Early gene expression events in the laminar abscission zone of abscission-promoted citrus leaves after a cycle of water stress/rehydration: involvement of CitbHLH1

Abstract

Leaf abscission is a common response of plants to drought stress. Some species, such as citrus, have evolved a specific behaviour in this respect, keeping their leaves attached to the plant body during water stress until this is released by irrigation or rain. This study successfully reproduced this phenomenon under controlled conditions (24h of water stress followed by 24h of rehydration) and used it to construct a suppression subtractive hybridization cDNA library enriched in genes involved in the early stages of rehydration-promoted leaf abscission after water stress. Sequencing of the library yielded 314 unigenes, which were spotted onto nylon membranes. Membrane hybridization with petiole (Pet)- and laminar abscission zone (LAZ)-enriched RNA samples corresponding to early steps in leaf abscission revealed an almost exclusive preferential gene expression programme in the LAZ. The data identified major processes such as protein metabolism, cell-wall modification, signalling, control of transcription and vesicle production, and transport as the main biological processes activated in LAZs during the early steps of rehydration-promoted leaf abscission after water stress. Based on these findings, a model for the early steps of citrus leaf abscission is proposed. In addition, it is suggested that CitbHLH1, the putative citrus orthologue of Arabidopsis BIGPETAL, may play major roles in the control of abscission-related events in citrus abscission zones.

Involvements of PCD and changes in gene expression profile during self-pruning of spring shoots in sweet orange (Citrus sinensis)

“…The involvement of protein biosynthesis was also supported by the induction of genes encoding translation initiation and elongation factors. This is consistent with previous reports of stimulation by protein biosynthesis within the AZ in citrus [ 52 ]. These results suggested that the specific activation of the protein metabolism within the AZ is a consequence of remodeling of protein composition coupled with the activation of hormone signaling events.…”

Role of the KNOTTED1-LIKE HOMEOBOX Protein (KD1) in regulating tomato flower pedicel abscission at early and late stages of the process

“…Previous reports showed that mobilization of the secretory pathway leads to the release of cell wall modifying enzymes to implement abscission [31,32]. Additionally, Agusti et al [28] Our analysis showed that the ABC transporter gene, an ATP-binding cassette transporter which belongs to the ABCA sub-family, was downregulated in the KD1-silenced plants compared to the WT (Fig. 6F4).…”

“…Previous reports on various abscission systems demonstrated the involvement and importance of Ca 2+ /CaM signaling in regulation of organ abscission. Thus, a cycle of water stress/rehydration, which induced citrus leaf abscission, resulted in upregulation of a CaM gene in the laminar leaf AZ at 1 h after rehydration [28].…”

Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum

“…Some research has found that hydrogen peroxide (H 2 O 2 ) acts downstream from ethylene and plays a role in the cell-wall degradation process in abscission signaling [13,14].Reactive oxygen species (ROS), including H 2 O 2 , superoxide, singlet oxygen, and the hydroxyl radical, are produced in response to environmental stress [13]. Environmental stresses (such as drought, cold stress, salt stress, and pathogen attack) are often accompanied by leaf abscission [15][16][17], but the relationship between stress and abscission is rarely studied. Excessive ROS can damage cellular components, including lipids, protein, and nucleic acids [18].…”