under nutrient deprivation stress. The seed culture was inoculated into the medium without nitrate or phosphate to reveal the cell responses by a metabolome profile analysis using gas chromatography time-of-flight mass spectrometry (GC/TOF-MS). One hundred and seventy-one of the identified metabolites clustered into five groups by the orthogonal partial least squares discriminant analysis (OPLS-DA) model. Among them, thirty of the metabolites in the nitrate-deprived group and thirty-nine of the metabolites in the phosphate-deprived group were selected and identified as “responding biomarkers” by this metabolomic approach. A significant change in the abundance of biomarkers indicated that the enhanced biosynthesis of carbohydrates and fatty acids coupled with the decreased biosynthesis of amino acids, N-compounds and organic acids in all the stress groups. The up- or down-regulation of these biomarkers in the metabolic network provides new insights into the global metabolic regulation and internal relationships within amino acid and fatty acid synthesis, glycolysis, the tricarboxylic acid cycle (TCA) and the Calvin cycle in the snow alga under nitrate or phosphate deprivation stress.