Abstract
Precise and timely regulation of organ separation from the parent plant (abscission) is consequential to improvement of crop productivity as it influences both the timing of harvest and fruit quality. Abscission is tightly associated with plant fitness as unwanted organs (petals, sepals, filaments) are shed after fertilization while seeds, fruits, and leaves are cast off as means of reproductive success or in response to abiotic/biotic stresses. Floral organ abscission in Arabidopsis has been a useful model to elucidate the molecular mechanisms that underlie the separation processes, and multiple abscission signals associated with the activation and downstream pathways have been uncovered. Concomitantly, large-scale analyses of omics studies in diverse abscission systems of various plants have added valuable insights into the abscission process. The results suggest that there are common molecular events linked to the biosynthesis of a new extracellular matrix as well as cell wall disassembly. Comparative analysis between Arabidopsis and soybean abscission systems has revealed shared and yet disparate regulatory modules that affect the separation processes. In this review, we discuss our current understanding of the transcriptional regulation of abscission in several different plants that has improved on the previously proposed four-phased model of organ separation.
Highlights
The plant architecture is continuously being shaped and reshaped by assembly and modification of cell wall materials that consist mainly of celluloses, hemicelluloses, pectins, lignin, and structural proteins
As abscission is a developmentally programmed process that is readily influenced by environmental changes, studies with intact plant systems (Arabidopsis floral organs) in controlled environments and the explant systems are used to uncover the molecular mechanisms associated with abscission because they provide the platform that generates reproducible and statistically sound data
In the soybean abscission system, roles of ANT and AIL6 appear complex; as ANT and AIL6 are regulated by the AUXIN RESPONSE FACTOR 2 (ARF2) in Arabidopsis, it would appear that the ANT/AIL module may be associated with balancing between cell proliferation and differentiation in the soybean leaf abscission zone (AZ) through translating the decline in auxin that occurs at the onset of abscission (Figure 2) [12,44,102]
Summary
The plant architecture is continuously being shaped and reshaped by assembly and modification of cell wall materials that consist mainly of celluloses, hemicelluloses (cross-linking glycans), pectins, lignin, and structural proteins. Many additional signaling components including a small signaling peptide, receptor-like kinases, MAP kinases, transcription factors, and membrane traffic regulators have been shown to be critical to differing phases of separation processes [3,5,6,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34]. Plants 2019, 8, x FOR PEER REVIEW traffic regulators have been shown to be critical to differing phases of separation processes [3,5,6,15– first, The working model for abscission consists of largely four basic phases [2,4,5,7,10,12,23,30,35,36,37]: 34]. Model of organ separation (Figure 1) [2,7,12]
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