Spiralling into Control: Shaping Architecture in Arabidopsis and Cucumber

Cucumber fruits are important global economic and gastronomic assets. Unfortunately, the emergent high-wire cultivation system that yields the most consistent high-quality cucumbers is extremely labour-intensive. The long internodes of the plant require almost daily coiling of the bottom section of each stem, and manual removal of leaves in this area. Additionally, the radial orientation of the leaves is spiral, which impedes access to the fruits during harvesting for both human and robot alike. I propose an innovative project to stably alter cucumber phyllotaxis, here defined as the vertical and horizontal arrangement of lateral organs, by exploiting the genetics of the Arabidopsis thaliana model system. In this species, loss of the transcription factors PLETHORA3 (PLT3), PLT5 and PLT7 can switch the spiral phyllotactic pattern to an opposite pattern. Yet, these shifts never occur in a stable fashion across the whole plant. Preliminary data indicate that these three proteins also affect internode length. I will exploit this knowledge using a three-way approach. First, I will quantify the phyllotaxis-related phenotypes of plt mutants in Arabidopsis and cucumber. Secondly, I will mutagenize a population of Arabidopsis plt3,5,7 triple mutants to identify genes that confer stability to the local phyllotactic shifts observed in this line. Third, I will employ DNA Affinity Purification sequencing and RNA-seq to map regulatory targets of the PLT3/5/7 proteins in the shoot to dissect the network governing PLT-mediated phyllotaxis. Altogether, my project investigates a fundamental biological problem with a promising application in cucumber breeding, and in other crops exhibiting spiral phyllotaxis.