CONICET | Buscador de Institutos y Recursos Humanos

The photomorphogenic signal: an essential component of photoautotrophic life. Plants need light as a source of information and as a source of energy for photosynthesis. To monitor environmental light conditions, plants are equipped with several families of photoreceptors, the cryptochromes, the phytochromes and the LOV-domain bearing photoreceptors. While phytochromes perceive light most effectively in the red/far-red region of the spectrum, cryptochromes and LOV photoreceptors detect blue and UV-A light. Downstream these photoreceptors, plants have evolved sophisticated transcriptional networks that mediate metabolic and developmental changes in response to light. These light-regulated processes include seed germination, seedling photomophogenesis, greening, shade avoidance and photoperiodic response. Greening and chloroplast biogenesis are promoted after light exposure. Phytochromes and cryptochromes bring a lot of changes to initiate this biogenesis, which include the induction of photosynthesis-related genes at the transcriptional level, the import of nuclear-encoded proteins and the establishment of a thylakoid network fully assembled with photosynthetic electron transport complexes. Furthermore, these photoreceptors affect the synthesis of chlorophyll and other photosynthetic accessory pigments; modifying the photosynthetic apparatus properties as a result of light quality perception. On the other hand, phytochromes .are also involved in the induction of the Rubisco small subunit, a key enzyme of the Calvin Cycle. Light quality plays an important role in modulating the photosynthetic characteristics. It regulates chlorophyll degradation, modulates photosystem stoichiometry and the activity of the ROS scavenging system. In this chapter, we will focus on the role of the photomorphogenic signal to trigger the synthesis of photosynthetic genes and pigments during the greening process and later on, during photosynthetic plant development. Themes: 1) Generalities about the photomorphogenic process 2) Photoreceptors: Phytochromes, cryptochromes, LOV domain photoreceptors 3) The role of the circadian clock in photomorphogenic development 4) Light and chloroplast development 5) The regulation of Chlorophyll synthesis by light 6) The transcriptional regulation of Lhc genes by light 7) Transcriptional regulation of rbcS genes by light Key points: We will like to focus on the regulation of gene expression by light and how it impacts in photosynthetic plant development