Comparative analyses between shade-avoider and shade-tolerant species: the role of phytochrome B
[EN] Plants sense the presence of competing neighboring vegetation (shade) as a change in light quality (i.e., a reduced ratio of red to far-red light), a signal perceived by the phytochrome photoreceptors, which act as light-inducible molecular switches. Responses to shade are generally referred to...
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| Format: | master thesis |
| Publication Date: | 2022 |
| Country: | España |
| Institution: | Universitat Politècnica de València (UPV) |
| Repository: | RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia |
| Language: | English |
| OAI Identifier: | oai:riunet.upv.es:10251/180713 |
| Online Access: | https://riunet.upv.es/handle/10251/180713 |
| Access Level: | Open access |
| Keyword: | Phytochrome interacting factors Vegetation proximity Shade avoidance syndrome (SAS) Shade-tolerance Arabidopsis thaliana Cardamine hirsuta Phytochrome-A Phytochrome-B Fitocromo-B Fitocromo-A Tolerancia a la sombra Proximidad de vegetación Factores de interacción de fitocromos Respuesta de evasión a sombra BIOQUIMICA Y BIOLOGIA MOLECULAR Máster Universitario en Biotecnología Molecular y Celular de Plantas-Màster Universitari en Biotecnologia Molecular i Cel·lular de Plantes |
| Summary: | [EN] Plants sense the presence of competing neighboring vegetation (shade) as a change in light quality (i.e., a reduced ratio of red to far-red light), a signal perceived by the phytochrome photoreceptors, which act as light-inducible molecular switches. Responses to shade are generally referred to as the shade avoidance syndrome (SAS) and involve changes in growth and development. In Arabidopsis thaliana, SAS responses include increased hypocotyl elongation, reduced accumulation of photosynthetic pigments or flowering induction. Genetic analyses in A. thaliana indicate that the photostable phytochrome B (phyB) is the major phytochrome controlling the shade-induced hypocotyl elongation, and the photolabile phytochrome A (phyA) has an antagonistic negative role in this same response. The SAS is initiated, at least partly, by the inhibition of the interaction of active phyB with various Phytocrome interacting factors (PIFs), which results in rapid changes in the expression of dozens of Phytocrome rapidly regulated (PAR) genes, several of which are instrumental for implementing the SAS responses. Genetic analyses indicate that PIFs, proteins of the bHLH family of transcription factors, act as positive players of the hypocotyl SAS responses; and PIF7 is the key PIF, with minor contributions of PIF4 and PIF5, regulating the shade-induced hypocotyl elongation. Additional genetic analyses demonstrated positive, negative and complex roles in SAS regulation for several PAR genes encoding transcriptional regulators, including the negative regulators long Hypocotyl IN FR1 (HFR1) and elongated Hypocotyl5 (HY5). In contrast with A. thaliana, other species have evolved to tolerate plant shade (e.g., those naturally growing in the forest floors). When shade is perceived, shade-tolerant species lack the characteristic stem or hypocotyl elongation response to "escape" from shaded conditions. To understand shade tolerance, we are working with Cardamine hirsuta, an A. thaliana relative that has emerged as a powerful model system for making comparative trait analyses, because it has a shade-tolerant habit (i.e., its hypocotyls do not elongate in response to simulated shade). Using a genetic approach, we showed that the lack of shade-induced hypocotyl response in this species is caused by the enhanced activity of phyA and HFR1, two components already known to repress the SAS in A. thaliana. Therefore, shade avoidance and shade tolerance, despite representing opposite adaptive strategies to vegetation proximity, appear to share molecular mechanisms and/or genetic components, although working in different ways. GOAL. The general objective of this master project proposal is to understand how shade tolerance genetically and molecularly works. To do so, we aim to get a more complete genetic map of the components that regulate this adaptive strategy by identifying mutants in C. hirsuta with altered levels and activities in specific light signaling components identified as having a role in SAS control in A. thaliana, likely controlling also shade tolerance. Previous results and rationale. - In the shade avoider A. thaliana, phyA, phyB, PIF4, PIF5, PIF7, HFR1 and HY5 act as regulators of the shade-induced hypocotyl elongation response. Our genetic and molecular analyses showed that phyA, HFR1, PIF7 and HY5 (Qin & Martinez-Garcia, unpublished data) are required for implementing shade tolerance in C. hirsuta. We hypothesize that other A. thaliana SAS regulators, such as phyB, might also have a role in implementing shade tolerance in C. hirsuta. To address this task, we will further characterize how phyB levels affect the shade-induced hypocotyl elongation in the reference species A. thaliana. We will also explore if photoreceptor activities of C. hirsuta were substantially different to those of A. thaliana, as previously suggested. |
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