Members of basic helix-loop-helix (bHLH) gene family found in all eukaryotes play crucial roles in response to stress. Though, most eukaryotes carry the proteins of this family, biological functions of the most bHLH family members are not deeply evaluated in plants. In this study, we conducted a comprehensive genome-wide analysis of bHLH transcription factors in salt tolerant common bean. We identified 155 bHLH protein-encoding genes (PvbHLH) by using in silico comparative genomics tools. Based on the phylogenetic tree, PvbHLH genes were classified into 8 main groups with 21 subfamilies. Exon-intron analysis indicated that proteins belonging to same main groups exhibited a closely related gene structure. While, the PvbHLH gene family has been mainly expanded through segmental duplications, a total of 11 tandem duplication were detected. Genome-wide expression analysis of bHLH genes showed that 63 PvbHLH genes were differentially expressed in at least one tissue. Three of them displayed higher expression values in both leaf and root tissues. The in silico micro-RNA target transcript analyses revealed that totally 100 PvHLH genes targeted by 86 plant miRNAs. The most abundant transcripts, which were targeted by all 18 plant miRNA, were belonging to PvHLH-22 and PvHLH-44 genes. The expression of 16 PvbHLH genes in the root and leaf tissues of salt-stressed common bean was evaluated using qRT-PCR. Among them, two of PvbHLHs, PvbHLH-54, PvbHLH-148, were found to be up-regulated in both tissues in correlation with RNA-seq measurements. The results of this study could help improve understanding of biological functions of common bean bHLH family under salt stress. Additionally, it may provide basic resources for analyzing bHLH protein function for improving economic, agronomic and ecological benefit in common bean and other species.

IntroductionMelon (Cucumis melo L.), an annual diploid plant, is an economically important horticultural crop grown in temperate, subtropical, and tropical regions worldwide. With a total production of 1.7 million tons, Turkey was the second biggest producer after China in 2009. Like many other fruits melon fruits provide a good source of potassium and vitamin C. They are also fat and cholesterol free, high in water content, and are relatively low in calories. Moreover, melons may have an anticlotting action and are also thought to lower cancer and heart disease risk (Lester, 1996).Biotic and abiotic stresses are the most important factors that severely limit plant growth and metabolism (Makbul et al., 2011). Abiotic stress is the primary cause of crop loss worldwide, reducing average yields for most major crop plants by more than 50% (Bray et al., 2000). Moreover, when the usable areas on the earth are classified in view of stress factors, drought stress is one of the most widespread environmental stresses (Arora et al., 2002;Saruhan Güler et al., 2012). Although each stress factor produces its own specific effect on plants, in general all stress conditions can cause an increase in reactive oxygen species (ROS). ROS are recognized as detrimental to biological systems because they cause the oxidation of lipids, proteins, deoxyribonucleic acid, and carbohydrates. Ultimately, toxic levels of ROS cause a chain reaction of cellular oxidation, which results in unhealthy situations and lethality. In addition to the oxidative stress related production, ROS are an inevitable outcome of normal physiological processes, such as glycolysis and photosynthesis (Mittler et al., 2004). Plant antioxidant systems, both enzymatic and nonenzymatic, play an important role in balancing and preventing oxidative damage (Foyer et al., 1994;Baysal Furtana and Tıpırdamaz, 2010). Nonenzymatic antioxidant metabolites include anthocyanin, flavonoids, carotenoids, α-tocopherol, ascorbate (AsA), and reduced glutathione (GSH) (Halliwell, 1987); enzymatic antioxidants consist of superoxide dismutase (

Overcoming the recalcitrance in lignocellulosic biomass for efficient hydrolysis of the polysaccharides cellulose and hemicellulose to fermentable sugars is a research priority for the transition from a fossilfuel-based economy to a renewable carbohydrate economy. Methylglucuronoxylans (MeGXn) are the major components of hemicellulose in woody biofuel crops. Here, we describe efficient production of the GH10 xylanase Xyl10B from Thermotoga maritima in transplastomic plants and demonstrate exceptional stability and catalytic activities of the in planta produced enzyme. Fully expanded leaves from homotransplastomic plants contained enzymatically active Xyl10B at a level of 11-15% of their total soluble protein. Transplastomic plants and their seed progeny were morphologically indistinguishable from non-transgenic plants. Catalytic activity of in planta produced Xyl10B was detected with poplar, sweetgum and birchwood xylan substrates following incubation between 40 and 90 °C and was also stable in dry and stored leaves. Optimal yields of Xyl10B were obtained from dry leaves if crude protein extraction was performed at 85 °C. The transplastomic plant derived Xyl10B showed exceptional catalytic activity and enabled the complete hydrolysis of MeGXn to fermentable sugars with the help of a single accessory enzyme (α-glucuronidase) as revealed by the sugar release assay. Even without this accessory enzyme, the majority of MeGXn was hydrolyzed by the transplastomic plant-derived Xyl10B to fermentable xylose and xylobiose.

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Two cultivars of peanut (Arachis hypogaea L.) which were designated as resistant (Florispan) and sensitive (Gazipasa) according to their growth retardation under drought stress conditions were compared for their oxidative damage and antioxidant responses. Sixteen days-old peanut seedlings were subjected to PEG-6000 solutions of two different osmotic potentials; -0.4 and -0.8 MPa, and various growth parameters, photosystem II activity, changes in malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and proline levels, activities of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX) and gluthatione reductase (GR) enzymes were determined. Both cultivars exhibited water deficit at -0.8 MPa osmotic potential of PEG-6000 and H 2 O 2 levels significantly increased during exposure to -0.4 MPa osmotic potential. However, H 2 O 2 levels were under control in both cultivars at exposure to -0.8 MPa osmotic potential. Significant proline accumulation was observed in the tissues of cv. Florispan at -0.8 MPa osmotic potential, whereas proline accumulation did not appear to be an essential part of the protection mechanism against drought in cv. Gazipasa. No significant variation in chlorophyll fluorescence values were detected in neither of the cultivars. Enzyme activity measurements revealed that Gazipasa copes well with lesser magnitudes of drought stress by increasing the activity of mainly APX, and during harsh stress conditions, only APX maintains its activity in the tissues. In cultivar Florispan, GR activity appears to take role in lesser magnitudes of drought stress, whereas CAT and APX activities appear to be very crucial antioxidative defenses during intense stress conditions. The results indicate that, the level of proline and activities of the enzymes CAT and APX are important mechanisms for the maintenance of drought tolerance in peanut plants.