Transcript profiles at different growth stages and tap-root zones identify correlated developmental and metabolic pathways of sugar beet

Abstract

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 degrees 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 degrees Cd. Cluster analysis identified 543 transcripts with reproducible preferential expression between 1300-1400 degrees 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.

Starch biosynthetic genes and enzymes are expressed and active in the absence of starch accumulation in sugar beet tap-root

“…On tissue sections of the sampled sugar beet roots, 3–5 secondary cambium rings could be seen (Additional file 2). A mature sugar beet root consists of about 12 secondary cambium rings, where the first 8 cambium rings develop during the first 8 weeks [20]. Our results verified that the plants sampled were an appropriate material for this study.…”

“…For example, mutants or silencing of these two genes as well as transgenic silencing studies of Arabidopsis and pea display low starch content, but not a complete loss of starch accumulation [31-33]. Similarly as found in this study, expression of some of the genes encoding for these key enzymes can be found as expressed in sugar beet when assessing supplementary information of Bellin et al [20]. Generally, support functions for starch synthesis such as genes encoding transporters for hexose phosphates and energy in the form of ATP were found to be less expressed in sugar beet than in parsnip tap-root although a complete lack of expression only was seen for a couple of transcripts.…”

Genetic approaches to sustainable pest management in sugar beet (Beta vulgaris)

“…ESTs (21 321) representing 13 618 genes have been cloned from sugar beet (3 February 2005 release, http://compbio. dfci.harvard.edu/tgi/cgi-bin/tgi/gimain.pl?gudb=beet; Herwig et al, 2002;Bellin et al, 2007). There are 26 870 ESTs deposited in the GenBank (accessed on 13 November 2007), of which about 20% are estimated to represent defence, signal transduction and secondary product synthetic genes.…”

Belowground plant development measured with magnetic resonance imaging (MRI): exploiting the potential for non-invasive trait quantification using sugar beet as a proxy

“…No clear correlation with sugar yield was found for simple traits such as number and width of rings or parenchyma cell size at harvest (Draycott, 2006), even though several studies argued that, with shorter distances between phloem and storage tissues, a higher sucrose content should be achievable (Milford, 1973; Wyse, 1979; Doney et al, 1981). Also cDNA cloning of extracellular and vacuolar sucrose cleaving enzymes revealed a change in the mechanisms of the functional unloading pathways during the first weeks of beet development, and transcript profiles revealed developmental and metabolic changes at similar or later age (Godt and Roitsch, 2006; Bellin et al, 2007; Trebbi and Mcgrath, 2009). However, it could not be correlated with the development of structural traits such as tissue volume or growth rates.…”