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Regulation of starch synthesis in cassava

Baguma, Yona (2004). Regulation of starch synthesis in cassava. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae. Agraria, 1401-6249 ; 478
ISBN 91-576-6766-7
[Doctoral thesis]

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Cassava (Manihot esculenta Crantz) is a root crop, one of the world’s most important but under-exploited staple food crops and source of income. It is a high starch producer with levels between 73.7 and 84.9% of its total storage root dry weight. Increasingly, there is a need for diverse novel starches for both food and non-food applications. In response, sbeII encoding starch branching enzyme II was cloned. The relationship between spatial-temporal expression patterns of starch synthesis genes and the plasticity of the storage root development states was examined. To gain further insight into the transcriptional activity of sbe, diurnal transcript abundances, sugar and hormone signaling were studied. Results showed that the transcriptional activity of sbe increased with the developmental states of the storage root. Analysis of sbe diurnal transcript patterns identified the existence of an endogenous semidian oscillator (12 h) in the storage root cells but its nature and function remains unknown. To elucidate the relationship between sbe expression and sugar status; a combination of biochemical, genomic, histological and therapeutic approaches were used. In these analyses, sucrose was identified as the main signal that mediates transcriptional induction of sbe. Other identified effectors were abscisic acid (ABA), glucose, glucose-1-phosphate (G-1-P) and turanose. Repeated experimentation located the semidian oscillator upstream of G-1-P/G-6-P but downstream of glucose at the level of hexokinase. The discovery that sbe expression is not induced by mannose, mannitol, 3-O-methyl- glucose and palatinose, but turanose, uncovered the existence of a sucrose transporter (SUT) and/or sensor. Notably, the induced sbe expression profile and level, and the biochemical properties of sucrose and turanose suggested that the SUT might as well as serve a sensor, although the existence of an independent extracellular sensor was not precluded. It was also shown that sucrose and ABA singly or in combination mediate sbe expression, and ABA by itself or with sucrose decouples the endogenous semidian oscillator via a bypass mechanism. Furthermore, it was revealed that either sucrose or ABA is not sufficient to promote maximal sbe expression, but the dual additive interactive effect is essential. The study also revealed the importance of protein phosphatases, protein kinases and first evidence for plastid de novo protein synthesis in the regulation of sbe expression. Okadaic acid, which preferentially inhibits type 1 and 2A protein phosphatases, PP1 and PP2A, respectively, abolished sbe expression, in the presence or absence of other effectors, i.e., sucrose, glucose, G-1-P, turanose and ABA. Conversely, cantharidin, a potent inhibitor of PP2A, did not, suggesting that sugar and ABA signaling pathways converge at the PP1 level downstream of the sugar signaling pathway. Chloramphenicol, which specifically inhibits plastid de novo protein synthesis, with or without sucrose, blocked sbe expression but cycloheximide, a cytosolic de novo protein synthesis inhibitor, did not, suggesting a role of plastid de novo protein synthesis in the regulation of sbe. The emerging implications from this study have been summarised into a working regulatory model for sbe expression. In summary, this work has established that sbe transcriptional activity depends on the plasticity of the storage root growth and development states, rhythmicity of an endogenous semidian oscillator, interactive effects of sucrose and ABA signaling pathways, plastid de novo protein synthesis, and dephosphorylation events.

Authors/Creators:Baguma, Yona
Title:Regulation of starch synthesis in cassava
Series Name/Journal:Acta Universitatis Agriculturae Sueciae. Agraria
Year of publishing :September 2004
Number of Pages:44
ALLI. Yona Baguma, Chuanxin Sun, Staffan Ahlandsberg, Joel Mutisya, Sara Palmqvist, Patrick R.Rubaihayo, Michael J. Magambo, Thomas G. Egwang, Håkan Larsson,Christer Jansson. 2003. Plant Science 164, (4): 833-839 II. Yona Baguma, Chuanxin Sun, Mats Borén, Helena Olsson, Sara Palmqvist, Joel Mutisya, Patrick R. Rubaihayo, Christer Jansson. 2004. Sugar-mediated semidian oscillation of starch synthesis genes in the cassava storage root. PNAS. Submitted III. Yona Baguma, Chuanxin Sun, Mats Borén, Joel Mutisya, Helena Olsson, Sara Palmqvist, Linley Chiwona-Karltun, Patrick R. Rubaihayo, Christer Jansson. 2004. Profiling starch accumulation in the storage roots of cassava. Science. Submitted IV. Yona Baguma, Chuanxin Sun, Joel Mutisya, Patrick R. Rubaihayo, Christer Jansson. 2004. Evidence for nucleo-plastid signaling during regulation of starch synthesis genes in the cassava storage root. Manuscript
Place of Publication:Uppsala
ISBN for printed version:91-576-6766-7
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:F Plant production > F30 Plant genetics and breeding
F Plant production > F62 Plant physiology - Growth and development
Subjects:Not in use, please see Agris categories
Agrovoc terms:cassava, amylopectin, amylose, starch crops, transcription, biosynthesis, sucrose, aba
Keywords:ADPG, alternative splicing, amylopectin, amylose, cassava, plastid signal
Permanent URL:
ID Code:614
Department:(NL, NJ) > Dept. of Plant Biology and Forest Genetics (until 131231)
Deposited By: Yona Baguma
Deposited On:08 Sep 2004 00:00
Metadata Last Modified:02 Dec 2014 10:06

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