Lahiri S D, Allison L A
Department of Biochemistry, University of Nebraska, N258 Beadle Center, Lincoln, Nebraska 68588-0664, USA.
Plant Physiol. 2000 Jul;123(3):883-94. doi: 10.1104/pp.123.3.883.
The eubacterial-like RNA polymerase of plastids is composed of organelle-encoded core subunits and nuclear-encoded sigma-factors. Families of sigma-like factors (SLFs) have been identified in several plants, including maize (Zea mays) and Arabidopsis. In vitro import assays determined that at least two of the maize sigma-like proteins have functional chloroplast transit peptides and thus are likely candidates for chloroplast transcriptional regulators. However, the roles of individual SLFs in chloroplast transcription remain to be determined. We have raised antibodies against the unique amino-terminal domains of two maize SLFs, ZmSig1 and ZmSig3, and have used these specific probes to examine the accumulation of each protein in different maize tissues and during chloroplast development. The expression of ZmSig1 is tissue specific and parallels the light-activated chloroplast development program in maize seedling leaves. Its accumulation in mature chloroplasts however, is not affected by subsequent changes in the light regime. It is interesting that the expression profile of ZmSig3 is complementary to that of ZmSig1. It accumulates in non-green tissues, including roots, etiolated seedling leaves, and the basal region of greening seedling leaves. The nonoverlapping expression patterns of these two plastid-localized SLFs suggest that they may direct differential expression of plastid genes during chloroplast development.
质体中类似真细菌的RNA聚合酶由细胞器编码的核心亚基和核编码的sigma因子组成。在包括玉米（Zea mays）和拟南芥在内的几种植物中已经鉴定出了类似sigma因子（SLF）的家族。体外导入实验确定，至少两种玉米类似sigma的蛋白具有功能性叶绿体转运肽，因此很可能是叶绿体转录调节因子的候选者。然而，单个SLF在叶绿体转录中的作用仍有待确定。我们已经制备了针对两种玉米SLF（ZmSig1和ZmSig3）独特氨基末端结构域的抗体，并使用这些特异性探针来检测每种蛋白在不同玉米组织以及叶绿体发育过程中的积累情况。ZmSig1的表达具有组织特异性，并且与玉米幼苗叶片中光激活的叶绿体发育程序平行。然而，它在成熟叶绿体中的积累不受随后光照条件变化的影响。有趣的是，ZmSig3的表达谱与ZmSig1互补。它在非绿色组织中积累，包括根、黄化幼苗叶片和绿化幼苗叶片的基部区域。这两种定位于质体的SLF不重叠的表达模式表明，它们可能在叶绿体发育过程中指导质体基因的差异表达。
