More than only photosynthesis: chloroplasts as plant growth regulators

Centre for Research in Agricultural Genomics (CRAG)

Researchers at the Centre for Research in Agricultural Genomics (CRAG) and the University of California, Berkeley, discover that under stress conditions, chloroplasts send signals to the cell nucleus to modify plant development.

The discovery of this signalling influencing develoment, contributes to understand how endosymbiotic organelles (as mitochondria and chloroplasts) can change the overall development of a plant organism. It also describes for the first time the molecular mechanism by which plants alter their development in response to excessive light.

Microscopic image of cells of Arabidopsis thaliana seedling stem

Microscopic image of cells of Arabidopsis thaliana seedling stem. Chloroplasts in green, cell nuclei in blue.

In 1967, the American biologist Lynn Margulis formulated her famous endosymbiosis theory, explaining the origin of mitochondria and chloroplast organelles inside eukaryotic cells. These organelles, once primitive bacteria, transferred most of their own genetic material to the cell nucleus. The cell nucleus, then containing most of the cell’s DNA, became the cell’s "director" and supplier of most cellular proteins. Thanks to its acquired directing role, the nucleus is constantly sending signals towards other organelles to perform important cell functions such as division or differentiation.

The function of mitochondria and chloroplasts as cell energy producers is well known. So is the fact that these organelles can transmit to the nucleus their status and needs, through what is known as retrograde signalling. Mitochondria and chloroplasts use retrograde signalling to request from the nucleus the proteins they need for energy production. Likewise, retrograde signalling has been shown in animal cells to also be important for a variety of other cellular functions besides energy production. For example, mitochondria signalling to the nucleus modulates important processes such as cell division or tumour progression.

Elena Monte and Guiomar Martín

E. Monte and G. Martín observing seedlings in the in vitro walk-in growth chamber

In the study, published in Nature Communications, the team led by the CSIC researcher at CRAG, Elena Monte, describes for the first time that the effects of retrograde signalling in plants go far beyond what had been described so far, being able to modulate the overall plant development. "We were surprised to discover that the signals coming from the chloroplasts have the ability to modify the development of the plant, circumventing the nucleus," explains Guiomar Martín, PhD student at CRAG and first author of the article. "Just as mitochondria signalling to the nucleus regulates key processes in animals, we now know that in plants the chloroplasts can regulate development through a new mechanism that we have been able to describe at the molecular level," adds the principal investigator of the study, Elena Monte.

References:

Guiomar Martín, Pablo Leivar, Dolores Ludevid, James M. Tepperman, Peter H. Quail & Elena Monte “Phytochrome and retrograde signalling pathways converge to antagonistically regulate a light-induced transcriptional network” Nature Communications. May, 2016

Related articles