Effect of constitutive expression of bacterial phytoene desaturase CRTI on photosynthetic electron transport in Arabidopsis thaliana

Abstract

The constitutive expression of the bacterial carotene desaturase (CRTI) in Arabidopsis thaliana leads to increased susceptibility of leaves to light-induced damage. Changes in the photosynthetic electron transport chain rather than alterations of the carotenoid composition in the antenna were responsible for the increased photoinhibition. A much higher level of superoxide/hydrogen peroxide was generated in the light in thylakoid membranes from the CRTI expressing lines than in wild-type while the level of singlet oxygen generation remained unchanged. The increase in reactive oxygen species was related to the activity of plastid terminal oxidase (PTOX) since their generation was inhibited by the PTOX-inhibitor octyl gallate, and since the protein level of PTOX was increased in the CRTI-expressing lines. Furthermore, cyclic electron flow was suppressed in these lines. We propose that PTOX competes efficiently with cyclic electron flow for plastoquinol in the CRTI-expressing lines and that it plays a crucial role in the control of the reduction state of the plastoquinone pool.

Enrichment of provitamin A content in wheat (Triticum aestivum L.) by introduction of the bacterial carotenoid biosynthetic genes CrtB and CrtI

“…Constitutive expression of CrtI in the leaves of transgenic wheat lines OEI and OEIB was consistent with results from transgenic tobacco and Arabidopsis, resulting in a significant decrease in lutein content in parallel with a slight reduction in chlorophyll content (Misawa et al , 1993; Galzerano et al , 2014). It has been documented that the accumulation of phytoene leads to the metabolic feedback regulation of PSY and its upstream geranylgeranyl pyrophosphate synthase in the carotenoid biosynthetic pathway (Cazzonelli and Pogson, 2010).…”

Contrasting Responses of Plastid Terminal Oxidase Activity Under Salt Stress in Two C4 Species With Different Salt Tolerance

“…In this regard, Ahmad et al (2012) have reported a dramatic decline in the NDH activity in tobacco expressing PTOX from green algae (Cr-PTOX1). Furthermore, PTOX may efficiently compete with CEF for the plastoquinol (PQH 2 ) in the CRTI-expressing (carotene desaturase) lines (Galzerano et al, 2014). Joët et al (2002) also showed a decrease in the NDH-dependent CEF flux in tobacco transgenic lines expressing PTOX from Arabidopsis.…”

The Plastid Terminal Oxidase: Its Elusive Function Points to Multiple Contributions to Plastid Physiology

“…There are, however, conditions where PTOX seems unable to take up this mechanistic challenge. When overexpressed in tobacco lines or when having to cohabit in the thylakoid membrane with a heterologously expressed bacterial phytoene desaturase, PTOX is a strong ROS producer (41,50). Interestingly, in vitro studies recently provided further insights into the balance between the antioxidant (oxygen-reducing) and prooxidant (ROS-producing) activity of PTOX.…”

“…Because it is a poor competitor of the photosynthetic mainstream, PTOX is unlikely to be a major player in photoprotection, at least under constant and saturating light conditions. Another feature of PTOX that argues against the safety valve function is its contribution to ROS production (33,41,50,167), which may damage the photosynthetic apparatus. However, according to Li et al (84), PTOX may consume up to 10% of photochemically produced oxygen via the astaxanthin biosynthesis pathway, which would lower the oxygen partial pressure in the cell and consequently decrease ROS production (84).…”