RUI: Beta-amylases and transitory starch metabolism in Arabidopsis leaves

淀粉是植物重要的能量储存化合物，它构成了人类饮食的重要组成部分。 在叶片中，淀粉在白天积累在叶绿体中，并在夜间分解，当光合作用不可能时为植物提供能量。 负责在夜间分解大部分淀粉的酶是-淀粉酶（BAM）。 在拟南芥基因组中有9个BAM或BAM样基因，其中6个（BAM 1、BAM-2、BAM-3、BAM-4、BAM-6和BAM-9）编码靶向叶绿体的蛋白。 其中，只有BAM 1、BAM-2、BAM-3和BAM-6具有催化活性。 这项工作的重点是BAM 9，它位于叶绿体中，但没有催化活性。 缺乏BAM 9的突变体及其结构和表达模式的初步证据表明，它可能在调节淀粉代谢中发挥作用。 本工作的三个目标是1）研究BAM 9对缺乏蛋白质的突变体的叶提取物中的四种活性质体BAM的昼夜活性的影响，2）表征纯BAM 9结合淀粉和各种小碳水化合物的能力，以及3）鉴定和表征结合BAM 9的蛋白质。 据推测，当淀粉降解正常停止时，BAM 9在黎明起抑制一种或多种活性BAM的活性的作用。 这项研究将有助于表征拟南芥中5种质体靶向的淀粉酶的生理功能，并将揭示叶片中淀粉代谢是如何调节的，特别是在夜间/白天的转换。 该项目还将培训一些计划从事科学职业的本科生，以及一名计划在以本科为主的机构从事教学/研究的博士后学者。

Starch is an important energy-storage compound for plants and it makes up a significant portion of the human diet. In leaves, starch accumulates in chloroplasts during the day, and is broken down at night to provide energy for the plant when photosynthesis is not possible. The enzyme responsible for breaking down most of the starch at night is β-amylase (BAM). There are nine BAM or BAM-like genes in the Arabidopsis genome, six of which (BAM 1, -2, -3, -4, -6 and -9) encode proteins that are targeted to chloroplasts. Of these, only BAM1, -2, -3, and -6 are catalytically active. The focus of this work is on BAM9, which is located in chloroplasts but is catalytically inactive. Preliminary evidence from a mutant lacking BAM9, and from its structure and pattern of expression, suggests that it might play a role in regulating starch metabolism. The three objectives of this work are to 1) investigate the influence of BAM9 on the diurnal activity of the four active plastidic BAMs in leaf extracts of mutants lacking the proteins, 2) characterize the ability of pure BAM9 to bind starch and various small carbohydrates, and 3) identify and characterize protein(s) that bind to BAM9. It is hypothesized that BAM9 acts to inhibit the activity of one or more of the active BAMs at dawn when starch degradation normally stops. This research will help to characterize the physiological functions of five plastid-targeted β-amylases in Arabidopsis, and will shed light on how starch metabolism is regulated in leaves, especially at the night/day transition. The project will also train a number of undergraduates planning to pursue careers in science, and a teaching/research postdoctoral scholar planning to pursue a career at a predominantly undergraduate institution.