PhD Advisor: Professor Salim Al-Babili

Abstract:
Apocarotenoids are carotenoid-derived molecules that regulate plant growth and response to biotic and abiotic stresses, and are precursors of the two phytohormones strigolactones (SLs) and abscisic acid (ABA). My PhD thesis investigated how modulation of carotenoid precursor levels through the overexpression of key biosynthetic genes affects apocarotenoid metabolism in roots and elucidated the biological function of a key component of the signaling pathway of the apocarotenoid zaxinone. 

Constitutive overexpression of the carotenoid biosynthetic gene LYCOPENE-β-CYCLASE (LCYB) in tobacco and tomato altered carotenoid, apocarotenoid and phytohormone levels in root tissues, increasing ABA and reducing SL content. These changes were associated with enhanced root growth and biomass, reduced arbuscular mycorrhizal (AM) colonization, and lower stimulation of Striga seed germination, thus highlighting the impact of LCYB on belowground traits.

To elucidate the signaling mechanisms of the apocarotenoid zaxinone, I characterized a rice Receptor-Like Protein Kinase (OsRLPK) encoded by a hub gene in zaxinone-induced transcriptional networks. CRISPR/Cas9-generated Osrlpk mutants displayed growth defects, increased SL accumulation, impaired mycorrhization, and reduced responsiveness to zaxinone, demonstrating that OsRLPK is an essential component of zaxinone signaling. In addition, the reduced sensitivity of Osrlpk mutants to brassinolide (BL) together with global proteomic and phosphoproteomic analyses revealed an additional role of OsRLPK in the signaling of the hormone brassinosteroid (BR). Protein-protein interaction assays showed that OsRLPK interacts with OsBAK1 and that this interaction is modulated by zaxinone, supporting a model in which OsRLPK acts as a signaling hub linking zaxinone and BR pathways.

Together, these findings identify apocarotenoids as central regulators of plant growth, tightly linked to hormonal and metabolic networks. This highlights the potential of bioactive apocarotenoids as targets for improving crop performance and yield.

Bio:
I received my M.Sc. in Plant Biotechnology from the University of Turin (Italy) in 2020. I then joined the BioActives Lab at KAUST, where I am currently doing a Ph.D. in Plant Science under the mentorship of Prof. Salim Al-Babili. During my Ph.D., my research has focused on elucidating the function and signaling mechanisms of growth-promoting apocarotenoids in different crop species.