Biosynthesis and role of strigolactones in the phosphate starvation response in tomato

Strigolactones (SLs) are a class of newly identified plant hormones regulating shoot branching and root architecture under phosphate (P) shortage. However, under P shortage SLs are also secreted from the plant root into the rhizosphere, where SLs are a host signal for AM fungi and the rhizosphere microbiome. However, SLs also induce the seed germination of parasitic plants, such as broomrape, which negatively affects crop yield. In this thesis the fact is discussed that there are many different SLs that vary in as well as between plant species and that a better understanding of their biological relevance is required. Therefore, RNAseq was used to elucidate the role of SLs in P deficiency induced transcriptional changes in tomato. This showed that P starvation responsive genes are less induced in a SL biosynthetic mutant. Indeed, a substantial number of the P starvation induced transcriptional changes, such as the remodeling of lipid metabolism and plant hormone biosynthesis, depend on the presence of SLs. The RNAseq data were also used to identify unknown biosynthetic genes, using co-expression analysis. Two cytochrome P450 enzymes responsible for the production of tomato SLs were identified and characterized. The results obtained in this thesis will brings us a step closer to the possibility to apply the knowledge of SLs for crop breeding in order to control parasitic weeds and improve microbiome recruitment