GENETIC AND MOLECULAR ANALYSIS OF LIGHT-REGULATED PLANT DEVELOPMENT

Light regulates many physiological and developmental events in plants through the action of multiple sensory pigment systems. Although our u nderstanding of the regulatory photoreceptors, including phytochromes (that principally absorb red and far-red energy) and blue light recept ors, has advanced considerably in the recent past, the mechanisms of l ight signal transduction in higher plants are poorly understood. To un ravel the molecular events associated with light-regulated plant devel opment, a large number of photomorphogenic mutants have been isolated in several different plant species, including Arabidopsis, cucumber, t omato, pea, Brassica and Sorghum, which are either impaired in normal perception of light signal (photoreceptor mutants) or are affected in some specific or a sub-set of phenotypic traits (signal transduction m utants). Their physiological and molecular analysis is proving to be v aluable in (1) assigning specific function to discrete phytochrome spe cies, (2) elucidation of elements that constitute the transduction pat hway downstream of signal perception, and (3) determining how differen t photosensory systems regulate many diverse responses. The progress m ade in the analysis of photomorphogenic mutants, as reviewed in this a rticle, clearly indicates that multiple photoreceptors, either of the same or different class, interact through an intricate network of sign al transduction pathways to finally determine the light-dependent phen otype of both monocots and dicots.