Chloroplast-associated molecular patterns as concept for fine-tuned operational retrograde signalling

To optimize the resource expenditure in these costly organelles and to control and adjust chloroplast metabolism, an intensive transfer of information between nucleus–cytoplasm and chloroplasts occurs in both directions as anterograde and retrograde signalling.

Regulatory feedback loops play central roles in biological processes.

we propose the term ‘chloroplast-associated molecular pattern’ which connects chloroplast performance to extrachloroplast processes such as nuclear gene transcription, posttranscriptional processing, including translation, and RNA and protein fate.

They are also required to coordinate processes among organelles and cell compartments. The need for communication between the photosynthesizing chloroplast and the extrachloroplast compartments, in particular cytosol, nucleus and mitochondrion, is easily explained by two fundamental requirements: chloroplast metabolism must cover the demand for specific metabolites and energy in development, defence and storage, and unfavourable metabolic states should be avoided.