Letting Go is Never Easy: Abscission and Receptor‐Like Protein Kinases

Abstract

Abscission is the process by which plants discard organs in response to environmental cues/stressors, or as part of their normal development. Abscission has been studied throughout the history of the plant sciences and in numerous species. Although long studied at the anatomical and physiological levels, abscission has only been elucidated at the molecular and genetic levels within the last two decades, primarily with the use of the model plant Arabidopsis thaliana. This has led to the discovery of numerous genes involved at all steps of abscission, including key pathways involving receptor-like protein kinases (RLKs). This review covers the current knowledge of abscission research, highlighting the role of RLKs.

Core Mechanisms Regulating Developmentally Timed and Environmentally Triggered Abscission

“…A lot of recent attention has been given to activation of cell wall-modifying enzymes that hydrolyze the middle lamella of the abscission zone as the implied mechanism of cell separation (Niederhuth et al, 2013a(Niederhuth et al, , 2013bLiu et al, 2013). Our findings strongly suggest that while drought triggers abscission, water is required for abscission to occur.…”

“…Abscission is the process enabling plants to discard unwanted organs in response to environmental stimuli or developmental timing (Tudela and Primo-Millo, 1992;Agustí et al, 2012;Liljegren, 2012;Niederhuth et al, 2013a). Abscission occurs at distinct boundaries, called abscission zones, that are laid down as the associated organ develops.…”

Four shades of detachment: Regulation of floral organ abscission

“…Furthermore, the transcriptome analysis of floral receptacles in the hae hsl2 mutant compared to the wild type showed that the expression of cell wall loosening or hydrolytic enzymes (e.g., PGs, cellulases, and EXPs) was suppressed less than that of wax and/or suberin synthesis genes (>10 -fold less than in wild type), which suggests that in addition to IDA-HAE/HSL2 signaling pathway, complete organ separation requires the coordinated actions of genes associated with cell wall loosening (Phase 3) and the genes that may aid in the deposition of a modified extracellular matrix and the formation of a protective layer (Phase 4). 45,46 The transcriptome analysis unraveled invaluable information on the downstream cascades of IDA-HAE/HSL2-mediated signaling, however it should be noted that the sampling from floral receptacles may compromise true signaling events in the AZ due to a potential baseline level of noise that can make inter-gene expression comparisons problematic.…”

ASYMMETRIC LEAVES1 regulates abscission zone placement in Arabidopsis flowers

“…Genetic analysis in Arabidopsis has been particularly productive in revealing factors that activate the cell separation phase of floral organ abscission [1],[2]. Less is known about the regulatory circuits that control abscission zone differentiation at the boundaries between the outer floral organs and underlying receptacle [3],[4].…”