Journal Article

Involvement of α-Amylase I-1 in Starch Degradation in Rice Chloroplasts

Satoru Asatsuma, Chihoko Sawada, Kimiko Itoh, Mitsutoshi Okito, Aya Kitajima and Toshiaki Mitsui

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 6, pages 858-869
Published in print June 2005 | ISSN: 0032-0781
Published online June 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci091
Involvement of α-Amylase I-1 in Starch Degradation in Rice Chloroplasts

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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To determine the role of α-amylase isoform I-1 in the degradation of starch in rice leaf chloroplasts, we generated a series of transgenic rice plants with suppressed expression or overexpression of α-amylase I-1. In the lines with suppressed expression of α-amylase I-1 at both the mRNA and protein levels, seed germination and seedling growth were markedly delayed in comparison with those in the wild-type plants. However, the growth retardation was overcome by supplementation of sugars. Interestingly, a significant increase of starch accumulation in the young leaf tissues was observed under a sugar-supplemented condition. In contrast, the starch content of leaves was reduced in the plants overexpressing α-amylase I-1. In immunocytochemical analysis with specific anti-α-amylase I-1 antiserum, immuno-gold particles deposited in the chloroplasts and extracellular space in young leaf cells. We further examined the expression and targeting of α-amylase I-1 fused with the green fluorescent protein in re-differentiated green cells, and showed that the fluorescence of the expressed fusion protein co-localized with the chlorophyll autofluorescence in the transgenic cells. In addition, mature protein species of α-amylase I-1 bearing an oligosaccharide side chain were detected in the isolated chloroplasts. Based on these results, we concluded that α-amylase I-1 targets the chloroplasts through the endoplasmic reticulum–Golgi system and plays a significant role in the starch degradation in rice leaves.

Keywords: α-Amylase; Chloroplast; Glycoprotein; Golgi complex; Oryza sativa L.; Starch; Transgenic plant; AU, arbitary unit; CaMV, cauliflower mosaic virus; Endo-H, endoglycosidase H; ER, endoplasmic reticulum; GFP, green fluorescent protein; PBS, phosphate-buffered saline; PSL, photo-stimulated luminescence; Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase; UGPase, UDPglucose pyrophosphorylase

Journal Article.  7798 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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