Blue- and red-light regulation and circadian control of gene expression of S-adenosylmethionine decarboxylase in Pharbitis nil

The abundance of mRNA for S-adenosylmethionine decarboxylase (SAMDC) (EC 4.1.1.50) in leaves of Pharbitis nil is regulated by light. The level of this mRNA fluctuated dramatically, peaking 45 min after light exposure and then decreasing rapidly to a very low level. The half-life of the SAMDC mRNA was estimated by using actinomycin D to be approximately 30 min, which partly accounts for the rapid decline in the mRNA level after the peak of light induction is reached. The mRNA level for the SAMDC gene increased after light exposure from red, green, blue or UV light, but not after far-red light exposure. The short irradiation of red light increased the expression of the SAMDC gene and this induction was reverted by subsequent far-red light irradiation. The immediate blue light illumination after the initial red light exposure resulted in a further increase in the SAMDC mRNA level. These results indicate that both the blue light photoreceptor- and phytochrome-mediated pathways are involved in the light regulation of the SAMDC gene. The transcription of the SAMDC gene was also shown to be under circadian control. (author)