CIRCADIAN CLOCK ASSOCIATED 1 gates morning phased auxin response in Arabidopsis thaliana.

Circadian clock controls plant behaviors to anticipate day-night switch and keeps plant fitness. Here, we reported that plant response to auxin is also strictly governed by clock. The amplitude of auxin-responsive gene expressions gradually declined from morning to the dusk, and then enhanced from dusk to dawn. Plants with defects in both CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and its closest homologue LATE ELONGATED HYPOCOTYL (LHY) (cca1 lhy) showed comparable responses to auxin at different time points in consecutive days, suggesting that CCA1 and LHY were required for gating auxin responses. Moreover, CCA1/LHY physically interacted with the core transcriptional repressors (Aux/IAA proteins), which might further modulate plant sensitivity to auxin. Taken together, we demonstrate that the central morning phased circadian oscillator CCA1 plays a pivotal role in gating auxin response.

A point-to-point protein-protein interaction assay reveals the signaling interplays among plant hormones and environmental cues.

As sessile organisms, plants must properly coordinate their growth and developmental programs with changes in the environment. The integration of exogenous environmental cues with endogenous plant hormone responses often occurs through physical protein-protein interactions (PPIs). However, a comprehensive PPI network that mediates environmental and hormonal responses has not been established. In this study, we initially cloned 113 phytohormone-related genes and 29 light signaling components of Arabidopsis and then individually tested their mutual interactions (in total 2,655 tests) using a yeast-two-hybrid approach to ultimately identify 141 interactions. Based on these interaction results, we next revealed the signaling cross talk between jasmonate and abscisic acid by characterizing the JAZ1-PYL4 and JAZ1-ABI1 interactions. Thus, we generated a useful resource for the community to explore the molecular mechanisms underlying signaling interactions between plant hormones and/or with light.