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Incorporation of two trehalose biosynthetic genes in banana increases trehalose levels and protects the photosynthetic apparatus from salt-stress damage

Summary There are no reports on the possible protective role of trehalose in tropical monocot plants such as banana, when exposed to salt stress. In the present work, banana plants (Musa acuminata ‘Grand Nain’) were transformed with a fusion of two genes from Saccharomyces cerevisiae involved in the biosynthetic pathway of trehalose [trehalose-6-phosphate synthase (tps); and trehalose-6-phosphate phosphatase (tpp)] under the control of the Arabidopsis rd29A drought-stress inducible promoter. Transformed (rd29A::tps-tpp; TF) and wild-type (WT) plants were subjected to three different concentrations of NaCl (100, 200, or 300 mM) for 9 d. The trehalose concentration in the leaves of WT plants was approx. 3.5 µg g−1 fresh weight (FW) when not exposed to salinity, and increased only slightly (to 4.0 µg g−1 FW) when exposed to 100 or 200 mM NaCl. In TF plants, however, the trehalose concentration was approx. 4.0 µg g−1 FW when not exposed to salinity, but increased with salinity, reaching values of ≥ 8.0 µg g−1 FW, when exposed to 300 mM NaCl. WT plants were severely affected when exposed to salinity, reducing their photosynthetic rates, (from 6.0 to 1.5 µmol CO2 m−2 s−1 at 0 and 200 mM NaCl, respectively, with an extensively damaged photosystem II [i.e., the ratio of maximum variable fluorescence to maximum fluorescence (Fv/Fm) decreased from 0.85 to 0.58, at 0 and 300 mM NaCl, respectively]. On the other hand, TF plants were able to withstand salt stress and showed a lower reduction in photosynthetic rate (from 7.0 to 4.0 µmol CO2 m−2 s−1, at 0 and 200 mM NaCl, respectively) and a lessaffected photosystem II (i.e., the Fv/Fm ratio only decreased from 0.85 to 0.75, at 0 and 300 mM NaCl, respectively). The superior ability of TF plants to protect their photosynthetic performance when exposed to salinity was confirmed by measuring additional chlorophyll fluorescence (CF) parameters. These results provide the first evidence that trehalose can protect against abiotic stress in a tropical monocot plant such as banana.