A matter of time: regulatory events behind the synchronization of C-4 and crassulacean acid metabolism in Portulaca oleracea

Author(s)

Ferrari, Renata Callegari ; Kawabata, Aline Bastos ; Ferreira, Savio Siqueira ; Hartwell, James ; Freschi, Luciano

• Document type: Journal article
• Source: Journal of Experimental Botany; v. N/A, p. 19-pg., 2022-04-19.

Abstract

A dynamic interplay between phytohormones, transcription factors, and the circadian clock provides strict temporal coordination of C(4)and crassulacean acid metabolism gene expression in purslane under changing environmental conditions. Portulaca species can switch between C-4 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 C-4 and CAM gene expression. Free-running experiments in constant conditions suggested that C-4 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 C-4 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 C-4 expression patterns. Therefore, we provide insights into the signaling events controlling C-4-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 C-4-CAM photosynthesis. (AU)

• FAPESP's process: 16/04755-4 - Exploring C4 and Crassulacean Acid Metabolism (CAM) compatibility within a single organism: changes in global transcriptional profile, hormonal regulation, and tissue localization of key C4 and CAM components in Portulaca oleracea
• Grantee: Renata Callegari Ferrari
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)