Interplay between sugar and hormone signaling pathways modulate floral signal transduction

Abstract

NOMENCLATURE The following nomenclature will be used in this article: Names of genes are written in italicized upper-case letters, e.g., ABI4.Names of proteins are written in non-italicized upper-case letters, e.g., ABI4.Names of mutants are written in italicized lower-case letters, e.g., abi4.The juvenile-to-adult and vegetative-to-reproductive phase transitions are major determinants of plant reproductive success and adaptation to the local environment. Understanding the intricate molecular genetic and physiological machinery by which environment regulates juvenility and floral signal transduction has significant scientific and economic implications. Sugars are recognized as important regulatory molecules that regulate cellular activity at multiple levels, from transcription and translation to protein stability and activity. Molecular genetic and physiological approaches have demonstrated different aspects of carbohydrate involvement and its interactions with other signal transduction pathways in regulation of the juvenile-to-adult and vegetative-to-reproductive phase transitions. Sugars regulate juvenility and floral signal transduction through their function as energy sources, osmotic regulators and signaling molecules. Interestingly, sugar signaling has been shown to involve extensive connections with phytohormone signaling. This includes interactions with phytohormones that are also important for the orchestration of developmental phase transitions, including gibberellins, abscisic acid, ethylene, and brassinosteroids. This article highlights the potential roles of sugar-hormone interactions in regulation of floral signal transduction, with particular emphasis on Arabidopsis thaliana mutant phenotypes, and suggests possible directions for future research.

Regulatory roles of sugars in plant growth and development

“…The participation of ABI3 as well as ABF2 and ABF4 transcription factors has been demonstrated in sugar signal transduction, either dependent or independent of hexokinase [6,28,36,63]. In addition, more recent results indicated the interaction of cytokinins, gibberellins, jasmonic acid, salicylic acid, and brassinosteroids with sugar pathways during plant development [57,103,104]. It was suggested that the function of HXK1 is dependent on the presence of brassinosteroids, which might act downstream of HXK1 to regulate hypocotyl elongation in A. thaliana in darkness (in a glucose-dependent reaction) [104].…”

“…For example, the delivery of sucrose to the A. thaliana mutant, phyA, characterized by late flowering, accelerated the formation and flowering of the inflorescence stem [58]. As was recently reported, the crosstalk between sugar signaling and photoreceptors (as well as hormones) is required for proper transmission of the flowering signal [31,57].…”

“…Sugars (sucrose) have been found to affect the activity (and expression) of both the sucrose transporters, which are essential for the efficient transport of sugar over long distances. Sugars, as assimilates, are necessary for the initiation of flowering in plants [31,57,58]; however, recent studies have shown the regulatory role of sucrose, along with miRNA156 and Tre6P, in the regulation of the flowering process [24,59]. For example, the delivery of sucrose to the A. thaliana mutant, phyA, characterized by late flowering, accelerated the formation and flowering of the inflorescence stem [58].…”

“…Thus, nowadays, some studies have been focused on the role of sugars as scavengers of reactive oxygen species [73]. The regulatory role of sugars during plant development also results from the connections of sugar signaling pathways with other routes, including hormonal pathways, as described in the following subsection, and with nitrogen metabolism [34,37,57,63,74].…”

Transitioning to the Next Phase: The Role of Sugar Signaling throughout the Plant Life Cycle

“…Excellent reviews on the role of sugar signaling in plant development have been published in recent years. Most of these focus on specific signaling pathways or developmental processes, for example, on flowering and interaction with hormones (Matsoukas, 2014a), growth (Lastdrager et al, 2014), T6P (O'Hara et al, 2013), T6P and SnRK1 (Tsai and Gazzarrini, 2014), hexokinase (Granot et al, 2014), miRNAs (Yu et al, 2015), or SnRK1 and TOR (Baena-González and Hanson, 2017). The whole life cycle of the plant is considered here (Box 1), including step changes (such as floral transition) as well as more gradual processes (such as leaf senescence).…”