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首页> 外文期刊>Journal of Experimental Botany >Maize leaf PPDK regulatory protein isoform-2 is specific to bundle sheath chloroplasts and paradoxically lacks a Pi-dependent PPDK activation activity
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Maize leaf PPDK regulatory protein isoform-2 is specific to bundle sheath chloroplasts and paradoxically lacks a Pi-dependent PPDK activation activity

机译：玉米叶PPDK调节蛋白同种型-2特异于束鞘叶片，矛盾缺乏PI依赖性PPDK活化活性

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摘要

In the maize C-4 pathway, PDRP1 is known to regulate C-4 PPDK activity in mesophyll chloroplasts. A second PDRP isoform, PDRP2, is shown to be the apparent regulator of C-4 PPDK in bundle sheath chloroplasts.In C-4 plants, the pyruvate phosphate dikinase regulatory protein (PDRP) regulates the C-4 pathway enzyme pyruvate phosphate dikinase (PPDK) in response to changes in incident light intensity. In maize (Zea mays) leaves, two distinct isoforms of PDRP are expressed, ZmPDRP1 and ZmPDRP2. The properties and C-4 function of the ZmPDRP1 isoform are well understood. However, the PDRP2 isoform has only recently been identified and its properties and function(s) in maize leaves are unknown. We therefore initiated an investigation into the maize PDRP2 isoform by performing a side by side comparison of its enzyme properties and cell-specific distribution with PDRP1. In terms of enzyme functionality, PDRP2 was found to possess the same protein kinase-specific activity as PDRP1. However, the PDRP2 isoform was found to lack the phosphotransferase activity of the bifunctional PDRP1 isoform except when PDRP2 in the assays is elevated 5- to 10-fold. A primarily immuno-based approach was used to show that PDRP1 is strictly expressed in mesophyll cells and PDRP2 is strictly expressed in bundle sheath strand cells (BSCs). Additionally, using in situ immunolocalization, we establish a regulatory target for PDRP2 by showing a significant presence of C-4 PPDK in BSC chloroplasts. However, a metabolic role for PPDK in this compartment is obscure, assuming PPDK accumulating in this compartment would be irreversibly inactivated each dark cycle by a monofunctional PDRP2.
机译：在玉米C-4途径中，已知PDRP1调节叶片叶绿体中的C-4 PPDK活性。第二PDRP同种型PDRP2，PDRP2被显示为C-4 PPDK的束鞘叶片中的表观稳定剂。在C-4植物中，丙酮酸磷酸酯Dikinase调节蛋白（PDRP）调节C-4途径酶磷酸丙酮酸二磷酸酯（ PPDK）响应入射光强度的变化。在玉米（Zea Mays）叶中，表达了两个不同的PDRP同种型，ZMPDRP1和ZMPDRP2。 ZMPDRP1同种型的特性和C-4功能得到了很好的理解。然而，PDRP2同种型才识别出来，并且其在玉米叶中的性质和功能是未知的。因此，我们通过用PDRP1的酶特性和细胞特异性分布进行了通过对玉米PDRP2同种型进行了调查。就酶官能度而言，发现PDRP2具有与PDRP1相同的蛋白激酶特异性活性。然而，发现PDRP2同种型缺乏双官能PDRP1同种型的磷酸转移酶活性，除非测定中的PDRP2升高5-10倍。使用主要基于免疫的方法来表明PDRP1严格表达在叶片细胞中，并且PDRP2在束鞘链细胞（BSC）中严格地表达。另外，使用原位免疫胶质化，我们通过在BSC叶绿体中显示C-4 PPDK的显着存在来建立PDRP2的调节靶标。然而，假设在该隔室中的PPDK积累的PPDK，PPDK在该隔室中的代谢作用是模糊的，这将通过单官能PDRP2不可逆转地灭活每个暗循环。

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