Distant Relatives: TOR Protein Regulates Cell Growth in Plants and Animals

Two such different organisms as plants and humans developed from a common precursor cell. Traces of this over one-billion-year kinship remain anchored in the genetic material of both organisms. An international team of plant researchers led by Dr Markus Wirtz and Prof. Dr Rüdiger Hell of Heidelberg University has looked more closely into one such trace – the TOR protein. In human and animal cells, TOR acts as a signal generator that controls both survival and cell growth. The Heidelberg researchers have now discovered how this protein also functions as a growth regulator in plants.

The TOR protein sets the stage for growth only when there is sufficient sulphate available to nourish the plant. The information on the sulphate content of the soil is transmitted to the cells via sugar but not via amino acids, which are the building blocks of proteins. "This finding can contribute to cultivating nutrient-efficient crops which can then be used in sustainable agriculture," states Prof. Hell.

But knowledge about the TOR protein's regulatory function is important not only for plant researchers. Medical researchers have long been investigating the growth regulator. Whereas TOR is active in healthy human cells only in the presence of sufficient amino acids, an out-of-control TOR protein in cancer cells contributes to rampant tumour proliferation. That is why TOR is a critical target for tumour medications.

In cooperation with researchers from the German Cancer Research Center (DKFZ), the Heidelberg plant researchers proved that despite millions of years of evolution, nothing has really changed about the basic function of TOR as a growth regulator. "Since separation from the common precursor, only the regulation mechanisms of the TOR protein have adapted to the different ways of life of humans and plants," explains Markus Wirtz.

The current findings, which are equally important for plant and animal studies, are the result of a collaboration of researchers from a number of fields. This "innovative type of basic cross-organism research", as Prof. Hell characterises it, is conducted at the Centre for Organismal Studies at Heidelberg University. Ruperto Carola's "Cellular Quality Control and Damage Response" Collaborative Research Centre (CRC 1036), which is funded by the German Research Foundation, also made a significant contribution to the endeavour. Prof. Hell and Dr Wirtz of Heidelberg University and Prof. Dr Aurelio A. Teleman of the DKFZ are coordinating the work.

The results of this research were published in the journal “Nature Communications”.