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Abstract
In plants, developmental or environmental stresses activate a suite of different phytohormones that trigger biochemical and/or morphological adaptations. The gaseous phytohormone ethylene has a major effect on the plant life cycle from germination onward. Ethylene biosynthesis is tightly regulated by external and internal cues. In etiolated seedlings of Arabidopsis and rice, various phytohormones affect ethylene biosynthesis through transcriptional and/or post-transcriptional regulation of 1-aminocyclopropane-1-carboxylic acid (ACC), ACC synthases (ACS), and ACC oxidases (ACO). This study showed strigolactone also affected ethylene biosynthesis in dark-grown rice seedlings. Strigolactone treatment altered levels of S-ADENOSYLMETHIONINE SYNTHASES (OsSAMSs) and ACC SYNTHASES (OsACSs) transcripts, which encode enzymes involved in the initial steps of ethylene biosynthesis. The application of strigolactone reduced ethylene production, however, by decreasing transcription of OsACO genes, thus negatively affecting the final step of ethylene biosynthesis. In addition, treatment with strigolactone resulted in a phenotype in which the coleoptiles of dark-grown rice seedlings were shortened, contrary to treatment with ACC. These results reveal the tight correlation between strigolactone and ethylene biosynthesis.