A matter of time: regulatory events behind the synchronization of C4 and crassulacean acid metabolism in Portulaca oleracea. (19th April 2022)

• Record Type: Journal Article
• Authors: Ferrari, Renata Callegari; Kawabata, Aline Bastos; Ferreira, Sávio Siqueira; Hartwell, James; Freschi, Luciano
• Editors: Kopriva, Stanislav
• Is Part Of: Journal of experimental botany. Volume 73:Number 14(2022)
• Page Start: 4867
• Page End: 4885
• Publication Date: 2022-04-19
• Subjects: Abscisic acid -- circadian clock -- C4 photosynthesis -- crassulacean acid metabolism -- cytokinin -- drought -- facultative CAM -- Portulacaceae -- Portulaca oleracea -- purslane -- transcription factors; Botany -- Periodicals; Botany, Experimental -- Periodicals; Plant physiology -- Periodicals; 580
• DOI: 10.1093/jxb/erac163
• Languages: English
• ISSNs: 0022-0957

Abstract

Abstract: Portulaca species can switch between C4 and crassulacean acid metabolism (CAM) depending on environmental conditions. However, the regulatory mechanisms behind this rare photosynthetic adaptation remain elusive. Using Portulaca oleracea as a model system, here we investigated the involvement of the circadian clock, plant hormones, and transcription factors in coordinating C4 and CAM gene expression. Free-running experiments in constant conditions suggested that C4 and CAM gene expression are intrinsically connected to the circadian clock. Detailed time-course, drought, and rewatering experiments revealed distinct time frames for CAM induction and reversion (days versus hours, respectively), which were accompanied by changes in abscisic acid (ABA) and cytokinin metabolism and signaling. Exogenous ABA and cytokinins were shown to promote and repress CAM expression in P. oleracea, respectively. Moreover, the drought-induced decline in C4 transcript levels was completely recovered upon cytokinin treatment. The ABA-regulated transcription factor genes HB7, NFYA7, NFYC9, TT8, and ARR12 were identified as likely candidate regulators of CAM induction following this approach, whereas NFYC4 and ARR9 were connected to C4 expression patterns. Therefore, we provide insights into the signaling events controlling C4 –CAM transitions in response to water availability and over the day/night cycle, highlighting candidate genes for future functional studies in the context of facultative C4 –CAM photosynthesis. Abstract : A dynamic interplay between phytohormones, transcription factors, and the circadian clock provides strict temporal coordination of C4 and crassulacean acid metabolism gene expression in purslane under changing environmental conditions.