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(GPAT) in Rice - Journal of Integrative Plant Biology

(GPAT) in Rice - Journal of Integrative Plant Biology

information on squash GPAT determined by X-ray crystallography at 1.55 Ǻ 79 80 81 82 83 84 85 86 87 88 89 90 91 The rice plants (Oryza sativa) are cultivated mainly in tropical and subtropical regions and their distribution are primarily governed by temperature. During the rice life cycle, the chilling-sensitive stages are the seedling and the early microspore stage of pollen development (Shimono et al. 2002, Zhu et al. 2008). If the rice seedlings are exposed to low temperature, growth is inhibited and there is a failure of ripening at grain filling period (Shimono et al. 2002). Thus, an improvement in the tolerance of rice plants to chilling temperature has long been desired. The relationship between chilling sensitivity and PGs in rice plants had been reported (Zhu et al. 2008). Alteration of the fatty acid composition of PGs by genetic engineering would plausibly confer chilling tolerance on rice plants. The relationship between amino acid sequence and substrate selectivity of GPAT was elucidated by creating chimeric Goats between squash (Cucurbita moscata, chilling-sensitive) and spinach (Spinacea oleracea, chilling-tolerant) and the results were interpreted using structural 92 93 94 95 96 97 98 99 100 101 102 103 104 resolution (Slabas et al. 2002). The chimeric GPATs containing the spinach region from residues 128 to 187 prefer the 18:1 unsaturated fatty acid rather than 16:0 saturated fatty acid. Analysis of the chimeric GPAT structure suggests that the size and character of the cavity (binding sites of substrate acyl chains) that is formed from this region determines the specific recognition of acyl chains (Tamada et al. 2004). In this experiment, chill-sensitive rice (Oryza sativa Japonica Group cultivar Zihui-100 and Oryza sativa Indica Group cultivar Shanyou-63), maize (Zea mays), squash (Cucurbita moschata), cucumber (Cucumis sativus) plants, and chill-resistant spinach (spinacia oleracea), Arabidopsis thaliana and horsebean (Vicia faba) plants, total 8 materials of 7 plant species were used. The aims of the study were to explore 1) selective and non-selective GPATs performed under physiological relevant conditions by 14 C and 3 H isotope; 2) molecular basis of non-selective (rice, squash, maize and 4

eaction mixture, [ 14 C]-16:0-ACP and [ 3 H]-18:1-ACP at a concentration of 1.1 μ 105 106 107 cucumber) GPATs versus selective (spinach, arabidopsis thaliana and horsebean) ones by 3D structure alignment, resulting in a possible approach to alteration of selectivity of rice GPAT enzyme. 108 109 110 111 112 113 114 115 Results Analysis of substrate selectivity of GPAT enzyme In vitro substrate selectivity assays performed under physiologically relevant conditions have been established that discriminate between selective and non-selective forms of the enzyme. Two different pH values were used, pH 7.4 and pH 8.0, reflecting the pH of the chloroplast in the dark and the light respectively. Assays were performed under competitive conditions with two substrates in the 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 mol/L each, which was close to their physiological concentration. The glycerol-3-phosphate (G-3-P) concentration was μ 300 mol/L, which was in the physiological range of this substrate. Glycerol-3-phosphate acyltransferases catalyze the acylation of the sn-1 position of glycerol 3-phosphate using acyl-acyl carrier proteins (acyl-ACPs) as the physiological acyl donor for the reaction (Murata et al. 1997). Figure 1 showed that GPATs could either be selective, preferentially using the unsaturated fatty acid, oleic acid (18:1), as the acyl donor, or nonselective, using either oleic acid (18:1) or the saturated fatty acid, palmitic acid (16:0), at comparable rates. As a result, both 16:0-lysophosphatidic acid (16:0-LPA) and 18:1-lysophosphatidic acid (18:1-LPA) in reaction system were the products catalyzed by glycerol- 3-phosphate acyl transferase (GPAT) between substrate 1, glycerol-3-phosphate, and substrate 2, either 16:0-ACP or 18:1-ACP. Experiment results showed that substrate selectivity of the GPAT played a strong influence on molecular species of the lysophosphatidic acid (18:1-LPA or 16:0-LPA) accumulated 5

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