Molecular and genetic anaysis of the AS2 gene that is involved in the formation of bilateral symmetric leaf lamin

拟南芥（Arabidopsis thaliana）的不对称叶片2 （ASYMMETRIC LEAVES2, AS2）基因参与了叶脉系统的建立，包括叶脉突出的中脉，以及对称叶片的发育。该基因产物还能抑制叶片中1类knox同源盒基因的表达。我们已经对AS2基因进行了表征，该基因似乎编码了一种具有半胱氨酸重复序列（指定为c基序）的新蛋白质，并且在初级序列的氨基末端有亮氨酸拉链状序列。拟南芥基因组包含42个假定的基因，这些基因可能编码具有保守氨基酸和序列的蛋白质，其中包括c基序和氨基末端的亮氨酸-拉链样序列。因此，AS2蛋白属于一个新的蛋白家族，我们将其命名为AS2家族。该家族除AS2外的其他成员也被命名为asl （AS2样蛋白）。AS2转录本主要位于子叶原基的近轴结构域。绿色荧光蛋白融合的AS2集中在植物细胞核中。转基因拟南芥植株过表达AS2 cDNA导致叶片向上卷曲，这与AS2功能缺失突变产生的叶片向下卷曲明显不同。我们的研究结果表明，AS2在植物细胞核中参与某种基因的转录，从而控制对称扁平叶面的形成和突出的中脉的建立以及其他脉络模式。

The ASYMMETRIC LEAVES2 (AS2) gene of Arabidopsis thaliana is involved in the establishment of the leaf venation system, which includes die prominent midvein, as well as in the development of a symmetric lamina. The gene product also represses the expression of class 1 knox homeobox genes in leaves. We have characterized the AS2 gene, which appears to encode a novel protein with cysteine repeats (designated the C-motif) and a leucine-zipper-like sequence in the amino-terminal half of the primary sequence. The Arabidopsis genome contains 42 putative genes that potentially encode proteins with conserved amino and sequences that include the C-motif and the leucine-zipper-like sequence in the amino-terminal half. Thus, the AS2 protein belongs to a novel family of proteins that we have designated the AS2 family. Members of this family except AS2 also have been designated ASLs (AS2-like proteins). Transcripts of AS2 were detected mainly in adaxial domains of cotyledonary primordia. Green fluorescent protein-fused AS2 was concentrated in plant cell nuclei. Overexpression of AS2 cDNA in transgenic Arabidopsis plants resulted in upwardly curled leaves, which differed markedly from the downwardly curled leaves generated by loss-of-function mutation of AS2. Our results suggest that AS2 functions in the transcription of a certain gene(s) in plant nuclei and thereby controls the formation of a symmetric flat leaf lamina and the establishment of a prominent midvein and other patterns of venation.