The Tomato's Molecular Armour: Scientists Create A Cold-Resistant Variety Without Sacrificing Growth

Researchers at CRAG have discovered that increasing glycosylated sterol levels in tomato improves cold tolerance by stabilizing cell membranes and activating hormonal signalling pathways.

• Researchers at CRAG have discovered that increasing glycosylated sterol levels in tomato improves cold tolerance by stabilizing cell membranes and activating hormonal signalling pathways.
• Genetically modified plants show an early response to cold stress, with greater activation of antioxidant enzymes, abiotic stress defence genes, and polyamine biosynthesis.
• The strategy does not negatively affect plant growth, opening new biotechnological possibilities for developing tomato varieties more resistant to cold.

Researchers at CRAG have taken a crucial step toward improving tomato production in cold climates. They have identified and enhanced the levels of key molecules in cell membranes, known as glycosylated sterols (GS), which not only provide the plant with tolerance to low temperatures but do so without hindering its development or growth.

The study, led by University of Barcelona scientists at CRAG Albert Ferrer and Teresa Altabella, and published in the journal Plant Physiology, opens the door to developing more robust tomato (Solanum lycopersicum) varieties.

The tomato’s Achilles heel
Due to its tropical origin, tomatoes are notoriously sensitive to cold temperatures, especially those ranging from 0 to 12 °C. The optimal growing temperature for tomato is between 20 and 28 °C, and dropping below 10–12 °C negatively affects its development.

Until now, most studies on cold resistance had focused on plants where glycosylated sterols were minor components. But in tomato, and generally in the Solanaceae family, GS are the predominant sterol form in their membranes. CRAG researchers have shown that these GS act as key sensors that detect cold stress and activate protective molecular mechanisms.

The secret of “pre-conditioning”
To test this function, the team worked with transgenic lines of the MicroTom variety. They increased GS production by overexpressing the SlSGT2 enzyme (SGT2ox plants) and decreased GS by silencing the SlSGT1 enzyme (SGT1ami plants). These two enzymes are responsible for synthesising GS. The result was clear and, according to Albert Ferrer, CRAG researcher and co-author of the study, “it’s not common to observe such clearly antagonistic phenotypes”:

• Plants with overexpression of SGT2 (SGT2ox), with increased GS levels, showed significantly higher cold tolerance.
• Plants with silenced SlSGT1 enzyme (SGT1ami), which reduced GS levels, showed increased sensitivity to cold.

The key to resistance lies in the fact that high GS levels stabilize the plasma membrane. Moreover, these glycosylated sterols give the plant a “pre-conditioned” stress response state, meaning an early response even before they are exposed to the cold.

This protective state involves early molecular activation of defences:

• Hormonal activation: Jasmonate signalling (such as JA and JA-Ile), crucial stress-response hormones, is triggered. SGT2ox tolerant plants accumulated up to 3.5 times more jasmonates than control plants.
• Defence mechanisms: This hormonal signalling prepares the plant by activating cold-response genes (SlCBF1 and SlDRCi7) and enhancing its ability to manage oxidative damage, increasing the activity of enzymes such as catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST). A higher accumulation of polyamines like putrescine was also observed, contributing to cellular protection.

Agronomic implications
The great biotechnological potential of this research lies in the fact that, unlike other genetic modifications, increasing GS had no negative effect on plant growth or development under normal cultivation conditions.

“We’ve shown that glycosylated sterols not only protect the membrane but activate a complete molecular response that prepares the plant to withstand cold”, explains Teresa Altabella, CRAG researcher and co-author of the study.

Modifying these metabolic pathways could be a viable strategy for agriculture, enabling the development of tomato varieties more resistant to cultivation in fields exposed to low temperatures or in greenhouses that do not require heating, which would translate into significant benefits in terms of yield and productivity.