Over-expression of master regulators for cold tolerance can produce cold-tolerant leaves and photosynthetic apparatus, including tolerance to photoinhibition in winter. Over-expression of two endogenous cold-binding factor/drought responsive element binding (CBF/DREB)1-like genes in rape (B. napus) increased freezing tolerance and improved photochemical efficiency and photosynthetic capacity. These transgenics were less affected by photoinhibition induced by low temperatures and high insolation [99]. Similarly, over-expression of two CBF/DREB genes from Eucalyptus gunnii, a species that can withstand winter temperatures down to −18 °C, improved drought and freezing tolerance of a cold-sensitive Eucalyptus hybrid (E. urophylla × E. grandis) [136]. Tropical E. grandis × E. urophylla expressing a stress-inducible rd29a promoter-CBF2 transcription factor cassette demonstrated stable tolerance to −8 °C in a variety of locations through multiple years with no significant loss in productivity [130].
endogenous cold-binding factor/drought responsive element binding (CBF/DREB)1-like genes
two
CBF/DREB genes
two
Eucalyptus gunnii
withstand winter temperatures
down to −18 °C
°C
Tropical E. grandis × E. urophylla expressing a stress-inducible rd29a promoter-CBF2 transcription factor cassette
stable tolerance
−8 °C
°C