Nishimura Rieko, Ohmori Masayuki, Fujita Hironori, Kawaguchi Masayoshi
Department of Life Science, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Japan.
Proc Natl Acad Sci U S A. 2002 Nov 12;99(23):15206-10. doi: 10.1073/pnas.222302699. Epub 2002 Oct 23.
The developmental program of nodulation is regulated systemically in leguminous host species. A mutant astray (Ljsym77) in Lotus japonicus has lost some sort of its ability to regulate this symtem, and shows enhanced and early nodulation. In the absence of rhizobia, this mutant exhibits characteristics associated with defects in light and gravity responses. These nonsymbiotic phenotypes of astray are very similar to those observed in photomorphogenic Arabidopsis mutant hy5. Based on this evidence, we predicted that astray might contain a mutation in the HY5 homologue of L. japonicus. The homologue, named LjBzf, encodes a basic leucine zipper protein in the C-terminal half that shows the highest level of identity with HY5 of all Arabidopsis proteins. It also encodes legume-characteristic combination of motifs, including a RING-finger motif and an acidic region in the N-terminal half. The astray phenotypes were cosegregated with LjBzf, and the failure to splice the intron was detected. Nonsymbiotic and symbiotic phenotypes of astray were complemented by introduction of CaMV35SLjBzf. It is noteworthy that although Arabidopsis hy5 showed an enhancement of lateral root initiation, Lotus astray showed an enhancement of nodule initiation but not of lateral root initiation. Legume-characteristic combination of motifs of ASTRAY may play specific roles in the regulation of nodule development.
豆科宿主植物中根瘤形成的发育程序受到系统调控。百脉根中的一个突变体astray（Ljsym77）丧失了某种调节该系统的能力，并表现出根瘤形成增强且提前。在没有根瘤菌的情况下，该突变体表现出与光反应和重力反应缺陷相关的特征。astray的这些非共生表型与光形态建成的拟南芥突变体hy5中观察到的表型非常相似。基于这些证据，我们预测astray可能在百脉根的HY5同源物中存在突变。该同源物名为LjBzf，在其C端编码一个碱性亮氨酸拉链蛋白，与所有拟南芥蛋白中的HY5具有最高水平的同一性。它还编码豆科植物特有的基序组合，包括在N端的一个环指基序和一个酸性区域。astray的表型与LjBzf共分离，并且检测到内含子剪接失败。通过导入CaMV35SLjBzf，astray的非共生和共生表型得到了互补。值得注意的是，虽然拟南芥hy5表现出侧根起始增强，但百脉根astray表现出根瘤起始增强，而侧根起始没有增强。ASTRAY的豆科植物特有的基序组合可能在根瘤发育调控中发挥特定作用。
