title: Exploring mass spectrometry technologies to decipher metabolomic shifts during the floral transition in Arabidopsis thaliana
Creators: name: Leroux, Julie
Publisher: name: The Australian National University
Year: 2023

description: As sessile organisms, plants have evolved a multitude of mechanisms to acclimate to their environment. This enables the plant to optimise development and reproduction, and fight off or resist both biotic and abiotic stresses they may encounter through their life cycles. One such mechanism is a communication system involving the release of volatile organic compounds (VOCs). VOCs are produced from different biosynthetic pathways, by nearly all plant tissues, and under diverse physiological processes, thus providing a rich complexity. VOCs are extensively studied but little is known about their biosynthesis and biological functions. With the aim of discovering new VOCs, this thesis explores various mass spectrometry (MS) methods to select compounds of interest that are involved in plant development, specifically during the floral meristem transition. The Headspace Solid Phase Micro-Extraction Gas Chromatography (HS-SPME-GM/MS) method was used throughout the thesis for VOC analysis, while a solvent extraction protocol was adopted to isolate polar and lipophilic metabolites in the last chapter. The primary objective of this thesis is to enhance our understanding of an uncharacterised signal, ACS1, that accumulates in the clb5 mutant, causing an early halt in the carotenogenesis pathway, triggering the conversion of the vegetative meristem into a floral meristem early in development in Arabidopsis thaliana. Three results chapters will contribute to achieving this goal. The aim of the first chapter is to identify distinct chemical signatures depending on the tissue type from which the VOCs are emitted from in Arabidopsis. The VOCs released by each tissue type were investigated in detail by classifying them based on their biological function and/or the chemical group. This study allowed the identification of 197 VOCs emitted by the whole plant, of which only 73 having been previously detected in Arabidopsis. Regarding VOC abundance, this study shows that VOCs were emitted with a 10-fold change in developing buds compared to the other tissues, suggesting a high metabolomic dynamic within this particular tissue. Overall, this chapter expands our knowledge of VOCs released under normal growth, which may have important role(s) in plant development beyond their functions as pollinator attractants or defence against stresses. Through an optimisation of the HS-SPME-GC/MS method, the second chapter focuses on the understanding of metabolomic shifts during floral development by identifying VOCs involved through all developmental stages. A temporal analysis determined that 4 VOCs could play a role in floral meristem transition. Additionally, a genetic approach was adopted to decipher organ speciation, involving the study of four homeotic floral gene mutants. In the last chapter, a deeper investigation was carried out into mutants in the carotenogenesis pathway to decipher the floral transition. The clb5 mutant was shown to display important remodelling of the gene regulatory system, accumulating a signal that trigger a very early floral meristem transition. The aim of this chapter is to potential signalling molecules and identify the signalling pathways in which they are involved. Consequently, the analysis of the VOCs, polar compounds, and lipophilic compounds released by the shoot apical meristem unveiled 12 unknown compounds, yet to be fully characterised, that play a role in floral transition. These findings suggest, for the first time, that carotenoids are intricately involved in the initiation of floral development. Overall, the results presented in this thesis extend our global understanding of VOC roles and their significance in plant development. Through chemical fingerprint analysis and the elucidation of the floral transition, MS technologies open up new avenues for the discovery of VOCs and their potential application in crops to enhance plant growth, yield, and protection against various stresses.