Phototropins Mediate Chloroplast Movement in Phalaenopsis aphrodite (Moth Orchid)

Abstract

Chloroplast movement is important for plants to avoid photodamage and to perform efficient photosynthesis. Phototropins are blue light receptors in plants that function in chloroplast movement, phototropism, stomatal opening, and they also affect plant growth and development. In this study, full-length cDNAs of two PHOTOTROPIN genes, PaPHOT1 and PaPHOT2, were cloned from a moth orchid Phalaenopsis aphrodite, and their functions in chloroplast movement were investigated. Phylogenetic analysis showed that PaPHOT1 and PaPHOT2 orthologs were highly similar to PHOT1 and PHOT2 of the close relative Phalaenopsis equestris, respectively, and clustered with monocots PHOT1 and PHOT2 orthologs, respectively. Phalaenopsis aphrodite expressed a moderate level of PaPHOT1 under low blue light of 5 μmol�m−2�s−1 (BL5) and a high levels of PaPHOT1 at >BL100. However, PaPHOT2 was expressed at low levels at <BL50 but expressed at high levels at > BL100. Analysis of light-induced chloroplast movements using the SPAD method indicated that orchid accumulated chloroplasts at <BL10. The chloroplast avoidance response was detectable at >BL25 and significant chloroplast avoidance movement was observed at >BL100. Virus-induced gene silencing of PaPHOTs in orchids showed decreased gene expression of PaPHOTs and reduced both chloroplast accumulation and avoidance responses. Heterologous expression of PaPHOT1 in Arabidopsis phot1phot2 double mutant recovered chloroplast accumulation response at BL5, but neither PaPHOT1 nor PaPHOT2 was able to restore mutant chloroplast avoidance at BL100. Overall, this study showed that phototropins mediate chloroplast movement in Phalaenopsis orchid is blue light-dependent but their function is slightly different from Arabidopsis which might be due to gene evolution.

Blue Light Acclimation Reduces the Photoinhibition of Phalaenopsis aphrodite (Moth Orchid)

“…It has been reported that BL could induce photo-acclimation and thus assist plants’ tolerance to high light stress [ 15 , 16 , 17 ]. We also found that BL100 upregulated phototropins and significantly induced chloroplast avoidance in moth orchids [ 7 ]. This study further indicated that BL100 treatment for 12 days (T0) enhanced photo-acclimation in moth orchids.…”

“…Leaf samples of the new fully expanded leaves (L1) were collected. The total RNA was extracted and DNase-treated, and qRT-PCR was performed for 40 cycles with KAPA SYBR FAST qPCR Master Mix (2×) Kit (Kapa Biosystems, Woburn, MA, USA), as descripted previously [ 7 ]. The primers used in this study for PCR are listed in the Supplementary Table S1 .…”

“…Phototropins play a key role in the chloroplast movement [ 5 ]. A recent study indicated that blue light induces chloroplast movement in several monocot plants such as Brachypodium , rye, wheat and barley [ 6 ], and Phalaenopsis aphrodite [ 7 ]. If excess light absorption cannot be avoided, the over-excitation of the light-harvesting complex pigments can be alleviated via the dissipation of excess light energy as heat via nonphotochemical quenching (NPQ) and manipulating the photosynthetic efficiency to enhance plant growth and significantly increase crop yield, as has been reported [ 8 , 9 , 10 ].…”

“…However, Phalaenopsis plants are usually grown in a shade curtain greenhouse environment, which still has a high light above 300 µmol m −2 s −1 , implying that orchids might suffer from a photoinhibition problem. Recently, BL receptors, phototropin 1 and 2 have been identified, and we found that at a BL greater than 25 µmol m −2 s −1 orchids started sensing high light and exhibiting chloroplast avoidance, and a significant chloroplast avoidance movement was observed at a BL greater than 100 μmol.m −2 .s −1 [ 7 ]. Clearly, the moth orchid is very sensitive to high irradiance.…”

Blue Light Mediates Chloroplast Avoidance and Enhances Photoprotection of Vanilla Orchid

“…A recent study showed that blue light induces chloroplast movement in several monocot C 3 plants [11]. In CAM moth orchids, when blue light irradiation is above 25 µmol m −2 s −1 , chloroplasts start to show avoidance movement and significant chloroplast avoidance has been found in the strong blue light of 100 µmol m −2 s −1 [12]. When extra light has been absorbed, the plant will dissipate the excessive light energy through thermal dissipation via nonphotochemical quenching (NPQ) [7,13].…”