title: Identification and characterization of a novel cassava (Manihot esculenta Crantz) clone with high free sugar content and novel starch.
abstract: This study reports the identification of a new class of cassava (Manihot esculenta Crantz) with a storage root showing unusual free sugar accumulation and novel starch. Twenty-seven clones high in free sugar were identified under cultivation in primitive rural community areas in the Amazon. Iodine test and glucose oxidase-peroxidase reagent strips were used, in the field, for identification of starch and glucose, respectively. Five out of these 27 clones of cassava were cultivated at EMBRAPA Genetic Resources and Biotechnology and used for biochemical characterization, starch synthesis enzyme activities and gene expression analysis. Carbohydrates were fractioned into free sugar, polymerized water-soluble and -insoluble alpha-polyglucan. Clones of series CAS36 accumulate over 100 times more free sugar (mainly glucose) than commercial varieties. Monosaccharide composition analysis revealed one clone with distinct water-soluble sugars not present in the commercial cultivar. Structure analysis of the water-soluble and -insoluble alpha-polyglucan revealed the presence of a glycogen-like starch in clone CAS36.1. This clone indicated disruption in the starch synthesis pathway for enzyme activities and protein blot analyses in ADPG-pyrophosphorylase and branching enzyme, and their corresponding protein. Gene expression analysis indicated the lack of transcript for the gene coding for branching enzyme, but not for the gene coding for the ADPG-pyrophosphorylase small subunit. In addition, the pattern of distribution of sugar and starch content showed to be related to tissue age in the storage root.
authors.affiliation: EMBRAPA Genetic Resources and Biotechnology, Brasilia, DF, Brazil, carvalho@cenargen.embrapa.br.
authors.forename: Luiz Joaquim Castelo Branco
authors.initials: LJ
authors.lastname: Carvalho
authors.forename: Claudia Regina Batista
authors.initials: CR
authors.lastname: de Souza
authors.forename: Julio César
authors.initials: JC
authors.lastname: de Mattos Cascardo
authors.forename: Carlos Bloch
authors.initials: CB
authors.lastname: Junior
authors.forename: Laura
authors.initials: L
authors.lastname: Campos
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics / Q000378:metabolism; D050260:Carbohydrate Metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D005947:Glucose / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase; D002365:Manihot / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D009005:Monosaccharides / Q000378:metabolism; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013213:Starch / Q000378:metabolism*; D013214:Starch Synthase / Q000235:genetics / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D009005:Monosaccharides; D012333:RNA, Messenger; D013395:Sucrose; D013213:Starch; D015061:1,4-alpha-Glucan Branching Enzyme; D013214:Starch Synthase; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase; D005947:Glucose