CS-21-4 - Chloroplasts ion transport mechanisms and their role in photosynthesis and organellar function
Tuesday, July 17
9:33 AM - 9:53 AM
Chloroplast ion homeostasis impacts essential processes inside the organelle such as cofactor availability, membrane potentials, and stromal and luminal pH. Consequently, the plastid’s internal ion status is critical for chloroplast development and proper function of biochemical pathways, most importantly photosynthesis. Because of the central importance of the plastid for plants, disturbances in plastid ion homeostasis often affect plant physiology as a whole. Early investigations had revealed specific ion flux mediated by ion channels and ion carriers across envelope and thylakoid membranes. However, at that time, the lack of genome sequencing and tools did not allow to identify the transport genes.
The discovery of genes encoding for three chloroplast K+/H+ exchangers from the KEA family but also of plastid ion channels from the TPK and MSL family have revived this research recently. The studies of respective plant mutants provided exciting insights into the physiological significance of K+ transport processes across the inner envelope, and the thylakoid membranes. The data combined reveal a current gap in knowledge regarding the chloroplast K+ import mechanism(s). Furthermore, a closer look at previously published plastid TPK points towards important questions regarding its membrane localization.
To overcome these limitations we established an amiRNA library tool allowing for forward genetics on chloroplast-targeted gene products coupled to ionomic studies on intact isolated chloroplasts. Supported by transcriptomics we have started to characterize gene candidates for chloroplast K+ importers. Lastly, older and our own physiological studies indicate that K+ loss from the chloroplast contributes to decreased photosynthetic efficiency in glycophytes during early stages of salt-stress. We therefore envision to gain a holistic understanding of the chloroplasts K+ transport network and design plants with higher photosynthetic performance under salt stress by carefully modulating stromal and lumen K+ level. We have initiated a first phase to test the feasibility of this endeavor in crop plants.