Exploring the functions of WHIRLY1 in photosynthesis

CH Foyer

Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK

Chloroplasts are major sensors of environmental change, particularly stress perception. We have been studying the functions of WHIRLY1 in this regard, with a particular focus on leaf development, photosynthesis and stress tolerance. The WHIRLY family of ssDNA binding proteins form tetramers and larger oligomeric structures in chloroplasts and mitochondria. In the nucleus WHIRLY1 acts as a transcription activator for pathogen-related gene expression and as a repressor for the kinesin-like protein 1 that modulates telomere length. In chloroplasts, WHIRLY1 is required for plastid genome stability and plastid gene transcription. We have characterised WHIRLY1 functions in barley using RNAi-knockdown lines (W1-1, W1-7 and W1-9) that have very low levels of HvWHIRLY1 transcripts. Leaves of the WHIRLY1-deficient plants establish photosynthesis more slowly than the wild type, but otherwise are similar to the wild type, Photosynthesis rates were similar in all lines but W1-1, W1-7 and W1-9 leaves had significantly more chlorophyll and less sucrose than the wild type. Transcripts encoding specific sub-sets of chloroplast-localised proteins such as ribosomal proteins, subunits of the RNA polymerase and the thylakoid NADH and cytochrome b6/f complexes were much more abundant in the W1-7 leaves than the wild type. While susceptibility of aphid infestation was similar in all lines, the WHIRLY1-deficient plants showed altered responses to drought and to nitrogen deficiency, maintaining higher photosynthetic CO2 assimilation rates than the wild type under stress conditions.