Analytical study on the importance and the mechanism of chloroplast photorelocation movement

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Importance of chloroplast avoidance response in plants.Using different classes of mutant, phot2 and chup1, defective in chloroplast avoidance movement, we show that these mutants are more susceptible to necrotic damage in high light than wild-type plants. We conclude that chloroplast avoidance movement actually reduces the amount of light absorption by chloroplasts, and might thus play an important role in the survival of plants under natural growth conditions.Function of phytochrome 3 in ferns.In some ferns, phototropism and chloroplast photorelocation are controlled by red light as well as blue light, but the photoreceptor had not been identified. We identify a function of phytochrome 3 (phy3), a chimera of phytochrome and phototropin, both for red light-induced phototropism and chloroplast photorelocation. Since phy3 greatly enhances the sensitivity to white light in orienting leaves and chloroplasts, this chimeric photoreceptor may have played a key role in the divergence and proli … More feration of fern species under low-light canopy conditions.CHUP1 function for organellar positioning and movement.CHUP1 encodes a protein containing multiple domains, such as an actin-binding domain and a proline-rich region. The fusion protein of CHUP1 and GFP expressed in leaf cells was targeted to the outer envelope of chloroplasts, suggesting CHUP1 localization in chloroplasts. CHUP1 was found to bind F-actin in vitro. CHUP1 is thus identified as a protein required for organellar positioning and movement in plant cells.Functional domain of PHOT2.The avoidance movement in Adiantum phot2 mutants could be restored by transient expression of non-mutant AcPHOT2 cDNA, indicating that the chloroplast avoidance movement in this fern is mediated by the Acphot2 protein. Further functional analyses of the Acphot2 protein were performed using this transient assay for chloroplast avoidance movement. The results obtained suggest that the LOV2, but not the LOV1, domain of Acphot2 is essential for avoidance movement. Less