Functional differentiation of the sugar beet root system as indicator of developmental phase change

Abstract

Developmental phase transitions in the plant root system have not been well characterized. In this study we compared the dynamics of sucrose accumulation with changes in gene expression analyzed with cDNA-amplified fragment length polymorphism (AFLP) in the developing tap root of sugar beet (Beta vulgaris, L.) during the first 9 weeks after emergence (WAE). Although differences between lines were evident as soon as 9 WAE, sucrose showed a marked increase in the rate of accumulation between 4 and 6 WAE and a remarkable shift in gene expression was observed between 5 and 6 WAE. These changes were evident in two unrelated genetic backgrounds and suggest that physiological and gene expression changes represent a functional differentiation of the tap root. These changes were considered as indicators of a developmental change in the sugar beet root system. To identify genes and metabolic pathways involved in this developmental shift, a root cDNA library was hybridized with probes enriched for 3- and 7-WAE transcripts and differentially expressed transcripts were analyzed by cDNA microarray. Several genes involved in the regulation of tissue development were found to be differentially regulated. Genes involved in protein metabolism, disease-related and secretory system were upregulated before the functional differentiation transition, while genes under hormonal control were upregulated after the functional differentiation transition. This developmental phase change of the root system is important to understand plant developmental regulation at the whole-plant level and will likely be useful as early selection parameter in breeding programs.

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

“…Sugar beet is stated to be fully active in a quite early stage [23]. Parsnip has to our knowledge not been investigated in this aspect.…”

Transcriptomic profiling of taproot growth and sucrose accumulation in sugar beet (Beta vulgaris L.) at different developmental stages

“…Previously, studies using cDNA amplified fragment length polymorphism (AFLP), ESTs [2, 3] and microarray analyses [4, 5] have been performed to understand the basis of taproot growth and sucrose accumulation at both morphological [6, 7] and physiological levels in sugar beet [8]. During the early development of taproot [5], expressions of genes involved in cell division, as well as those in water and non-electrolyte small molecule transport system, were preferentially expressed.…”

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

“…The distinct shape of a sugar beet and its correlation to sugar storage capability has been studied in the past (De Vries, 1879; Artschwager, 1926; Heinisch, 1960), and researchers had to rely on large numbers of plants and several harvests to get information on average beet development (Ulrich, 1952; Trebbi and Mcgrath, 2009). While different shapes at harvest were extensively characterized and used as criteria in breeding selection, the development of individual beets and its role in performance and yield formation could not be investigated.…”

“…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.…”