Overexpression of Mannitol-1-Phosphate Dehydrogenase Increases Mannitol Accumulation and Adds Protection Against Chilling Injury in Petunia

Abstract

<jats:p><jats:italic>Petunia</jats:italic> ×<jats:italic>hybrida</jats:italic> (Hook) Vilm. cv. Mitchell was transformed with an <jats:italic>E. coli</jats:italic> gene encoding mannitol-1-phosphate dehydrogenase (<jats:italic>mtlD</jats:italic>). Four plant lines that grew on kanamycin and contained the <jats:italic>mtlD</jats:italic> transgene were identified. Two of these lines contained high levels of mannitol [high-mannitol lines M3 and M8; mean mannitol = 3.39 μmol·g<jats:sup>-1</jats:sup> dry weight (DW)] compared to nontransformed wild-type plants (0.86 μmol·g<jats:sup>-1</jats:sup> DW), while two lines had mannitol levels similar to wild-type plants (low-mannitol lines M2 and M9; mean mannitol = 1.05 μmol·g<jats:sup>-1</jats:sup> DW). Transgenic and control plants were subjected to chilling stress (3 ± 0.5 °C day/0 ± 0.5 °C night, 12-hour photoperiod and 75% relative humidity) to evaluate the role of mannitol in chilling tolerance. Based upon foliage symptoms and membrane leakage after a 3-week chilling treatment, the high-mannitol containing lines, M3 and M8, were more tolerant of chilling stress than the low-mannitol containing transgenic lines, M2 and M9, and wild-type. Under nonchilling conditions mannitol was the only carbohydrate that differed among transgenic lines, but all carbohydrates were present. When subjected to chilling stress, mannitol levels dropped by 75%, sucrose by 52%, and inositol by 54% in the low-mannitol lines (M2 and M9). In M3 and M8, the high-mannitol lines, mannitol levels decreased by 36%, sucrose by 25%, and inositol by 56%, respectively. Raffinose increased 2- to 3-fold in all lines following exposure to low-temperature chilling stress. In the higher mannitol lines only 0.04% to 0.06% of the total osmotic potential generated from all solutes could be attributed to mannitol, thus its action is more like that of an osmoprotectant rather than an osmoregulator. This study demonstrates that metabolic engineering of osmoprotectant synthesis pathways can be used to improve stress tolerance in horticultural crops.</jats:p>

Enhanced salt stress tolerance in transgenic potato plants (Solanum tuberosum L.) expressing a bacterial mtlD gene

“…However, these results also demonstrated that the amount of accumulated mannitol was too small to account for its effect as an osmolyte; therefore, the authors suggested that it might act as an oxygen free radical scavenger. Similar results have been reported for transgenic eggplants (Prabhavathi et al 2002) and petunia (Chiang et al 2005) that expressed the bacterial mtlD gene. Enhanced tolerance to salt stress has also been reported in trees such as loblolly pine (Tang et al 2005) and poplar (Hu et al 2005).…”

“…However, the mannitol content in individual lines was variable. Similar results have been reported for transgenic tobacco (Tarczynski et al 1993;Ruperez and Toledano 2003), Arabidopsis (Thomas et al 1995;Zhifang and Loescher 2003), petunia (Chiang et al 2005), loblolly pine (Tang et al 2005), and eggplant (Prabhavathi and Rajam 2007). Variations in the mannitol content may be due to copy number and to the positional effects of the transgene that may result in differential expression of the transgene in different lines (Hobbs et al 1990;Celebi-Toprak et al 2005;Tang et al 2005;Waditee et al 2007).…”

“…Expression of the mtlD gene in eggplant resulted in an increased tolerance to osmotic stress that was induced by salt, drought, and chilling stresses (Prabhavathi et al 2002). Similar results have been achieved by the genetic transformations of petunia (Chiang et al 2005), loblolly pine (Tang et al 2005), poplar (Hu et al 2005), and rice (Huizhong et al 2000) with mtlD gene.…”

Mannitol Utilisation is Required for Protection of Staphylococcus aureus from Human Skin Antimicrobial Fatty Acids

“…The expression of a bacterial mtlD in Saccharomyces cerevisiae was sufficient to generate mannitol which was proposed to act as an osmolyte and was sufficient to rescue the phenotypes of a glycerol deficient mutant, producing an increased resistance to high salt and H 2 O 2 [45]. Mtl is also proposed to function as an osmoprotectant in cells of petunia as well as improving cold tolerance [46].…”

Draft Genome Sequence of Halomonas elongata Strain K4, an Endophytic Growth-Promoting Bacterium Enhancing Salinity Tolerance In Planta

“…An additional gene ectD coding for ectoine hydroxylase (EC: 1/14/11) is present, and this enzyme converts ectoine to hydroxyectoine (15). Furthermore, the genome encoded other osmoprotectant-related enzymes such as trehalose phosphatase (EC:3.1.3.12) (16) and mannitol-1-phosphate 5-dehydrogenase (EC:1.1.1.17) (17), suggesting a possible role for this endophyte in enhancing salinity tolerance in plants.…”