Department of Agronomy and Plant Genetics, Plant Molecular Genetics Institute, University of Minnesota, St. Paul, Minnesota 55108.
Plant Physiol. 1992 Oct;100(2):958-64. doi: 10.1104/pp.100.2.958.
Amyloplasts in storage organs such as maize (Zea mays L.) endosperm are plastid-derived, nonphotosynthetic, starch-accumulating organelles. This study was initiated to characterize the plastid genome in maize endosperm cells containing differentiated amyloplasts and to determine whether plastid genes are transcribed during the period of amyloplast biogenesis in endosperm development. Four cosmid clones representing the total sequence diversity of the maize plastid genome were hybridized to restriction digests of total cellular DNA from isolated 16-day-old endosperms. The hybridization patterns indicated that the plastid DNA present in endosperm tissue was indistinguishable from that in leaf total DNA. Methylation of maize endosperm amyloplast DNA or leaf chloroplast DNA was not detected with the methylation-sensitive enzymes HpaII and EcoRII. Transcripts homologous to the 17 specific plastid DNA BamHI fragments tested were detectable in total RNA prepared from 16-day-old endosperm tissue. Compared with leaf transcripts, the abundance of endosperm transcripts was substantially lower for transcripts detected by 12 different BamHI fragments and was similar or relatively higher for some transcripts homologous to five BamHi fragments. Transcripts homologous to genes for plastid ribosomal small subunit proteins 7 and 12 on fragments 10 and 23 and to an open reading frame on fragment 14 accumulated primarily as unprocessed or partially processed species in endosperm RNA. The demonstration that maize endosperm cells contain an intact, transcriptionally active plastid genome indicates that plastid genes could contribute to amyloplast biogenesis, although no transcripts unique to endosperm were identified.
淀粉体在玉米（Zea mays L.）胚乳等贮藏器官中是由质体衍生而来的、非光合的、积累淀粉的细胞器。本研究旨在阐明含有分化淀粉体的玉米胚乳细胞中的质体基因组，并确定质体基因在胚乳发育过程中淀粉体生物发生期间是否转录。四个 cosmid 克隆代表了玉米质体基因组的总序列多样性，与从分离的 16 天龄胚乳中提取的总细胞 DNA 的限制酶切产物进行杂交。杂交模式表明，胚乳组织中的质体 DNA 与叶片总 DNA 无法区分。用甲基化敏感酶 HpaII 和 EcoRII 未检测到玉米胚乳淀粉体 DNA 或叶片叶绿体 DNA 的甲基化。在从 16 天龄胚乳组织中提取的总 RNA 中可以检测到与 17 个特定质体 DNA BamHI 片段同源的转录物。与叶片转录物相比，12 个不同 BamHI 片段检测到的转录物在胚乳转录物中的丰度要低得多，而与 5 个 BamHI 片段同源的一些转录物的丰度则相似或相对较高。在片段 10 和 23 上的质体核糖体小亚基蛋白基因 7 和 12 以及片段 14 上的一个开放阅读框的同源转录物主要以未加工或部分加工的形式在胚乳 RNA 中积累。玉米胚乳细胞含有完整的、转录活性的质体基因组，这表明质体基因可能有助于淀粉体的生物发生，尽管没有鉴定出仅存在于胚乳中的转录物。
