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Plant and Cell Physiology Advance Access originally published online on July 20, 2009
Plant and Cell Physiology 2009 50(9):1617-1626; doi:10.1093/pcp/pcp104
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Amyloplast Division Progresses Simultaneously at Multiple Sites in the Endosperm of Rice

Min-Soo Yun and Yasushi Kawagoe*

Division of Plant Sciences, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, 305-8602 Japan

*Corresponding author: E-mail, kawagoe{at}nias.affrc.go.jp; Fax, +81-29-838-7417.


  Abstract

The amyloplast, a form of differentiated plastid, proliferates in sink tissues, where it synthesizes and stores starch granules. Little is known about the molecular mechanism for amyloplast division and development. The rice (Oryza sativa) endosperm provides an excellent model system for studying molecular mechanisms involved in amyloplast division and starch synthesis. We compared amyloplast division processes in the endosperm of wild type and a mutant of ARC5, a member of the dynamin superfamily. Plant growth and fertility of arc5 were not significantly different from the wild type. Unlike binary fission of chloroplast in the leaf, small amyloplasts in the endosperm of wild type divide simultaneously at multiple sites, generating a beads-on-a-string structure. In addition, large amyloplasts divide by budding-type division, giving rise to small amyloplasts attached to their surfaces. ARC5 and FtsZ2-1 fused to fluorescent proteins were targeted to the constriction sites in dividing amyloplasts. Both the loss of function of ARC5 and overexpression of ARC5 fusion proteins in the endosperm did not produce spherical amyloplasts with increased diameter, but produced either fused amyloplasts with thick connections or pleomorphic types, suggesting that proper stoichiometry between ARC5 and other components in the amyloplast division machinery is necessary for the completion of the late stage of amyloplast division. The size distribution of starch granules purified from arc5 was shifted to small and the starch gelatinization peak temperature was significantly higher than for wild-type starch, suggesting that amyloplast division processes have a significant effect on starch synthesis.

Keywords: Amyloplast division - ARC5 - Endosperm - FtsZ - Rice - Starch granule

Abbreviations: DSC, differential scanning calorimetry; GFP, green fluorescent protein; IEM, inner envelope membrane; IPTG, isopropyl β-D-thiogalactoside; OEM, outer envelope membrane; ORF, open reading frame; PBS, phosphate-buffered saline; PVDF, polyvinylidene fluoride; RFP, red fluorescent protein.

(Received June 9, 2009; Accepted July 9, 2009)
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