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Title: Diurnal oscillations of soybean circadian clock and drought responsive genes

item GOMES, JULIANA - Embrapa
item NAKAYAMA, THIAGO - Universidade Federal De Vicosa
item BENDIX, CLAIRE - University Of California
item CELEYA, R. BRANDON - University Of California
item MOLINARI, HUGO - Embrapa-Labex
item NEPOMUCENO, ALEXANDRE - Embrapa-Labex
item Harmon, Frank

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2013
Publication Date: 1/31/2014
Citation: Gomes, J.M., Rodrigues, F.A., Fuganti-Pagliarini, R., Nakayama, T.J., Bendix, C., Celeya, R., Molinari, H.B., Nepomuceno, A.L., Harmon, F.G. 2014. Diurnal oscillations of soybean circadian clock and drought responsive genes. PLoS One. 9(1):e86402. doi:10.1371/journal.pone.0086402.

Interpretive Summary: Water limitation or drought is a major environmental stress for plants. Plants actively respond to drought stress by modifying their transcriptional program, which produces induction and repression of specific sets of genes that are considered key drought-responsive genes. The plant circadian clock, which is responsible for producing and maintaining 24-hour rhythms in many aspects of plant physiology, plays a broad role in controlling responses to the environment, including drought signals, and one of its primary means of control is regulation of transcription through the action of clock-associated transcription factors. Rhythmic gene expression produced by circadian clock regulation and the influence of diurnal light/dark signals is not well characterized for soybean, let alone the influence of drought stress on this aspect of the soybean transcriptome. This study tested whether the 24-hour rhythmic expression pattern of likely circadian clock genes was changed by drought treatment. In addition, the potential for reciprocal regulation was also evaluated by determining whether known soybean drought-responsive genes had rhythmic expression patterns, as well as the effect of drought on their rhythmic waveforms. It was found that drought modified the way soybean circadian clock genes were expressed. Drought conditions changed not only the expression levels of known drought genes, but also their 24-hour pattern of expression. These observations show that soybean plants experiencing drought conditions respond by modifying rhythmic expression of key drought response genes, which likely arises fundamental changes in their circadian clock regulation since genes for core circadian clock transcription factors also had modified expression with drought. Therefore, a complete understanding of how soybean plants response to drought demands the study of circadian clock regulation of this response.

Technical Abstract: Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts on diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicates that some connection between the drought response and the circadian clock may exists in soybean since (i) drought stress affects gene expression of circadian clock components and (ii) several stress responsive genes display diurnal oscillation in soybeans.