期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：9
页码：2906-2911
DOI：10.1073/pnas.1423595112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceDramatic changes in gene expression occur in abscission zones immediately prior to abscission. This study helps explain the mechanisms and emergent properties of a regulatory network that controls abscission. Two important connections are made that help explain the observed dynamic range of abscission gene expression. First, it connects a MAP kinase cascade that positively regulates abscission to a MADS-domain transcription factor, AGAMOUS-like 15 (AGL15). Second, it connects AGL15 to the expression of a receptor kinase known to control abscission. All together, the findings define a positive feedback loop that provides exponential signal amplification that starts with a receptor, goes through a MAP kinase cascade and a transcription factor, and then returns to the receptor. Abscission is the process by which plants shed unwanted organs, either as part of a natural developmental program or in response to environmental stimuli. Studies in Arabidopsis thaliana have elucidated a number of the genetic components that regulate abscission of floral organs, including a pair of related receptor-like protein kinases, HAESA and HAESA-like 2 (HAE/HSL2) that regulate a MAP kinase cascade that is required for abscission. HAE is transcriptionally up-regulated in the floral abscission zone just before cell separation. Here, we identify AGAMOUS-like 15 (AGL15; a MADS-domain transcription factor) as a putative regulator of HAE expression. Overexpression of AGL15 results in decreased expression of HAE as well as a delayed abscission phenotype. Chromatin immunoprecipitation experiments indicate that AGL15 binds the HAE promoter in floral receptacles. AGL15 is then differentially phosphorylated through development in floral receptacles in a MITOGEN-ACTIVATED PROTEIN KINASE KINASE 4/5-dependent manner. MAP kinase phosphorylation of AGL15 is necessary for full HAE expression, thus completing a positive feedback loop controlling HAE expression. Together, the network components in this positive feedback loop constitute an emergent property that regulates the large dynamic range of gene expression (27-fold increase in HAE) observed in flowers when the abscission program is initiated. This study helps define the mechanisms and regulatory networks involved in a receptor-mediated signaling pathway that controls floral organ abscission.
关键词：transcriptional regulation ; transcription factor ; protein phosphorylation ; signal transduction ; abscission
