The role of transcription factor StBEL11 in carbon allocation and tuberization in cultivated potato differs from that known for the model Andean genotype

The transcription factor StBEL11 is known as a negative regulator of tuberization in the Andean potato (Solanum tuberosum ssp. andigena). This study focuses on its role in the common potato ssp. tuberosum by analysing transgenic lines of cv. Kamýk with down-regulated StBEL11 expression. As expected, these lines showed enhanced tuber induction on nodal segments cultivated in vitro on high-sucrose medium. However, intact plants ex vitro exhibited significantly delayed tuberization and decreased yield, which surprisingly applied especially for lines with the most enhanced in vitro tuberization. Interestingly, reduced leaf StBEL11 expression was accompanied by decreased leaf expression of the positive tuberization regulator StBEL5, but not of SP6A tuberigen. The transgenics showed increased photosynthetic activity, which was not, however, associated with non-structural carbohydrate accumulation. Unexpectedly, StBEL11 down-regulation altered assimilate allocation in favour of roots over shoots and stolons before onset of tuberization and, in lines with the strongest phenotype, also during the early stage of tuberization, which probably explains their reduced tuber yields. The unexpected differences in tuber induction and yield between andigena and tuberosum lines with down-regulated StBEL11 indicate changes in the strength/hierarchy of individual components of the tuberization regulatory network and point to the impossibility of easy knowledge transfer from Andean to cultivated potato.