Plant Development and Metabolism Symposium – University of Copenhagen

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Plant Development and Metabolism Symposium

Ute Höcker, University of Cologne, Germany:  

Control of plant growth and development by the light environment

Plants constantly monitor the ambient light environment in order to adapt growth, development and metabolism to the changing light conditions and seasons. To sense the light, plants have evolved several classes of photoreceptors.

Downstream of the phytochrome and cryptochrome photoreceptors, the COP1/SPA E3 ubiquitin ligase acts as a key repressor of light signal transduction. It targets a number of transcription factors, such as CONSTANS, HY5 or PRODUCTION OF ANTHOCYANIN PIGMENT2 for degradation in darkness.  I will report on our results with respect to COP1/SPA function in Arabidopsis and Physcomitrella.

Manuel Rodríguez Concepción, CRAG, Barcelona, Spain:

Specific subsets of chaperones and proteases regulate chloroplast metabolism and development

Chloroplasts are the plant’s main factory for the production of metabolites such as isoprenoids of interest as drugs, pigments, and health-promoting phytonutrients. The production of plastidial isoprenoids is limited by the activity of the enzyme DXS (deoxyxylulose 5-phosphate synthase). DXS is prone to misfolding, hence losing its enzymatically active conformation. Besides losing functionality, misfolded forms of the enzyme tend to form protein aggregates that can be toxic for the chloroplast.

Our work in Arabidopsis has revealed how plants deal with this problem. Under normal conditions, chloroplasts get rid of defective DXS proteins by degrading them using the Clp protease. However, when stress episodes such as a sudden increase in temperature cause an overaccumulation of aggregated proteins that exceeds the ability of the Clp protease to remove them, chloroplasts generate a distress signal that travels to the nucleus of the cell to activate genes encoding plastidial chaperones such as ClpB3 and Hsp21.

Once these chaperones reach the chloroplasts, they bind to the aggregates and unfold the proteins, allowing them to spontaneously fold back to their enzymatically active form. This way, plants prevent protein aggregation in chloroplasts and ensure that enough DXS activity will be available for the production of essential isoprenoids even under stress situations. Our data also show that this mechanism is conserved in tomato, where it contributes to the differentiation of chloroplasts into isoprenoid-accumulating chromoplasts during fruit ripening.