Plant Physiology Preview
Published on February 7, 2008; 10.1104/pp.107.110304
OPEN ACCESS ARTICLE
Received October 2, 2007
Accepted January 30, 2008
Characteristic and expression analysis of a metallothionein gene, OsMT2b, down-regulated by cytokinin suggest functions in root development and seed embryo germination of rice (Oryza sativa L.)
Jing Yuan , Dan Chen , Yujun Ren , Xuelian Zhang , and Jie Zhao *
College of Life Sciences, Wuhan University, Wuhan 430072, China
* Corresponding author; email: jzhao{at}whu.edu.cn.
Metallothioneins (MTs) are low molecular mass and cysteine-rich metal-binding proteins known to be mainly involved in maintaining metal homeostasis and stress responses. But, their functions in higher plant development are scarcely studied. Here, we characterized OsMT2b (Oryza sativa Metallothionein 2b) molecularly and found that its expression was down-regulated by cytokinins. OsMT2b was preferentially expressed in rice immature panicles, scutellum of germinating embryos and primordium of lateral roots. In contrast with wild-type plants, OsMT2b-RNAi transgenic plants had serious handicap in plant growth and root formation, whereas OsMT2b-overexpressing transformants were dwarfed and presented more adventitious roots and big lateral roots. The increased cytokinin level in RNAi plants and decreased cytokinin level in overexpressing plants were confirmed by HPLC quantitative analysis in the roots of wild-type and transgenic plants. In RNAi plants, localization of isopentenyladenosine (iPA), a kind of endogenous cytokinin, in roots and germinating embryos expanded to the whole tissues, while in overexpressing plants, the iPA signals were very faint in the vascular tissues of roots and scutellum cells of germinating embryos. In vitro culture of embryos could largely resume the reduced germination frequency in RNAi plants but had no obvious change in overexpressing plants. Taken together, these results indicate a possible feedback regulation mechanism of OsMT2b to the level of endogenous cytokinins which is involved in root development and seed embryo germination of rice.
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