Global climate change, in particular rising temperatures and water scarcity, has become a huge threat for food security worldwide. Potato which belongs to the most important crop worldwide is a cool climate crop that is particularly sensitive to heat and drought stress, which have both a negative impact on tuber development. A better understanding of underlying mechanisms and the development of novel breeding tools for potato is therefore an urgent need for sustainable increases in potato production.
To achieve this goal an integrated approach combining physiology, biochemistry and molecular biology was followed to analyse the impact of elevated temperatures on source-sink relations of potato plants. Our results showed that elevated temperatures impair photosynthetic assimilate production and partitioning towards tubers, but stimulated shade-avoidance responses. Reduced sink strength of tubers was paralleled by decreased sucrose synthase activity and expression under elevated temperatures. Heat-mediated inhibition of tuber growth coincided with a decreased expression of the phloem-mobile tuberisation signal SP6A, a FT homolog in potato (Hastilestari et al., 2018). Further molecular studies suggested that SP6A is not only transcriptionally regulated, but also post-transcriptionally by a putative miRNA (named SES) (Lehretz et al. 2019). Importantly, the expression of this miRNA is strongly induced under elevated temperatures, when SP6A transcript abundance is decreased. Altering expression of the SP6A-specific siRNA or ectopic expression of codon-optimized SP6A overcame the heat-induced inhibition of tuberisation, indicating that SP6A is a master regulator of source-to-sink relations (Lehretz et al., 2019).
In addition to heat, drought causes significant effects on tuber yield. By combined manipulation of transpiration by stomata-specific overexpression of AtHxk1 and SP6A expression, we improve heat- and drought tolerance of transgenic potato plants.
The mode of action of SP6A is largely unknown. Accumulating evidences suggest that SP6A might alter meristem identity. In addition, SP6A seems to play a pivotal role in driving photoassimilates distribution in the plant, by modulating sucrose transport to the tuber sinks. This is corroborated by the finding that SP6A directly binds the SWEET sugar transporters and inhibits their sucrose efflux transport activity (Abelenda et al. 2019). Further indications for the latter role will be discussed.