Tissue-Autonomous Promotion of Palisade Cell Development by Phototropin 2 inArabidopsis 

Abstract

Light is an important environmental information source that plants use to modify their growth and development. Palisade parenchyma cells in leaves develop cylindrical shapes in response to blue light; however, the photosensory mechanism for this response has not been elucidated. In this study, we analyzed the palisade cell response in phototropin-deficient mutants. First, we found that two different light-sensing mechanisms contributed to the response in different proportions depending on the light intensity. One response observed under lower intensities of blue light was mediated exclusively by a blue light photoreceptor, phototropin 2 (PHOT2). Another response was elicited under higher intensities of light in a phototropin-independent manner. To determine the tissue in which PHOT2 perceives the light stimulus to regulate the response, green fluorescent protein (GFP)–tagged PHOT2 (P2G) was expressed under the control of tissue-specific promoters in the phot1 phot2 mutant background. The results revealed that the expression of P2G in the mesophyll, but not in the epidermis, promoted palisade cell development. Furthermore, a constitutively active C-terminal kinase fragment of PHOT2 fused to GFP (P2CG) promoted the development of cylindrical palisade cells in the proper direction without the directional cue provided by light. Hence, in response to blue light, PHOT2 promotes the development of cylindrical palisade cells along a predetermined axis in a tissue-autonomous manner.

Light-induced Conformational Changes of LOV1 (Light Oxygen Voltage-sensing Domain 1) and LOV2 Relative to the Kinase Domain and Regulation of Kinase Activity in Chlamydomonas Phototropin

“…Phototropin (phot) 3 is a BL sensor and was determined to be a receptor for the phototropic response (4). Afterward, phot was shown to mediate chloroplast relocation (5), stomata opening (6), leaf flattering (7), and leaf photomorphogenesis (8). All of these responses serve to optimize the efficiency of photosynthetic activities.…”

A Dominant Mutation in the Light-Oxygen and Voltage2 Domain Vicinity Impairs Phototropin1 Signaling in Tomato

“…Physiological analyses with Arabidopsis mutants lacking phot1 and phot2 have revealed that, in addition to regulating the hypocotyl curvature of seedlings toward BL (Huala et al, 1997;Christie et al, 1998), phototropins also regulate a diverse range of responses in flowering plants (Christie and Murphy, 2013;Hohm et al, 2013). These responses include chloroplast movements , nuclear positioning (Iwabuchi et al, 2007), stomatal opening (Kinoshita et al, 2001), sun tracking (Inoue et al, 2008b), leaf expansion (Ohgishi et al, 2004), leaf movements (Inoue et al, 2005), leaf photomorphogenesis (Kozuka et al, 2011), leaf flattening (Sakamoto and Briggs, 2002), and the rapid inhibition of the growth of etiolated hypocotyls (Folta and Spalding, 2001).…”

Rapid Severing and Motility of Chloroplast-Actin Filaments Are Required for the Chloroplast Avoidance Response inArabidopsis

“…These include phototropic responses, chloroplast movement, stomatal opening, leaf flattening, and palisade cell development (Huala et al, 1997;Jarillo et al, 2001;Kagawa et al, 2001;Kinoshita et al, 2001;Sakai et al, 2001;Kozuka et al, 2011). With regard to chloroplast movement, phot1 and phot2 redundantly mediate the accumulation response, whereas phot2 alone mediates the avoidance response in Arabidopsis (Jarillo et al, 2001;Kagawa et al, 2001;Sakai et al, 2001).…”