Abstract
In potato plants, the phloem-mobile miR172 is involved in the sugar-dependent transmission of flower and tuber inducing signal transduction pathways and a clear link between solute transport and the induction of flowering and tuberization was demonstrated. The sucrose transporter StSUT4 seems to play an important role in the photoperiod-dependent triggering of both developmental processes, flowering and tuberization, and the phenotype of StSUT4-inhibited potato plants is reminiscent to miR172 overexpressing plants. The first aim of this study was the determination of the level of miR172 in sink and source leaves of StSUT4-silenced as well as StSUT4-overexpressing plants in comparison to Solanum tuberosum ssp. Andigena wild type plants. The second aim was to investigate the effect of sugars on the level of miRNA172 in whole cut leaves, as well as in whole in vitro plantlets that were supplemented with exogenous sugars. Experiments clearly show a sucrose-dependent induction of the level of mature miR172 in short time as well as long time experiments. A sucrose-dependent accumulation of miR172 was also measured in mature leaves of StSUT4-silenced plants where sucrose export is delayed and sucrose accumulates at the end of the light period.
Highlights
Sugar accumulation and starch biosynthesis in mature leaves follow day time dependent oscillations
The level of miR172 was significantly up-regulated in two independent sets of StSUT4 silenced plants: both StSUT4-RNAi plants from Solanum tuberosum ssp. tuberosum Désirée (Figure S1) as well as from Solanum tuberosum ssp
The results of our study demonstrate considerably higher level of miR172 in several transformant lines with reduced levels of StSUT4 expression compared to wild type plants
Summary
Sugar accumulation and starch biosynthesis in mature leaves follow day time dependent oscillations. Whereas the accumulation of transitory starch in leaves is strongly light-dark-dependent since the rate-limiting enzyme in starch biosynthesis, the ADPglucose pyrophosphorylase (AGPase) is regulated by light, the accumulation of soluble sugars in mature leaves oscillates during the day with maximum levels in the middle of the light period [1]. In accordance with this sugar accumulation the transcript amount of sucrose transporters follow a circadian rhythm and continue oscillation even under constant light conditions [1]. Potato plants with down-regulated StSUT4expression are early flowering and develop tubers even under non-inductive long day (LD)
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