Light and Ethylene Coordinately Regulate the Phosphate Starvation Response through Transcriptional Regulation of <i>PHOSPHATE STARVATION RESPONSE1</i>

Abstract

Plants have evolved an array of adaptive responses to low Pi availability, a process modulated by various external stimuli and endogenous growth regulatory signals. Little is known about how these signaling processes interact to produce an integrated response. <i>Arabidopsis thaliana PHOSPHATE STARVATION RESPONSE1</i> (<i>PHR1</i>) encodes a conserved MYB-type transcription factor that is essential for programming Pi starvation-induced gene expression and downstream Pi starvation responses (PSRs). Here, we show that loss-of-function mutations in <i>FHY3</i> and <i>FAR1</i>, encoding two positive regulators of phytochrome signaling, and in <i>EIN3</i>, encoding a master regulator of ethylene responses, cause attenuated <i>PHR1</i> expression, whereas mutation in <i>HY5</i>, encoding another positive regulator of light signaling, causes increased <i>PHR1</i> expression. FHY3, FAR1, HY5, and EIN3 directly bind to the <i>PHR1</i> promoter through distinct <i>cis</i>-elements. FHY3, FAR1, and EIN3 activate, while HY5 represses, <i>PHR1</i> expression. FHY3 directly interacts with EIN3, and HY5 suppresses the transcriptional activation activity of FHY3 and EIN3 on <i>PHR1</i> Finally, both light and ethylene promote FHY3 protein accumulation, and ethylene blocks the light-promoted stabilization of HY5. Our results suggest that light and ethylene coordinately regulate <i>PHR1</i> expression and PSRs through signaling convergence at the <i>PHR1</i> promoter.