Abstract
We found, by the T-DNA activation-tagging method, that the Arabidopsis AtFIB5 gene may be involved in enhancing freezing tolerance. Two transcripts (FIB273 and FIB259), which are generated by pre-mRNA alternative splicing of the AtFIB5, are presumed to encode the proteins composed of 273 and 259 amino acids, respectively. To elucidate the function of these transcripts, we have studied involvement of the AtFIB5 gene in freezing tolerance with FIB5-overexpressing and -knockout plants. FIB5-knockout (fib5) plants exhibited a dwarf phenotype and a remarkable decline in freezing tolerance. These abnormalities were complemented by the introduction of cDNA of FIB273 into fib5 plants, while they were still observed in the FIB259-introduced plants. Meanwhile, FIB259-overexpressing plants were much more tolerant to freezing than FIB273-overexpressing ones. These results suggest that two transcripts derived from AtFIB5 have different functions, which are maintaining the photosynthesis apparatus for FIB273 and improving freezing tolerance for FIB259.
