Plant gravitropism is a directional response to gravity stimulus which involves a complex signaling network. Ethylene, a major plant hormone, has been found to modulate gravitropism. The biosynthesis of ethylene is induced by the gravistimulus and the requirement for ethylene during gravitropism is tissue-dependent. A dual-and-opposing effects (DOE) theory is hypothesized to address the apparently contradictory inhibitory and stimulatory effects of ethylene on gravitropism. It is suggested that both stimulatory and inhibitory effects act on the same organ of a plant and co-exist at same time in a mutually opposing manner. The final outcome of gravitropic response is determined by the dynamic display of the two opposing effects. The inhibitory effect of ethylene is dominant over the expression of the stimulatory effect in light-grown hypocotyls, whereas the stimulatory effect is dominant in inflorescence stem. Each effect is also positively correlated with concentrations of ethylene and in a time-dependent manner. Forward genetic screening based on the DOE phenotype of ethylene-treated Arabidopsis has revealed a novel component in gravity signaling pathway: EGY1. Phospho-proteomics approach has been adopted to discover new components involved in ethylene signaling. Two putative ethylene response transcription factors: EIL1 and ERF110, have been identified to contain ethylene-regulated phosphorylation sites that are ethylene-dependent but EIN2-independent, strongly suggested the existence of an alternative ethylene signal pathway. Combination of the ethylene treatments with systematic profiling of phosphoproteins using functional phosphor-proteomics among Arabidopsis ethylene response mutants is able to provide more valuable information about the molecular mechanisms underlying ethylene and gravity signaling pathways.