Heat stress (HS), caused by extremely high temperatures, is one of the most severe forms of abiotic stress in pepper. In the present study, we studied the transcriptome and metabolome of a heat-tolerant cultivar (17CL30) and a heat-sensitive cultivar (05S180) under HS. Briefly, we identified 5754 and 5756 differentially expressed genes (DEGs) in 17CL30 and 05S180, respectively. Moreover, we also identified 94 and 108 differentially accumulated metabolites (DAMs) in 17CL30 and 05S180, respectively. Interestingly, there were many common HS-responsive genes (approximately 30%) in both pepper cultivars, despite the expression patterns of these HS-responsive genes being different in both cultivars. Notably, the expression changes of the most common HS-responsive genes were typically much more significant in 17CL30, which might explain why 17CL30 was more heat tolerant. Similar results were also obtained from metabolome data, especially amino acids, organic acids, flavonoids, and sugars. The changes in numerous genes and metabolites emphasized the complex response mechanisms involved in HS in pepper. Collectively, our study suggested that the glutathione metabolic pathway played a critical role in pepper response to HS and the higher accumulation ability of related genes and metabolites might be one of the primary reasons contributing to the heat resistance.

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Background:Developing algal industries in saline-alkali areas is necessary. However, suitable strains and optimal production conditions must be studied before widespread commercial use.Objectives:The effects of light, temperature, KNO3, and CO(NH2)2 on beta-carotene and biomass accumulation were compared and evaluated in order to provide scientific guidance for commercial algal production in northeastern Thailand.Materials and Methods:An orthogonal design was used for evaluating optimal conditions for the algal production of three candidate Dunaliella salina strains (KU XI, KU 10 and KU 31) which were isolated from saline soils and cultured in the column photobioreactor.Results:The optimal light and temperature for algae growth were 135.3 μmol m-2 s-1 and 22°C, while the conditions of 245.6 μmol m-2 s-1 and 22°C induced the highest level of beta-carotene production (117.99 mg L-1). The optimal concentrations of KNO3, CO(NH2)2, and NaHCO3 for algae growth were 0.5 g L-1, 0.36 g L-1, and 1.5 g L-1, respectively, while 0, 0.12 g L-1 and 1.5 g L-1 were best suited for beta-carotene accumulation. The highest beta-carotene rate per cell appeared with the highest light intensity (12.21 pg) and lowest temperature (12.47 pg), and the lowest total beta-carotene content appeared at the lowest temperature (15°C). There was not a significant difference in biomass accumulation among the three Dunaliella strains; however, the beta-carotene accumulation of KU XI was higher than that of the other two strains.Conclusions:Light and temperature were both relevant factors that contributed to the growth and beta-carotene accumulation of the three D. salina strains, and NaHCO3 had significantly positive effects on growth. The degree of impact of the different factors on cell growth was temperature > NaHCO3 > light intensity > KNO3 > CO (NH2)2 > strains; the impact on beta-carotene accumulation was temperature > light intensity > KNO3 > CO (NH2)2 > strains > NaHCO3

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Bacterial spot (BS), incited by Xanthomonas campestris pv. vesicatoria (Xcv), is one of the most serious diseases of pepper. For a comparative analysis of defense responses to Xcv infection, we performed a transcriptomic analysis of a susceptible cultivar, ECW, and a resistant cultivar, VI037601, using the HiSeqTM 2500 sequencing platform. Approximately 120.23 G clean bases were generated from 18 libraries. From the libraries generated, a total of 38,269 expressed genes containing 11,714 novel genes and 11,232 differentially expressed genes (DEGs) were identified. Functional enrichment analysis revealed that the most noticeable pathways were plant-pathogen interaction, MAPK signaling pathway—plant, plant hormone signal transduction and secondary metabolisms. 1,599 potentially defense-related genes linked to pattern recognition receptors (PRRs), mitogen-activated protein kinase (MAPK), calcium signaling, and transcription factors may regulate pepper resistance to Xcv. Moreover, after Xcv inoculation, 364 DEGs differentially expressed only in VI037601 and 852 genes in both ECW and VI037601. Many of those genes were classified as NBS-LRR genes, oxidoreductase gene, WRKY and NAC transcription factors, and they were mainly involved in metabolic process, response to stimulus and biological regulation pathways. Quantitative RT-PCR of sixteen selected DEGs further validated the RNA-seq differential gene expression analysis. Our results will provide a valuable resource for understanding the molecular mechanisms of pepper resistance to Xcv infection and improving pepper resistance cultivars against Xcv.

To evaluate the potential of algal biotechnology to replace traditional agriculture in northeastern Thailand, an open raceway cultivation system was developed to produce biomass and beta-carotene. Dunaliella salina KU 11 isolated from local saline soil was cultured in open raceway tanks using brine and saline lake water. Grown in modified Johnson's medium (with 2-3.5 M NaCl), the algae reached a maximum cell density on the fourth day (1.8 × 10 cells mL ). Increasing KNO and NaHCO from 0.5 and 0.043 g L to 1 and 2.1 g L , respectively, significantly improved the yields of biomass (0.33 g L ) and beta-carotene (19 mg L ). Expected profits for algal production were evaluated, and it was found that this strain was suitable for outdoor cultivation and the developing algal industry in northeastern Thailand could produce high economic benefits (at least $64,120 per year per 0.16 ha).

An isolated <em>Dunaliella salina</em> strain from northern Thailand was cultured in modified Johnson’s medium in column photobioreactor. The beta-carotene accumulation mainly depended on the quantities of cells entering into carotenogenesis condition that was significantly enhanced by high started KNO3 concentration. Low remaining nitrate concentration in the culture of each cell (RNCC) was suitable for algae to accumulate beta-carotene. Following the cultivation time extended, RNCC of all cultures decreased and tended to the same level (10-20 pg/cell) although the biomass or betacarotene content in the culture was higher in high started KNO3 concentration. High light intensity restrained the growth especially in low KNO3 concentration but improved betacarotene accumulation and RNCC. The highest biomass and beta-carotene dry weight (DW) were 2.25 g L-1 and 79.2 mg g-1 DW respectively. Above results indicated that increasing the biomass and as early as possible to strengthen the stress on each cell was important to improve the final beta-carotene yield.

Dunaliella salina is an important microalga for β-carotene production. In Thailand, the D. salina has not been commercially cultivated. Aim of this study was to screen high β-carotene producing mutants. D. salina KU11 cells were radiated with 0.4 mmol photons m-2 •s-1 UV-C for 22 min. After 3 weeks, colonies which survived after radiation were allowed to grow on agar plates; fifty colonies out of 19,720 UV-mutagenized strains turned to orange. These colonies were picked up and transfer to modified Johnson medium. Four mutants out of fifty were KU5, KU18, KU20 and KU37 significantly produced high β-carotene at the stationary phase approximately up to 1.62, 2.03, 1.32 and 1.21 folds, respectively, compared to the wild type strain. In all three consecutive cycles of cultivation, the mutant KU18 accumulated 2.4-8.5 folds β-carotene (µg/ml) and 2.1-4.8 folds β-carotene (pg/cell) higher than the wild type, whereas cell density of the mutant KU18 was not different from the wild type. This is the new record of b-carotene producing mutant isolated from saline soil in Thailand.