Phosphoinositides Play Differential Roles in Regulating Phototropin1- and Phototropin2-Mediated Chloroplast Movements in Arabidopsis

Abstract

Phototropins are UVA/blue-light receptors involved in controlling the light-dependent physiological responses which serve to optimize the photosynthetic activity of plants and promote growth. The phototropin-induced phosphoinositide (PI) metabolism has been shown to be essential for stomatal opening and phototropism. However, the role of PIs in phototropin-induced chloroplast movements remains poorly understood. The aim of this work is to determine which PI species are involved in the control of chloroplast movements in Arabidopsis and the nature of their involvement. We present the effects of the inactivation of phospholipase C (PLC), PI3-kinase (PI3K) and PI4-kinase (PI4K) on chloroplast relocations in Arabidopsis. The inhibition of the phosphatidylinositol 4,5-bisphospahte [PI(4,5)P2]-PLC pathway, using neomycin and U73122, suppressed the phot2-mediated chloroplast accumulation and avoidance responses, without affecting movement responses controlled by phot1. On the other hand, PI3K and PI4K activities are more restricted to phot1- and phot2-induced weak-light responses. The inactivation of PI3K and PI4K by wortmannin and LY294002 severely affected the weak blue-light-activated accumulation response but had little effect on the strong blue-light-activated avoidance response. The inhibitory effect observed with PI metabolism inhibitors is, at least partly, due to a disturbance in Ca2+ (c) signaling. Using the transgenic aequorin system, we show that the application of these inhibitors suppresses the blue-light-induced transient Ca2+ (c) rise. These results demonstrate the importance of PIs in chloroplast movements, with the PI(4,5)P2-PLC pathway involved in phot2 signaling while PI3K and PI4K are required for the phot1- and phot2-induced accumulation response. Our results suggest that these PIs modulate cytosolic Ca2+ signaling during movements.

The impact of temperature on blue light induced chloroplast movements in Arabidopsis thaliana

“…After acclimation to low temperatures the calcium release from internal stores increases [64]. It should be noted that phototropin2 is mainly responsible for calcium release from internal stores [62,21].…”

“…Calcium ions were proposed as secondary messengers in this process [19,20]. Recent data suggest that cytosolic calcium signaling is modulated by phosphoinositides [21,22]. Several proteins involved in chloroplast movement are associated with the organization of the actin cytoskeleton: CHUP1, KAC (1,2) and THRUMIN1, while others may be involved in signaling: PMI1, JAC1, PMI2, WEB1, PMI15 (for review see [23,24] [25].…”

Clues to the signals for chloroplast photo‐relocation from the lifetimes of accumulation and avoidance responses

“…However, despite gaining considerable knowledge about the photoreceptors and the actin system, the signals that connect them are largely unknown. Based on experiments with inhibitors, a leading candidate has been calcium (Kadota and Wada ; Banaś et al ; Aggarwal et al ; Kong and Wada ). Gabryś et al .…”

The Arabidopsis DREB2 genetic pathway is constitutively repressed by basal phosphoinositide-dependent phospholipase C coupled to diacylglycerol kinase

“…It was shown to diminish PI-PLC in vivo activity during osmotic stress (Takahashi et al, 2001; Parre et al, 2007; Ghars et al, 2012), heat stress (Liu et al, 2006), cold stress (Vergnolle et al, 2005), gravistimulation (Perera et al, 2001), and to diminish calcium oscillation in guard cells in response to ABA (Staxen et al, 1999). Recently, it was used to show PI-PLC involvement in phototropic gene expression (Salinas-Mondragon et al, 2010) and in blue light-mediated chloroplast movements (Aggarwal et al, 2013). It was also shown to inhibit a basal PI-PLC activity in Coffea arabica cells (Ramos-Díaz et al, 2007).…”