Ectopic expression of KNOTTED1-like homeobox protein induces expression of cytokinin biosynthesis genes in rice
Ectopic expression of KNOTTED1-like homeobox protein induces expression of cytokinin biosynthesis genes in rice
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DOI：
10.1104/pp.106.085811
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发表时间：
2006-09-01
期刊：
影响因子：
7.4
通讯作者：
Matsuoka, Makoto
中科院分区：
文献类型：
--
作者：
Sakamoto, Tomoaki;Sakakibara, Hitoshi;Matsuoka, Makoto
一些植物激素如赤霉素（GAs）和细胞分裂素（CKs）是KNOTTED 1-like homeobox（KNOX）蛋白的潜在靶标。为了提高我们对KNOX蛋白在植物发育中的功能的理解，我们鉴定了水稻（Oryza sativa）的腺苷磷酸异戊烯基转移酶（IPT）基因，该基因催化CK生物合成的限速步骤。分子生物学研究表明，水稻基因组中有8个IPT基因，OsIPT 1至OsIPT 8，包括一个假基因OsIPT 6。OsIPTs在转基因水稻中的过表达抑制了根的发育，促进了腋芽的生长，表明OsIPTs在体内具有功能。OsIPT过表达的表型类似于KNOX过量生产的转基因水稻，尽管OsIPT过表达的水稻不形成根或异位分生组织，这两者都在KNOX过量生产中观察到。两个OsIPT基因OsIPT 2和OsIPT 3的表达上调响应于KNOX蛋白功能的诱导，其动力学与双子叶植物中KNOX蛋白的靶基因GA 20-氧化酶基因的下调相似。然而，这两个OsIPT基因的表达没有以反馈方式调节。这些结果表明，OsIPT 2和OsIPT 3在水稻发育过程中具有独特的作用，这是由KNOX蛋白控制的，而不是在维持生物活性CK水平。基于这些发现，我们得出结论，KNOX蛋白通过诱导OsIPT 2和OsIPT 3的表达，同时减少GA的生物合成并增加CK的从头生物合成，并且由此产生的高CK和低GA条件是分生组织的形成和维持所必需的。
Some phytohormones such as gibberellins (GAs) and cytokinins (CKs) are potential targets of the KNOTTED1-like homeobox (KNOX) protein. To enhance our understanding of KNOX protein function in plant development, we identified rice (Oryza sativa) genes for adenosine phosphate isopentenyltransferase (IPT), which catalyzes the rate-limiting step of CK biosynthesis. Molecular and biochemical studies revealed that there are eight IPT genes, OsIPT1 to OsIPT8, in the rice genome, including a pseudogene, OsIPT6. Overexpression of OsIPTs in transgenic rice inhibited root development and promoted axillary bud growth, indicating that OsIPTs are functional in vivo. Phenotypes of OsIPT overexpressers resembled those of KNOX-overproducing transgenic rice, although OsIPT overexpressers did not form roots or ectopic meristems, both of which are observed in KNOX overproducers. Expression of two OsIPT genes, OsIPT2 and OsIPT3, was up-regulated in response to the induction of KNOX protein function with similar kinetics to those of down-regulation of GA 20-oxidase genes, target genes of KNOX proteins in dicots. However, expression of these two OsIPT genes was not regulated in a feedback manner. These results suggest that OsIPT2 and OsIPT3 have unique roles in the developmental process, which is controlled by KNOX proteins, rather than in the maintenance of bioactive CK levels in rice. On the basis of these findings, we concluded that KNOX protein simultaneously decreases GA biosynthesis and increases de novo CK biosynthesis through the induction of OsIPT2 and OsIPT3 expression, and the resulting high-CK and low-GA condition is required for formation and maintenance of the meristem.