Soyano Takashi, Thitamadee Siripong, Machida Yasunori, Chua Nam-Hai
Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
Plant Cell. 2008 Dec;20(12):3359-73. doi: 10.1105/tpc.108.061796. Epub 2008 Dec 16.
ASYMMETRIC LEAVES2 (AS2)/LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family proteins are plant-specific nuclear proteins, and genes encoding several family members have been implicated in plant development. We investigated the function of two members of the Arabidopsis thaliana AS2/LBD family, AS2-LIKE19 (ASL19)/LBD30 and ASL20/LBD18, which encode homologous proteins. Both ASL19 and ASL20 were expressed in immature tracheary elements (TEs), and the expression was dependent on VASCULAR-RELATED NAC-DOMAIN PROTEIN6 (VND6) and VND7, which are transcription factors required for TE differentiation. Overexpression of ASL19 and ASL20 induced transdifferentiation of cells from nonvascular tissues into TE-like cells, similar to those induced upon VND6/7 overexpression. By contrast, aberrant TEs were formed when a cDNA encoding a fusion protein of ASL20 with an artificial repressor domain (ASL20-SRDX) was expressed from its native promoter. These results provide evidence that ASL proteins positively regulate TE differentiation. In transgenic plants overexpressing both ASL19 and ASL20, the xylem-deficient phenotype caused by the expression of dominant-negative versions of VND6/7 proteins was not rescued. However, ectopic expression of VND7 was detected in plants overexpressing ASL20. Moreover, VND genes and their downstream targets were downregulated in ASL20-SRDX plants. Therefore, ASL20 appears to be involved in a positive feedback loop for VND7 expression that regulates TE differentiation-related genes.
不对称叶片2（AS2）/侧生器官边界结构域（LBD）家族蛋白是植物特有的核蛋白，编码该家族多个成员的基因与植物发育有关。我们研究了拟南芥AS2/LBD家族的两个成员，即编码同源蛋白的AS2样19（ASL19）/LBD30和ASL20/LBD18的功能。ASL19和ASL20均在未成熟的管状分子（TE）中表达，且这种表达依赖于血管相关NAC结构域蛋白6（VND6）和VND7，它们是TE分化所需的转录因子。ASL19和ASL20的过表达诱导非维管组织细胞转分化为类TE细胞，类似于VND6/7过表达时诱导产生的细胞。相比之下，当从其天然启动子表达编码带有人工抑制结构域的ASL20融合蛋白（ASL20-SRDX）的cDNA时，会形成异常的TE。这些结果证明ASL蛋白正向调控TE分化。在同时过表达ASL19和ASL20的转基因植物中，由VND6/7蛋白的显性负性版本表达所导致的木质部缺陷表型未得到挽救。然而，在过表达ASL20的植物中检测到了VND7的异位表达。此外，VND基因及其下游靶标在ASL20-SRDX植物中表达下调。因此，ASL20似乎参与了一个调控TE分化相关基因的VND7表达的正反馈环。
