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Green Roots

The regulatory mechanism of chloroplast biogenesis in roots

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Graduate School of Arts and Sciences / College of Arts and Sciences
2012/03/15

Cells in higher plants develop a variety of plastids, organelles that fulfill functions specific to the purpose of that cell. For example, green cells in leaves contain chloroplasts, photosynthetic plastids that harvest energy from sunlight and give leaves their color.

Induced chloroplast differentiation results in green roots
In roots (GLK2ox and GLK1ox) that over-express the transcription factor GLK involved in chloroplast differentiation, chloroplast differentiation is induced and the roots take on a striking green color. The red color in the above image marking the chlorophyll accumulated in chloroplasts indicates the degree of greening.

In contrast, root cells growing underground usually contain non-photosynthetic plastids, for example for storing starch, and depend on leaves as their energy source. Although it is known that differentiation of plastids is tightly coordinated with plant development, the coordination mechanism still remains unclear.

An international research team led by Associate Professor Tatsuru Masuda and Assistant Professor Koichi Kobayashi at the Graduate School of Arts and Sciences Department of Multi-Disciplinary Sciences has shown that Arabidopsis thaliana roots demonstrate accelerated chlorophyll accumulation and chloroplast development when they are detached from shoots.

This phenomenon is repressed by exogenous treatment with the plant hormone auxin, showing that auxin from shoots represses chloroplast biogenesis in roots. On the contrary, another plant hormone, cytokinin, functions positively on chlorophyll biosynthesis in roots. Regulation by auxin/cytokinin is dependent on two types of transcription factors, HY5 and GLKs; the former is an essential factor for the expression of photosynthetic genes in roots and the latter, while not essential, is a strong activator of such genes.

This finding will enable manipulation of root chloroplast development and maximize root photosynthetic activity, which in the future could lead to an improvement of the carbon economy of cultivated crops.

Press release (Japanese)

Paper

Koichi Kobayashi, Shinsuke Baba, Takeshi Obayashi, Mayuko Sato, Kiminori Toyooka, Mika Keranen, Eva-Mari Aro, Hidehiro Fukaki, Hiroyuki Ohta, Keiko Sugimoto, and Tatsuru Masuda,
“Regulation of Root Greening by Light and Auxin/Cytokinin Signaling in Arabidopsis,”
The Plant Cell Online Edition
Article link

Links

Graduate School of Arts and Sciences

Tatsuru Masuda Laboratory

Wada and Kobayashi Laboratory

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