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Transgenic Sugar Beet Expressing a Bacterial Mannitol-1-Phosphate Dehydrogenase (mtlD) Gene Shows Enhanced Resistance to Fungal Pathogens

Goudarzi, Azadeh, Jafari, Morad, Safaie, Naser, Mohammad Jafari, Setare
Sugar tech 2016 v.18 no.2 pp. 192-203
Alternaria alternata, Botrytis cinerea, Cercospora beticola, Escherichia coli, Southern blotting, bioassays, biotic stress, cold treatment, disease severity, drought, fungi, gene expression, high performance liquid chromatography, leaves, mannitol, pathogens, plant response, sugar beet, temperature, transgenes, transgenic plants
The E. coli mtlD gene encoding mannitol-1-phosphate dehydrogenase has been shown to be involved in the plant response to abiotic stresses such as salinity, drought and chilling. Nevertheless, in this study transgenic sugar beet lines containing the mtlD gene under control of a stress-inducible rd29A promoter were evaluated for their potential of resistance against three fungi including Alternaria alternata, Botrytis cinerea and Cercospora beticola. Southern blot analysis revealed the low copy number (1-3 copies) integration of the transgene in the transgenic lines. Expression profiling by semi-quantitative-RT-PCR analysis showed different levels of cold-inducible expression of mtlD in independent T₁ transformants. Mannitol content quantified by HPLC analysis ranged from 1.8 to 3.7 µmol g⁻¹ dry weight in different transgenic lines. Detached leaf bioassay showed that lower transgene expression levels in the transgenic line mt-LS4-32 under non-stressed conditions reduced the disease severity (DS) of A. alternata and B. cinerea by 49 to 87 %, respectively. At the whole-plant level, under non-stressed conditions, the transgenic line showed better performance to A. alternata with a delay of fungal symptom appearance. Following exposure to low temperature (4 °C), the transgenic line showed no fungal infection after 14 days of inoculation. Transgenic lines inoculated with C. beticola significantly (P < 0.001) showed higher resistance than the non-transformed control plants. DS in transgenic lines expressing mtlD gene was zero and 0.05 % compared to 25 % for the control. These results indicate that the mtlD gene can be used as a target to improve plant tolerance to both abiotic and biotic stresses.