The 5'-proximal region of the wheat Cab-1 gene contains a 268-bp enhancer-like sequence for phytochrome response.

We have previously reported that the expression of the wheat Cab-1 gene is subject to phytochrome regulation and a 1.8-kb 5' upstream sequence of this gene is sufficient for the regulated expression. To delineate sequences for the phytochrome response we analyzed a series of 5' deletion mutants as well as chimeric gene constructs comprising different sequences of the Cab-1 upstream region in transgenic tobacco seedlings. We found that a deletion mutant containing a 357-bp 5' upstream sequence still exhibits maximal levels of phytochrome-regulated expression. A 268-bp enhancer-like element, located between -89 and -357, is responsible for the phytochrome response of the Cab-1 gene; sequences upstream from -357 to -843 and downstream from -124 to +1100 are probably not involved. Finally, we show that the Cab-1 mRNA stability is not regulated by phytochrome.