Abstract - Carotenoids are essential for plant photosynthesis. But, the story doesn’t end there: volatile apocarotenoids, carotenoid oxidative cleavage products, are important plant fragrances and semiochemicals, and some are believed to be so-called ‘apocarotenoid signals’ (ACS), regulating plant processes. Apocarotenoids are formed either by carotenoid cleavage dioxygenases (CCDs) or non-enzymatic oxidation. But what is the split between CCD and non-enzymatically-derived volatile apocarotenoids? What factors affect carotenoid catabolism and volatile apocarotenoid accumulation?
To study volatile apocarotenoid metabolism in planta, I developed a solid phase microextraction (SPME) gas chromatography mass spectrometry (GC/MS) protocol for analysing volatile apocarotenoids. Then, I applied SPME-GC/MS to analyse Arabidopsis volatile apocarotenoid profiles in Col-0 and ccd-loss-of-function single and double mutants. I also examined the Arabidopsis ccr2 mutant. Ccr2 accumulates linear carotenoids not typically observed in Arabidopsis, and I’ve found it also emits exotic volatile apocarotenoids. I also did a more-targeted study of volatile apocarotenoids and CCD1 and CCD4 activity during senescence.
Using untargeted SPME-GC/MS volatile metabolomics, I reveal a remarkable breadth of known and putative volatile apocarotenoids in Arabidopsis, and provide evidence that CCDs barely contribute to volatile apocarotenoid production, producing non-volatile apocarotenoids instead. Volatile apocarotenoids are formed mainly via carotenoid non-enzymatic oxidation. My results highlight the importance of maintaining carotenoid turnover in leaves: when CCD activity is lost, volatile apocarotenoid production increases markedly. Despite previous studies suggesting it, I found little evidence for CCD-derived ACS contributing to either the ccr2 phenotype or retarding senescence.
Biography - John completed a Bachelor of Philosophy at the ANU in 2013, after doing Honours research in Professor Michael Djordjevic’s lab examining phytohormone responses to C-terminal Encoded Peptides (CEPs) in Medicago truncatula. John also completed many undergraduate projects with Professor Barry Pogson’s group, and returned to the Pogson Group in 2014 to commence his PhD. This research was supported by an Australian Research Training Program Scholarship and a Grains Research and Development Corporation Grains Industry Research Scholarship.
His research aims to better-understand apocarotenoid metabolism and biology. Most of his work has been at the ANU Joint Mass Spectrometry Facility and John has also collaborated with various RSB and CSIRO researchers interested in volatile measurements. John is also collaborating with GC/MS technologists at Monash University. After his PhD, John will remain in Canberra to consider his options. His medium-long-term goal is to run a consultancy assisting researchers and entrepreneurs to transfer and commercialise research.