PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Effects of over-expression of BNCBF transcription factors on photosynthetic cold stress tolerance of Brassica napus. Leonid Savitch^*,1, Ghislaine Allard¹, Nick Tinker¹, Laurian Robert¹, Norman Huner², Motoaki Seki³, Kazuo Shinozaki³, Jas Singh¹, ¹ Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, Ottawa, Ontario, Canada² Department of Biology, The University of Western Ontario, London, Ontario, Canada³ Biological Resources Division, Japan International Research Centre for Agricultural Sciences, Tsukuba, Ibaraki, Japan

ABSTRACT- Two CBF/Dreb transcription factors (BNCBF5, 17) were isolated from winter Brassica napus cv Jet Neuf. and reintroduced into the spring Brassica napus cv. Westar. Transgenic plants overexpressing BNCBF 5 and 17 constitutively accumulate COR gene mRNAs and showed improved frost tolerance over the wild type in the absence of cold acclimation based on both whole seedling freezing and leaf electrolyte leakage. Plants overexpressing (OE) BNCBF17 exhibited a higher level of constitutive frost tolerance than those overexpressing BNCBF5 (-12^oC vs -8^oC respectively). Furthermore BNCBF5 and 17 OE plants were able to acclimate and develop freezing tolerance more rapidly than the wild type. This was associated with BNCBF5 and 17 OE plants having respectively 47 and 57% higher specific leaf weight (SLW), increased total pigment pool size and increased capacity for CO2 assimilation and linear electron transport compared to the wild type plants when grown under control conditions. Moreover, increased resistance to low temperature induced photoinhibition observed in BNCBF5 and 17 OE plants in the absence of cold acclimation was, in part, associated with increased photochemical efficiency and photosynthetic capacity and not with differential ROS scavenging capacity and involvement of xanthophyll cycle pigment in heat dissipation. Effects of cold stress as well as BNCBF5 and 17 OE on gene expression profiles were monitored using a 2K Brassica cDNA microarray in conjunction with Northern blot analyses. In addition, the effect of BNCBF17 OE on gene expression was also monitored using the 8K RAFL cDNA array. Interestingly, the majority of genes observed to be moderately upregulated using both arrays encode chloroplast proteins. Increased accumulations of mRNA encoding GLK2 (a myb factor implicated in chloroplast development), ROC4 and LON protease were confirmed by Northern analyses. In addition, upregulation of genes encoding beta-amylase and triose-P/Pi translocator suggests that similar alterations in photosynthetic carbon metabolism might be expected in cold treated wild type as well as BNCBF5 and 17 OE plants.

KEY WORDS: photosynthetic cold stress tolerance, CBF/Dreb transcription factors, freezing tolerance, Brassica napus