The consortium behind ADAPT has been studying how environmental pressures affect potato tuber formation’s signaling systems as part of their efforts to create multiple-stress-tolerant potatoes.

Research from several partner labs has improved our knowledge of how the “master regulator” of tuberization functions and has led to the identification of a potential gene for a crucial stage in the process. Breeders can use these genes to create better potato cultivars that can continue to produce even in challenging environmental circumstances.

“Tuber induction is initiated in the leaves, where day length controls the production of the tuberization signal SP6A. This mobile protein enters the phloem, which also supports the transport of sugars from leaves to below-ground organs, and travels to the underground stems or stolons. Here, it activates tuber identity genes which initiates tuber formation,” according to a recent press release.

It is commonly known that conditions like high temperatures prevent the SP6A signal from being produced and that this inhibition is what causes the yield loss that occurs during heat stress. The mechanism of yield loss under these conditions is still unclear because SP6A seems to be less influenced by other stresses.

“SP6A is a member of a family of proteins with roles in a diverse range of developmental processes such as flowering, branching, and root development. Other family members include TFL1B and TFL1C which in related species such as tomato control the number and location of flowers. It is now known that for SP6A to induce tuber formation, it needs to cooperate with other proteins from the bZIP transcription factor family, held together in a complex scaffolded by 14-3-3 proteins. This complex binds specific stretches of DNA to activate tuber identity genes. To understand whether TFL1B and TFL1C also regulate tuber formation, ADAPT researchers generated plants in which the expression of these genes was reduced. These plants formed earlier tubers and had higher tuber yields both under optimal and stressful conditions. In a series of molecular and biochemical experiments conducted by Universitat Wien, CRAG, and James Hutton Institute, researchers discovered that TFL1B and TFL1C could replace SP6A in protein complexes with bZIP transcription factors and 14-3-3 proteins. However, when SP6A was replaced different genes were activated and tuberization was not induced. This indicates that TFL1B and TFL1C compete with SP6A in plant tissues to reduce tuberization. When TFL1B or TFL1C gene expression is reduced less SP6A is required for tubers to form. In the reduced TFL1B and TFL1C lines the expression of genes encoding GERMINS was highly up-regulated. In a different set of plants where the GERMIN3 gene was up-regulated, tuberization occurred sooner and yields were higher. It was found that GERMIN3 regulates the transfer of sugars to the developing tuber, an essential process identified more than 20 years ago,” the scientists mentioned.

These results have significantly advanced ADAPT’s consortium understanding of the mechanisms signaling potato tuberization and how tuber formation can be blocked by adverse environmental conditions. TFL1B, TFL1C, and GERMINS were identified as main targets for the generation of new cultivars that exhibit yield maintenance under adverse conditions. Such targets can be exploited either using marker-assisted breeding or new precision breeding technologies.

The Horizon 2020 EU project Accelerated Development of multiple-stress tolerAnt PoTato (ADAPT), in which Europatat is participating, aims to understand the signaling pathways for single and combined abiotic stresses to the selection of potato cultivars more resilient to climate change.