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MACHIDA Laboratory

How are upper and lower domains in leaves developed?

Leaves are important organs as a role of photosynthesis. Leaves of angiosperms exhibit remarkable diversity in terms of both shape and complexity. Nonetheless, the basic structure of each leaf generally develops along three axies and shape of leaves is symmetrical and flat. In addition leaves are developed along the adaxial (upper) - abaxial (lower) axis, resulting in composition of upper and lower cells. Palisade and Spongy tissues are developed in upper and lower domains, respectively.

Recent molecular and genetic works revealed that the small RNAs act an important role for the adaxial- abaxial axis determination of leaves. Small RNAs were found as regulators of post-transcriptional gene expression (PTGS) in both plants and animals in the late of 1980s. There might be common mechanisms for biogenesis of small RNAs in eucaryotes. Some factors involved in biogenesis of small RNAs are localized on the periphery of nucleoli. Although the levels of small RNAs are critical in each biological function, it is not yet known how the levels of small RNAs are regulated.

The ASYMMETRIC LEAVES1 (AS1) and ASYMMETRIC LEAVES2 (AS2) genes in Arabidopsis thaliana are involved in cell fate determination of three axies in leaves. We found that AS1 and AS2 proteins were colocalized as subnuclear bodies around the periphery of nucleoli (by T. Ishikawa in The Plant Cell, 2007), which we designated the AS2 bodies (see Figure and Movie). Our recent data suggested that AS1 and AS2 are taken part in regulation of the amounts of one of the small RNAs that act during upper and lower axis development in leaves of A. thaliana. We now would like to find a clue to know the regulation mechanisms of biogenesis of small RNAs by using Arabidopsis thaliana.

Professor Machida

Figure. Nucleolus is a structure in nucleus. Transcription of ribosomal RNA and construction of ribosomes are occurred in nucleoli

Movie.avimovie file
movie file
Fluorescent signals due to AS2-YFP fusion protein in young leaves of a transgenic plant are localized as subnuclear bodies around the periphery of nucleoli. Fluorescence due to YFP of the transgenic plant was monitored by confocal laser scanning microscopy. Bar = 3μm. Click the picture for movie.

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