RESEARCH PAPER |
Transcript profiles at different growth stages and tap-root zones identify correlated developmental and metabolic pathways of sugar beet
1Max-Planck-Institute for Plant Breeding Research, Department of Plant Breeding and Yield Physiology, Carl-von-Linné Weg 10, D-50827 Köln, Germany
2KWS SAAT AG, Grimsehlstrasse 31, D-37555 Einbeck, Germany
3Institute of Genome Research, University of Bielefeld, D-33594 Bielefeld, Germany
4Fondazione Parco Tecnologico Padano, Via Albert Einstein c/o Polo Universitario, Cascina Codazza, I-26900 Lodi (Lo), Italy
5GSF – National Research Center for Environment and Health, Institute for Radiation Protection, Ingolstädter Landstrasse 1, D-85764 Neuherberg, Germany
* To whom correspondence should be addressed. E-mail: katharina.schneider{at}gsf.de
Field-grown sugar beets were analysed for morphological characters, sucrose content, and reproducible transcript profiles by macroarray analyses with 11 520 unique sugar-beet cDNA targets in two different years. Seasonal differences were partly compensated by expressing sampling dates as thermal time. During early beet development the number of cambial rings, root length, and sucrose concentration had already achieved >40% of their final values. Sucrose levels rose from 10% to 17% over the thermal time of 1300–1400 °Cd with only small changes later when lower concentrations were restricted to the exterior zone at the minimum of the spatial sucrose gradient through the beet. The number of leaves and root diameter followed the same temporal growth pattern, but mass increased until beet maturity at around 2000 °Cd. Cluster analysis identified 543 transcripts with reproducible preferential expression between 1300–1400 °Cd, and 170 showing the highest transcript levels later. In maturing beets, 373 transcripts were over-represented in the inner zone and 148 in the outer zone. During early development, genes involved in cytoskeletal reorganization and transport processes showed the highest transcript levels. Cell wall biogenesis-, defence-, stress-, and degradation-related transcripts were identified in all samples, and associated with pathogen attack during late development and in the outer zone. Candidates with potential roles in carbohydrate metabolism appeared to serve anaplerotic functions by converting excess intermediates to sucrose production. Transcripts preferentially occurring in sucrose-accumulating young beet cells and newly generated peripheral cells of mature beets are discussed as potential breeding targets to improve sink strength and growth.
Key words: Candidate genes, macroarray analysis, sucrose accumulation, sugar beet, tap root formation
Received 4 May 2006; Revised 24 October 2006 Accepted 25 October 2006