Plant J| 南京农大徐国华团队揭示ADP-葡萄糖焦磷酸化酶的两个亚基OsAGPL1和OsAGPS1调节水稻磷的动态平衡

植物对磷(PI)饥饿胁迫的适应反应包括碳水化合物(即糖和淀粉)的积累。然而，内源碳水化合物的变化是否会反过来影响植物对磷的饥饿反应还没有得到广泛的研究。本研究对水稻ADP-葡萄糖焦磷酸化酶(AGP)大亚基和小亚基的编码基因--AGP大亚基1(AGPL1)和AGP小亚基1(AGPS1)在维持磷(P)动态平衡和磷饥饿信号调控方面进行了功能特性的研究，其中AGP大亚基1(AGPL1)和AGP小亚基1(AGPS1)是水稻ADP-葡萄糖焦磷酸化酶(AGP)大亚基和小亚基的编码基因。AGPL1和AGPS1均对氮(N)或磷(PI)缺乏有正反应，除根分生组织和成熟区外，几乎在所有组织中都有表达。AGPL1和AGPS1在叶绿体中发生物理相互作用，并催化淀粉生物合成的限速步骤。与野生型植株相比，agpl1、agps1和apgl1agps1突变体降低了低氮(LN)和低磷(LP)诱导的叶片淀粉积累。相反，AGPL1和/或AGPS1突变导致对照和LN条件下的叶鞘和根中主要糖、蔗糖含量增加。此外，在对照和LN条件下，突变体的PI积累增加，而在LP条件下，突变体的PI积累没有增加。值得注意的是，LN诱导的抑制PI积累的作用被归因于AGPL1和/或AGPS1的突变。此外，PI积累的增加伴随着OsSPX2的特异性抑制和几个PI转运蛋白基因的激活。这些结果表明，碳水化合物的平衡水平对于维持植物磷的动态平衡是至关重要的。

Plant acclimatory responses to phosphate (Pi) starvation stress include the accumulation of carbohydrates, namely sugar and starch. However, whether altered endogenous carbohydrate profile could in turn affect plant Pi starvation responses remains widely unexplored. Here, two genes encoding the large and small subunits of an ADP‐glucose pyrophosphorylase (AGP) in rice (Oryza sativa), AGP Large Subunit 1 (AGPL1) and AGP Small Subunit 1 (AGPS1), were functionally characterized with regard to maintenance of phosphorus (P) homeostasis and regulation of Pi starvation signaling. AGPL1 and AGPS1 were both positively responsive to nitrogen (N) or Pi deprivation, and expressed in almost all the tissues except in the meristem and mature zones of root. AGPL1 and AGPS1 physically interacted in chloroplast, and catalyzed the rate‐limiting step of starch biosynthesis. Low‐N‐ (LN) and low‐Pi (LP)‐triggered starch accumulation in leaves was impaired in agpl1, agps1 and apgl1 agps1 mutants compared with the wild‐type plants. By contrast, mutation of AGPL1 and/or AGPS1 led to an increase in the content of the major sugar, sucrose, in leaf sheath and root under control and LN conditions. Moreover, the Pi accumulation was enhanced in the mutants under control and LN conditions, but not LP conditions. Notably, the LN‐induced suppression of Pi accumulation was compromised attributed to the mutation of AGPL1 and/or AGPS1. Furthermore, the increased Pi accumulation was accompanied by the specific suppression of OsSPX2 and activation of several Pi transporter genes. These results indicate that a balanced level of carbohydrates is vital for maintaining plant P homeostasis.

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