Abstract
Organ detachment requires cell separation within abscission zones (AZs). Physiological studies have established that ethylene and auxin contribute to cell separation control. Genetic analyses of abscission mutants have defined ethylene-independent detachment regulators. Functional genomic strategies leading to global understandings of abscission have awaited methods for isolating AZ cells of low abundance and very small size. Here, we couple laser capture microdissection of Arabidopsis thaliana stamen AZs and GeneChip profiling to reveal the AZ transcriptome responding to a developmental shedding cue. Analyses focus on 551 AZ genes (AZ(551)) regulated at the highest statistical significance (P < or = 0.0001) over five floral stages linking prepollination to stamen shed. AZ(551) includes mediators of ethylene and auxin signaling as well as receptor-like kinases and extracellular ligands thought to act independent of ethylene. We hypothesized that novel abscission regulators might reside in disproportionately represented Gene Ontology Consortium functional categories for cell wall modifying proteins, extracellular regulators, and nuclear-residing transcription factors. Promoter-beta-glucuronidase expression of one transcription factor candidate, ZINC FINGER PROTEIN2 (AtZFP2), was elevated in stamen, petal, and sepal AZs. Flower parts of transgenic lines overexpressing AtZFP2 exhibited asynchronous and delayed abscission. Abscission defects were accompanied by altered floral morphology limiting pollination and fertility. Hand-pollination restored transgenic fruit development but not the rapid abscission seen in wild-type plants, demonstrating that pollination does not assure normal rates of detachment. In wild-type stamen AZs, AtZFP2 is significantly up-regulated postanthesis. Phenotype data from transgene overexpression studies suggest that AtZFP2 participates in processes that directly or indirectly influence organ shed.
Highlights
Organ detachment requires cell separation within abscission zones (AZs)
Other transcription factors contributing to abscission competence include the structurally related MADS-box domain proteins AGL15 and AGL18; shedding of Arabidopsis floral parts is delayed in plants overaccumulating either protein (Fernandez et al, 2000; Adamczyk et al, 2007)
Some expressed genes have been shown by others to be associated with the abscission and/or dehiscence processes, suggesting that the AZ551 population may represent a valuable source of new cell separation determinants
Summary
Organ detachment requires cell separation within abscission zones (AZs). Functional analyses of abscission-impaired mutants have identified genes that control abscission competence from the time AZ cells differentiate through the time they separate. Partial fusion of sepals in the F-box gene mutant hawaiian skirt impairs shedding of Arabidopsis floral parts in which AZs appear to differentiate normally (Gonzalez-Carranza et al, 2007b). Other transcription factors contributing to abscission competence include the structurally related MADS-box domain proteins AGL15 and AGL18; shedding of Arabidopsis floral parts is delayed in plants overaccumulating either protein (Fernandez et al, 2000; Adamczyk et al, 2007). Flowering time and a slowing of floral senescence accompany delayed abscission in plants with knocked-down levels of ACTIN-RELATED PROTEIN4 (ARP4; Kandasamy et al, 2005a). Pleiotropic phenotypes of ARP RNAi plants have been predicted to arise from aberrant gene transcription patterns caused by altered chromatin structure (Kandasamy et al, 2005b)
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