Huang S, An Y Q, McDowell J M, McKinney E C, Meagher R B
Department of Genetics, University of Georgia, Athens 30602, USA.
Plant J. 1996 Aug;10(2):189-202. doi: 10.1046/j.1365-313x.1996.10020189.x.
Plants contain complex actin gene families composed of several diverse and ancient subclasses of genes. One Arabidopsis actin gene subclass represented by the ACT4 and ACT12 genes has been isolated and characterized. Both actin genes have typical plant actin gene structures, including three small introns interrupting the coding region and an intron within the mRNA leader. Their encoded proteins differ from each other in only one amino acid, whereas they differ in 3-10% of their amino acids from the other five Arabidopsis actin subclasses. They also share a few small blocks of DNA sequence homology in the 5' flanking region near their TATA boxs, but not in their introns, 3' flanking regions, or degenerate positions within codons. Southern analysis with gene-specific probes from 5' flanking sequences showed that both were single copy genes in the genome. Both RNA gel blot analysis with 3' gene-specific probes and reverse transcriptase-mediated polymerase chain reactions (RT-PCR) with gene-specific primers detected low levels of ACT4 and ACT12 mRNAs in flowers and very high levels in pollen. The RT-PCR detected very low levels of these mRNAs in the vegetative organs. The 5' region from both genes, including the promoter region, TATA box, the sequence for the mRNA leader and its intron, and the first 19 actin codons, was fused to a beta-glucuronidase (GUS) reporter gene. Expression of the GUS fusions were examined histochemically in 40 independent transgenic Arabidopsis plants. Expression of the ACT4/GUS fusion was restricted to young vascular tissues, tapetum, and developing and mature pollen. Similar expression patterns in these tissues and cell types were observed for ACT12/GUS fusion, yet unlike ACT4, ACT12 was also strongly expressed in the root cap and in a ring of pericycle tissues during lateral root initiation and early development. The unique expression patterns of the ACT4/ACT12 actin gene subclass are discussed in light of recent data on the other expressed members of the Arabidopsis actin gene family.
植物含有由几个不同的古老基因亚类组成的复杂肌动蛋白基因家族。一个以ACT4和ACT12基因代表的拟南芥肌动蛋白基因亚类已被分离和鉴定。这两个肌动蛋白基因都具有典型的植物肌动蛋白基因结构，包括打断编码区的三个小内含子以及mRNA前导序列中的一个内含子。它们编码的蛋白质彼此仅在一个氨基酸上不同，而与其他五个拟南芥肌动蛋白亚类的氨基酸差异为3% - 10%。它们在靠近其TATA框的5'侧翼区域也共享一些小的DNA序列同源块，但在内含子、3'侧翼区域或密码子内的简并位置则没有。用来自5'侧翼序列的基因特异性探针进行的Southern分析表明，二者在基因组中均为单拷贝基因。用3'基因特异性探针进行的RNA凝胶印迹分析以及用基因特异性引物进行的逆转录酶介导的聚合酶链反应（RT-PCR）均检测到花中ACT4和ACT12 mRNA水平较低，而在花粉中水平非常高。RT-PCR检测到营养器官中这些mRNA的水平非常低。将这两个基因的5'区域，包括启动子区域、TATA框、mRNA前导序列及其内含子的序列以及前19个肌动蛋白密码子，与β-葡萄糖醛酸酶（GUS）报告基因融合。在40株独立的转基因拟南芥植株中通过组织化学方法检测了GUS融合体的表达。ACT4/GUS融合体的表达局限于幼嫩维管组织、绒毡层以及发育中和成熟的花粉。ACT12/GUS融合体在这些组织和细胞类型中观察到类似的表达模式，但与ACT4不同的是，ACT12在侧根起始和早期发育期间的根冠以及一圈中柱鞘组织中也强烈表达。根据拟南芥肌动蛋白基因家族其他表达成员的最新数据，对ACT4/ACT12肌动蛋白基因亚类的独特表达模式进行了讨论。
