Jiang Cizhong, Gu Jianying, Chopra Surinder, Gu Xun, Peterson Thomas
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011, USA.
Gene. 2004 Feb 4;326:13-22. doi: 10.1016/j.gene.2003.09.049.
Myb domain proteins contain a conserved DNA-binding domain composed of one to four conserved repeat motifs. In animals, Myb proteins are encoded by a small gene family and commonly contain three repeat motifs (R1R2R3); whereas, plant Myb proteins are encoded by a very large and diverse gene family in which a motif containing two repeats (R2R3) is the most common. In contrast to the conservation in the Myb domain, other regions of Myb proteins are highly variable. To explore the evolutionary origin of Myb genes, we cloned and sequenced Myb domains from maize and sorghum, and conducted a comprehensive phylogenetic analysis of Myb genes. The results indicate that the origins of individual Myb repeats are strikingly distinct, and that the R2 repeat has evolved more slowly than the R1 and R3 repeats. However, it is not clear which repeat is the most ancient one. The evidence also suggests that R2R3 and R1R2R3 Myb genes co-existed in eukaryotes before the divergence of plants and animals. Based on our results, we propose that R1R2R3 Myb genes were derived from R2R3 Myb genes by gain of the R1 repeat through an ancient intragenic duplication; this gain model is more parsimonious than the previous proposal that R2R3 Myb genes were derived from R1R2R3 Mybs by loss of the R1 repeat. A separate group of diverse non-typical Myb proteins exhibits a polyphyletic origin and a complex evolutionary pattern. Finally, a small group of ancient Myb paralogs prior to the amplification of current Myb genes is identified. Together, these results support a new model for the ordered evolution of Myb gene family.
Myb结构域蛋白含有一个由一到四个保守重复基序组成的保守DNA结合结构域。在动物中，Myb蛋白由一个小基因家族编码，通常包含三个重复基序（R1R2R3）；而植物Myb蛋白由一个非常庞大且多样的基因家族编码，其中包含两个重复基序（R2R3）的基序最为常见。与Myb结构域的保守性不同，Myb蛋白的其他区域高度可变。为了探索Myb基因的进化起源，我们从玉米和高粱中克隆并测序了Myb结构域，并对Myb基因进行了全面的系统发育分析。结果表明，各个Myb重复基序的起源明显不同，并且R2重复基序的进化速度比R1和R3重复基序慢。然而，尚不清楚哪个重复基序是最古老的。证据还表明，在动植物分化之前，R2R3和R1R2R3 Myb基因在真核生物中就已共存。基于我们的结果，我们提出R1R2R3 Myb基因是通过古老的基因内重复获得R1重复基序而从R2R3 Myb基因衍生而来的；这种获得模型比之前提出的R2R3 Myb基因是通过丢失R1重复基序而从R1R2R3 Myb基因衍生而来的说法更为简约。一组不同的非典型Myb蛋白表现出多系起源和复杂的进化模式。最后，鉴定出了一小群在当前Myb基因扩增之前的古老Myb旁系同源基因。总之，这些结果支持了Myb基因家族有序进化的新模型。
