Phytochrome-induced intercellular signalling activates CAB:luciferase gene expression

The phytochrome-induced expression pattern of the chlorophyll a/b binding protein (cab) gene was studied using a cab2::luciferase reporter transgene in the tobacco cotyledon. The role of developmentally regulated competence, cooperativity among cells and signal propagation was investigated by red-light microbeam irradiation of distinct areas of the cotyledon. Even with a minimal fluence, the response was not restricted to the irradiated cells. Following irradiation of the cotyledon base, the luciferase activity revealed a robust propagation of activating signals to areas that had not received a light stimulus. The acropetal outspread formed distinct expression patterns depending on the site of the irradiation, The combination of imaging luciferase activity in living seedlings and microbeam microscopy provides significant experimental evidence of how cellular light perception and intercellular signalling contribute to the cab gene expression pattern.