Light signaling pathways regulating early plant development: an evo-devo approach

Among several factors regulating early plant development, light plays a crucial role. In seed plants just after germination, the presence or absence of light determines the morphology of the developing seedling. The presence of light initiates photomorphogenesis in which plants undergo several developmental changes like inhibition of hypocotyl elongation, apical hook opening, cotyledon expansion and greening. Most of the photoreceptors and light-signaling transducers regulating these processes have been identified and well-studied, especially in Arabidopsis thaliana. Here we provide insights into some recent developments in the molecular regulation of seedling de-etiolation and chloroplast biogenesis. In the past few years several reports have enhanced our understanding of light-regulated development in algae and the bryophytes. In this review we highlight the key light-regulated mechanisms governing development in the simple unicellular algae Chlamydomonas reinhardtii . Further, we consolidate the current information about the role of light in regulating growth and development in the liverwort Marchantia polymorpha and the moss Physcomitrium patens. We finally discuss the conservation of the light signalling machinery in all these photosynthetic organisms.