Water Stress in Beta vulgaris: Osmotic Adjustment Response and Gene Expression Analysis in ssp. vulgaris and maritima

Beta vulgaris genus comprises wild and cultivated subspecies. The “maritima” subspecies is formed by wild or weedy accessions, well adapted to low-water potential environments; it was previously shown that B. vulgaris ssp. maritima has mechanisms of osmotic adjustment more effective than the cultivated B. vulgaris ssp. vulgaris. The response to a progressive lowering of soil potential was compared in two Beta accessions, a cultivated and a wild one. Throughout the 4-months experiment under rain shelters, osmotic potential and relative water content were measured and total RNA was extracted to test the expression of six target genes known in sugar beet or in other plants to be modulated by water shortage. The mild occurrence of drought was paralleled by slow increase in transcription for sucrose synthase 1 and choline monoxygenase, in a way that was in some cases accession-dependent, e.g. the gene for choline monoxygenase was found to be up-regulated at the later stages of growth in stressed plants compared to control ones, and showed a higher constitutive transcription in sea beet compared to sugar beet. Transcription factor DREB2A also was slowly induced during the growth season and upon onset of water shortage, and this induction was stronger in sea beet than in sugar beet. In control plants, the transcription of all genes tested except DREB2A were significantly higher in maritima accession compared to vulgaris one.