PLASTID MOVEMENT IMPAIRED1 and PLASTID MOVEMENT IMPAIRED1-RELATED1 Mediate Photorelocation Movements of Both Chloroplasts and Nuclei

Abstract

Organelle movement and positioning play important roles in fundamental cellular activities and adaptive responses to environmental stress in plants. To optimize photosynthetic light utilization, chloroplasts move toward weak blue light (the accumulation response) and escape from strong blue light (the avoidance response). Nuclei also move in response to strong blue light by utilizing the lightinduced movement of attached plastids in leaf cells. Blue light receptor phototropins and several factors for chloroplast photorelocation movement have been identified through molecular genetic analysis of Arabidopsis (Arabidopsis thaliana). PLASTID MOVEMENT IMPAIRED1 (PMI1) is a plant-specific C2-domain protein that is required for efficient chloroplast photorelocation movement. There are two PLASTID MOVEMENT IMPAIRED1-RELATED (PMIR) genes, PMIR1 and PMIR2, in the Arabidopsis genome. However, the mechanism in which PMI1 regulates chloroplast and nuclear photorelocation movements and the involvement of PMIR1 and PMIR2 in these organelle movements remained unknown. Here, we analyzed chloroplast and nuclear photorelocation movements in mutant lines of PMI1, PMIR1, and PMIR2. In mesophyll cells, the pmi1 single mutant showed severe defects in both chloroplast and nuclear photorelocation movements resulting from the impaired regulation of chloroplast-actin filaments. In pavement cells, pmi1 mutant plants were partially defective in both plastid and nuclear photorelocation movements, but pmi1pmir1 and pmi1pmir1pmir2 mutant lines lacked the blue light-induced movement responses of plastids and nuclei completely. These results indicated that PMI1 is essential for chloroplast and nuclear photorelocation movements in mesophyll cells and that both PMI1 and PMIR1 are indispensable for photorelocation movements of plastids and thus, nuclei in pavement cells.

Shining Light on the Function of NPH3/RPT2-Like Proteins in Phototropin Signaling

“…Polymerization of cp-actin requires the action of CHLOROPLAST UNUSUAL POSITIONING1 (CHUP1; Oikawa et al, 2003) and KINESIN-LIKE PROTEIN FOR ACTIN-BASED CHLOROPLAST MOVEMENT (KAC) proteins (Suetsugu et al, 2010). PLASTID MOVEMENT IMPAIRED1 (PMI1) also is required to stabilize cp-actin filaments (Suetsugu et al, 2015). Consequently, cp-actin formation, and thus chloroplast accumulation and avoidance movement, are impaired in chup1, pmi1, and kac1 kac2 mutants.…”

Ferns, mosses and liverworts as model systems for light‐mediated chloroplast movements

“…These factors are involved in the light-regulation of cp-actin filaments (Kodama et al 2010;Ichikawa et al 2011). The C2 domain protein PLASTID MOVEMENT IMPAIRED 1 (PMI1) has a pivotal role in the accumulation of cp-actin filaments and chloroplast movement in mesophyll cells (DeBlasio et al 2005;Suetsugu et al 2015) (Fig. 2).…”

“…2). In pavement cells, PMI1 and a homolog PMI1-RELATED 1 redundantly mediate the avoidance response of plastids (Suetsugu et al 2015). THRUMIN1 is an actin-bundling protein and interacts with cp-actin filaments in vivo (Whippo et al 2011;Kong et al 2013a) (Fig.…”

Dynamic Changes in Plant Nuclear Organization in Response to Environmental and Developmental Signals

“…Nuclear movement occurs in multiple plant cell types and developmental processes, as well as in response to both biological and mechanical stimuli (Griffis et al, 2014, and references therein). Several recent papers have focused on two nuclear movement events: nuclear photorelocation (Kawashima and Berger, 2015;Suetsugu et al, 2015;Iwabuchi et al, 2016;Suetsugu et al, 2016aSuetsugu et al, , 2016b and male germ unit migration in pollen tubes Zhou et al, 2015c). In addition, nuclei have been traced during root-hair cell death, in collet root hairs, and during gamete fusion (Kawashima and Berger, 2015;Sliwinska et al, 2015;Tan et al, 2016).…”

“…Avoidance movement is dependent upon both nuclear-adjacent chloroplasts and chloroplast-adjacent actin filaments (cp-actin; Higa et al, 2014). C2-domain proteins PMI1 and PMIR1 have also been implicated in cp-actin-dependent nuclear photorelocation in pavement cells (Suetsugu et al, 2015).…”