Flowering and dormancy are economically important traits in almond (Prunus dulcis) modulated by photoperiod and prolonged cold temperature periods. Understanding how plants control floral bud dormancy and flowering has been paramount to tree genomic investigations and breeding programs seeking to identify traits associated with regulating early and late flowering in different cultivars. Recent studies in other deciduous trees have identified that a basic leucine zipper transcription factors FD, members of phosphatidyl ethanolamine-binding protein (PEBP), DORMANCY ASSOCIATED MADS BOX (DAMs) and plant hormones such as abscisic acid as well as gibberellic acid are key regulators modulating floral bud dormancy and flowering. Their genes and other biological processes controlling flowering traits in almond have not yet been characterised. Therefore, in this thesis, I took a reverse genetic approach to identify and characterize PEBP family genes and FD genes and a transcriptomic approach to identify key hormones, metabolites and other signalling pathways that regulate floral bud dormancy and flowering. Chapter 1 contains a brief summary of the state of almond breeding and phenology and the current knowledge on genetic mechanisms regulating flowering and dormancy in Arabidopsis and different deciduous trees. In Chapter 2, gene annotation and phylogenetic analysis identified the FD gene and five PEBP family genes from the almond ‘Texas’ v2 genome. In Chapter 3, the transcriptomic of nine floral bud samples of almond ‘Nonpareil’ cultivar spanning from the middle of summer (long photoperiod) to the onset of winter (short photoperiod) were analysed. In Chapter 4, the transcriptome of almond leaves collected simultaneously with buds in chapter 4 revealed that leaves could act as a source of florigen signals, ABA signalling, carbohydrate mobilisation and production of amino acid building blocks for floral bud sinks. In the final discussion of my thesis, I highlighted that circadian rhythm and photoperiod-related genes likely promote FT expression in almond leaves yet suppress its expression in buds. The expression patterns regulating genes involved in modulating hormone biosynthesis and catabolism, flowering and dormancy (e.g., DAMs) in almond leaf and buds is contrasted with source to sink relationships. Evidence for antagonism between ABA/DAMs and GA in regulating dormancy is discussed in the context of other deciduous tree species and contrasted between almond buds and leaves. Knowledge regarding these genes and biological processes could be further utilized to validate molecular markers for identifying flowering and dormancy-related traits in almond mapping populations that can be used to identify new varieties for cultivation in a diverse range of environmental conditions.
Identification and characterisation of genes regulating flowering and dormancy in almond through transcriptomic analysis and functional complementation in Arabidopsis
Paudel, L. (Author). 2023
Western Sydney University thesis: Doctoral thesis