Portulaca oleracea as a model for the transition between C3, C4 and CAM photosynthesis: biochemical characterization and development of stable genetic transformation protocols

• Grant number: 14/08963-5
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2014
• End date: June 30, 2015
• Field of knowledge: Biological Sciences - Botany - Pant Physiology
• Principal Investigator: Luciano Freschi
• Grantee: Paula Yumi Nagumo
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Representing CO2-concentrating mechanisms, Crassulacean acid metabolism (CAM) and C4 photosynthesis confer increased water use efficiency and minimized photorespiration, thus being especially helpful to plant growing at tropical regions. Up to now, C4-CAM facultative behavior has only been identified in three plant species, all of them belonging to Portulaca genus. Among them, Portulaca oleracea is characterized by exhibiting facultative C4-CAM photosynthesis in the leaves and facultative C3-CAM behavior in the shoot; therefore, representing a plant material particularly interesting for analyzing the biochemical, physiological, genetic, regulatory, and evolutionary mechanisms responsible for integrating these distinct photosynthetic behaviors (C3, C4, and CAM) in the same organism. A particularly interesting strategy to be carried out in this species might be the silencing and overexpression of key components of these CO2-concentrating mechanisms, such as enzymes and regulatory proteins. Therefore, studies targeted to optimize in vitro regeneration protocols to facilitate the future use of recombinant DNA technologies for the production of transgenic plants of P. oleracea are particularly important for establishing more consistent approaches in the study of the occurrence of C3, C4 and CAM photosynthesis in the same species. Based on this scenario, this project aims to contribute to the establishment of P. olearecea as a genetic model for studies on the transition between C3, C4, and CAM photosynthesis. First, protocols for in vitro regeneration and stable genetic transformation via co-cultivation with Agrobacterium tumefasciens will be established. In parallel, a detailed characterization of the ideal water supply regime for the induction, maintenance, and reversion of CAM behavior in leaf and shoot tissues will also be performed. To achieve this, P. oleracea plants will be exposed to distinct water supply regimes and, then, their leaf and shoot titratable acidity and organic acid (malate, citrate, isocitrate, and fumarate) levels will be determined and compared to the diel fluctuations in soluble sugars (sucrose, fructose, and glucose) and starch. Finally, the morphological alterations associated with the C4-to-CAM and C3-to-CAM transitions in leaf and shoot tissues, respectively, will also be characterized. Altogether, these approaches might provide important subsidies for the adoption of P. olearacea as a genetic model for studies on the transition between C3, C4 and CAM photosynthesis, whose understanding might possibly be used in the future for improving water use efficiency in economically important crop species. (AU)