Transcriptional and post-translational control of chlorophyll biosynthesis by dark-operative protochlorophyllide oxidoreductase in Norway spruce

Abstract

Unlike angiosperms, gymnosperms use two different enzymes for the reduction of protochlorophyllide to chlorophyllide: the light-dependent protochlorophyllide oxidoreductase (LPOR) and the dark-operative protochlorophyllide oxidoreductase (DPOR). In this study, we examined the specific role of both enzymes for chlorophyll synthesis in response to different light/dark and temperature conditions at different developmental stages (cotyledons and needles) of Norway spruce (Picea abies Karst.). The accumulation of chlorophyll and chlorophyll-binding proteins strongly decreased during dark growth in secondary needles at room temperature as well as in cotyledons at low temperature (7 °C) indicating suppression of DPOR activity. The levels of the three DPOR subunits ChlL, ChlN, and ChlB and the transcripts of their encoding genes were diminished in dark-grown secondary needles. The low temperature had minor effects on the transcription and translation of these genes in cotyledons, which is suggestive for post-translational control in chlorophyll biosynthesis. Taking into account the higher solubility of oxygen at low temperature and oxygen sensitivity of DPOR, we mimicked low-temperature condition by the exposure of seedlings to higher oxygen content (33%). The treatment resulted in an etiolated phenotype of dark-grown seedlings, confirming an oxygen-dependent control of DPOR activity in spruce cotyledons. Moreover, light-dependent suppression of mRNA and protein level of DPOR subunits indicates that more efficiently operating LPOR takes over the DPOR function under light conditions, especially in secondary needles.

Global gene expression analysis in etiolated and de-etiolated seedlings in conifers

“…Electron micrograph of the chloroplast in the DARK grown seedlings shows formation of thylakoids in Scots pine (Fig 2). Synthesis of chlorophyll in dark by pine and spruce is also reported by earlier investigations [14, 15, 37]. Higher expression of ANTHOCYANINLESS 2 ( ANL2 ), a transcription factor which is involved in the accumulation of anthocyanin and root development [48], was detected under DARK in both species.…”

Molecular Mechanisms Preventing Senescence in Response to Prolonged Darkness in a Desiccation-Tolerant Plant

“…DPOR is less regulated in darkness: in C. lanceolata, one gene encoding a DPOR subunit is induced slightly, while the genes encoding the other two subunits are repressed slightly; in P. abies, all three genes are induced (Stolárik et al, 2017;Xue et al, 2017). However, the chlorophyll content in both gymnosperm species decreased to a greater extent than in H. rhodopensis (Stolárik et al, 2017;Xue et al, 2017).…”

“…In H. rhodopensis, one LPOR-encoding gene is repressed 4-fold and another is induced 2-fold in darkness. In other angiosperms, such as Arabidopsis and the gymnosperms Norway spruce (Picea abies) and Chinese fir (Cunninghamia lanceolata), LPOR is down-regulated in darkness (Stolárik et al, 2017;Xue et al, 2017). DPOR is less regulated in darkness: in C. lanceolata, one gene encoding a DPOR subunit is induced slightly, while the genes encoding the other two subunits are repressed slightly; in P. abies, all three genes are induced (Stolárik et al, 2017;Xue et al, 2017).…”

“…In other angiosperms, such as Arabidopsis and the gymnosperms Norway spruce (Picea abies) and Chinese fir (Cunninghamia lanceolata), LPOR is down-regulated in darkness (Stolárik et al, 2017;Xue et al, 2017). DPOR is less regulated in darkness: in C. lanceolata, one gene encoding a DPOR subunit is induced slightly, while the genes encoding the other two subunits are repressed slightly; in P. abies, all three genes are induced (Stolárik et al, 2017;Xue et al, 2017). However, the chlorophyll content in both gymnosperm species decreased to a greater extent than in H. rhodopensis (Stolárik et al, 2017;Xue et al, 2017).…”

The enigmatic loss of light‐independent chlorophyll biosynthesis from an Antarctic green alga in a light‐limited environment

“…200% air saturation) at 17 m, where UWO241 is found. This is significant because, as noted earlier, the Achilles’ heel of DPOR is its oxygen‐sensitive iron−sulfur cluster (Yamazaki et al ., ; Ueda et al ., ; Stolárik et al ., ), whereas LPOR is insensitive to oxygen. If the high dissolved oxygen content of Lake Bonney inhibits the functioning of DPOR, then one would presume that there would be no deleterious effect resulting from a mutation that knocked out the DPOR pathway.…”