Morphological and molecular characterization of a spontaneously tuberizing potato mutant: an insight into the regulatory mechanisms of tuber induction

Lukas Fischer,Jean-Francois Hausman,Zdenek Opatrny,Helena Lipavska

doi:10.1186/1471-2229-8-117

Abstract

BackgroundTuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation. In the present work, we studied the regulatory mechanisms and the role of different morphogenetic factors in a newly isolated potato mutant, which exhibited spontaneous tuberization (ST). The ST mutant was characterized in detail at morphological, physiological and biochemical levels.ResultsTuberization of the ST mutant grown in the soil was photoperiod-insensitive; predominantly sessile tubers formed directly from axillary buds even under continuous light. Single-node cuttings of the ST mutant cultured in vitro frequently formed tubers or basal tuber-like swellings instead of normal shoots under conditions routinely used for shoot propagation. The tuberization response of ST cuttings under light was dependent on sucrose, the concentration of which had to exceed certain threshold that inversely correlated with irradiance. Gibberellic acid prevented tuberization of ST cuttings, but failed to restore normal shoot phenotype and caused severe malformations. Carbohydrate analysis showed increased levels of both soluble sugars and starch in ST plants, with altered carbohydrate partitioning and metabolism. Comparative proteomic analysis revealed only a few differences between ST- and wild-type plants, primary amongst which seemed to be the absence of an isoform of manganese-stabilizing protein, a key subunit of photosystem II.ConclusionST mutant exhibits complex developmental and phenotypic modifications, with features that are typical for plants strongly induced to tuberize. These changes are likely to be related to altered regulation of photosynthesis and carbohydrate metabolism rather than impaired transduction of inhibitory gibberellin or photoperiod-based signals. The effect of gibberellins on tuberization of ST mutant suggests that gibberellins inhibit tuberization downstream of the inductive effects of sucrose and other positive factors.

Highlights

Tuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation
We have identified a single T-DNA insertion in the spontaneous tuberization (ST) mutant genome by Southern hybridization using probes prepared from both ends of the T-DNA
The absence of manganese stabilizing protein (MSP) isoform in the ST mutant suggests that the phenotypic changes may have resulted from altered photosynthetic machinery, which is of high general interest

Summary

Introduction

Tuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation. Tuber induction in potato (Solanum tuberosum L.) is a complex, multilevel process, which integrates environmental and internal signals to ensure optimal life strategy during the growing season (reviewed in [34,37]). Photoperiodic signal is integrated with other environmental factors, such as nitrogen availability, temperature and light intensity, as well as with the overall metabolic status of the plant, so that the plants can tuberize even under long-day photoperiods (reviewed in [16]). Plants exposed to conditions that favor tuberization display significant metabolic and growth changes in both above- and underground organs. Active storage of carbohydrates in tubers leads to reduced vegetative growth, flowering and fruiting (reviewed in [7])

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