Departamento de Ingeniería Genética, CINVESTAV, Unidad Irapuato, Km 9.8 Libramiento Norte, CP 36821 Irapuato, Guanajuato, Mexico.
Plant Mol Biol. 2012 Mar;78(4-5):377-92. doi: 10.1007/s11103-011-9871-0. Epub 2012 Jan 7.
Sucrose synthase (SUS) is a key enzyme of carbon metabolism in heterotrophic tissues of plants. The Arabidopsis genome contains six SUS genes. Two members of this family, namely AtSUS2 (At5g49190) and AtSUS3 (At4g02280) are strongly and differentially expressed in Arabidopsis seed. Expression analysis was carried out using SUS:promoter-GUS fusion lines in a wild-type genetic background or in a mutant carrying a lesion in the transcription factor LEAFY COTYLEDON 2 (LEC2; At1g28300). The accumulation patterns of mRNA, protein, and SUS activity were altered in the lec2 mutant during seed development 9-18 days after flowering. This indicates that LEC2 acts epistatically on the expression of AtSUS2 and AtSUS3. It appears that LEC2 is required for cotyledon-specific expression of both SUS genes but it is not responsible for expression in the radicle tip during embryo development. The AtSUS2 promoter was induced in planta by feeding of glucose but less so by sucrose and trehalose. Non-phosphorylable glucose analogs such as 3-O-methyl-glucose and 2-deoxyglucose also caused an induction, suggesting that sugar signaling proceeds by a hexokinase-independent pathway, possibly involving hexose sensing. Analysis of transgenic lines carrying of truncated versions of the AtSUS2:promoter fused to Beta-glucuronidase activity revealed an internal 421 bp region that was responsible for expression in seeds. Bioinformatic sequence analysis revealed regulatory cis-elements putatively responsible for the spatio-temporal pattern of AtSUS2 expression such as the SEF3 (aaccca) and W-box (ttgact) motifs. These findings are discussed in relation to the roles played by AtSUS2, AtSUS3 and LEC2 in the biosynthesis of seed storage products in Arabidopsis.
蔗糖合酶（SUS）是植物异养组织中碳代谢的关键酶。拟南芥基因组包含六个 SUS 基因。该家族的两个成员，即 AtSUS2（At5g49190）和 AtSUS3（At4g02280），在拟南芥种子中强烈且差异表达。在野生型遗传背景或携带转录因子 LEAFY COTYLEDON 2（LEC2；At1g28300）突变的突变体中，使用 SUS：启动子-GUS 融合系进行表达分析。在花后 9-18 天的种子发育过程中，lec2 突变体中的 mRNA、蛋白质和 SUS 活性的积累模式发生改变。这表明 LEC2 对 AtSUS2 和 AtSUS3 的表达起上位作用。似乎 LEC2 是两种 SUS 基因在子叶中特异性表达所必需的，但它不是胚胎发育过程中胚根尖端表达所必需的。AtSUS2 启动子在植物体内通过葡萄糖喂养诱导，但蔗糖和海藻糖诱导作用较弱。非磷酸化葡萄糖类似物，如 3-O-甲基葡萄糖和 2-脱氧葡萄糖，也引起诱导，表明糖信号通过己糖激酶非依赖性途径进行，可能涉及己糖感应。携带 AtSUS2：启动子与β-葡萄糖醛酸酶活性融合的截断版本的转基因系的分析显示，负责种子表达的内部 421 bp 区域。生物信息学序列分析揭示了潜在负责 AtSUS2 表达时空模式的调控顺式元件，如 SEF3（aaccca）和 W-box（ttgact）基序。这些发现与 AtSUS2、AtSUS3 和 LEC2 在拟南芥种子储存产物生物合成中的作用有关。
