Two Coiled-Coil Proteins, WEB1 and PMI2, Suppress the Signaling Pathway of Chloroplast Accumulation Response that Is Mediated by Two Phototropin-Interacting Proteins, RPT2 and NCH1, in Seed Plants.

Noriyuki Suetsugu,Masamitsu Wada

doi:10.3390/ijms18071469

Abstract

Chloroplast movement is induced by blue light in a broad range of plant species. Weak light induces the chloroplast accumulation response and strong light induces the chloroplast avoidance response. Both responses are essential for efficient photosynthesis and are mediated by phototropin blue-light receptors. J-DOMAIN PROTEIN REQUIRED FOR CHLOROPLAST ACCUMULATION RESPONSE 1 (JAC1) and two coiled-coil domain proteins WEAK CHLOROPLAST MOVEMENT UNDER BLUE LIGHT 1 (WEB1) and PLASTID MOVEMENT IMPAIRED 2 (PMI2) are required for phototropin-mediated chloroplast movement. Genetic analysis suggests that JAC1 is essential for the accumulation response and WEB1/PMI2 inhibit the accumulation response through the suppression of JAC1 activity under the strong light. We recently identified two phototropin-interacting proteins, ROOT PHOTOTROPISM 2 (RPT2) and NPH3/RPT2-like (NRL) PROTEIN FOR CHLOROPLAST MOVEMENT 1 (NCH1) as the signaling components involved in chloroplast accumulation response. However, the relationship between RPT2/NCH1, JAC1 and WEB1/PMI2 remained to be determined. Here, we performed genetic analysis between RPT2/NCH1, JAC1, and WEB1/PMI2 to elucidate the signal transduction pathway.

Highlights

Phototropins are blue-light photoreceptor kinases that mediate phototropism, leaf flattening, stomatal opening, and chloroplast movement including low light-induced chloroplast accumulation response and strong light-induced chloroplast avoidance response
J-domain protein required for chloroplast accumulation response 1 and rpt2nch1 plants are both defective in the accumulation response [12,13]
In response to 3 μmol m−2 s−1 of blue light, which induces the accumulation response in wild type, a clear avoidance response is induced in rpt2nch1 but not in jac1 (Figure 1c,d) [12]

Summary

Introduction

Phototropins (phot) are blue-light photoreceptor kinases that mediate phototropism, leaf flattening, stomatal opening, and chloroplast movement including low light-induced chloroplast accumulation response and strong light-induced chloroplast avoidance response ( referred to as the accumulation and avoidance response, respectively). These responses contribute to optimal photosynthetic light utilization at the organ/tissue, cellular, and organelle level [1,2]. In M. polymorpha, the RPT2/NCH1 ortholog MpNCH1 mediates the accumulation response, indicating that phototropin-regulated chloroplast movement is conserved in land plants [12]. We performed genetic analysis of RPT2 and NCH1 using triple or quadruple mutant plants between rpt2nch and other mutants that were implicated in the signal transduction of chloroplast movement

Results and Discussion

Arabidopsis Lines and the Growth Condition

Analyses of Chloroplast Photorelocation Movements