Deletion of chloroplast NADPH-dependent thioredoxin reductase results in inability to regulate starch synthesis and causes stunted growth under short-day photoperiods

Abstract

Plastid-localized NADPH-dependent thioredoxin reductase C (NTRC) is a unique NTR enzyme containing both reductase and thioredoxin domains in a single polypeptide. Arabidopsis thaliana NTRC knockout lines (ntrc) show retarded growth, especially under short-day (SD) photoperiods. This study identified chloroplast processes that accounted for growth reduction in SD-acclimated ntrc. The strongest reduction in ntrc growth occurred under photoperiods with nights longer than 14h, whereas knockout of the NTRC gene did not alter the circadian-clock-controlled growth of Arabidopsis. Lack of NTRC modulated chloroplast reactive oxygen species (ROS) metabolism, but oxidative stress was not the primary cause of retarded growth of SD-acclimated ntrc. Scarcity of starch accumulation made ntrc leaves particularly vulnerable to photoperiods with long nights. Direct interaction of NTRC and ADP-glucose pyrophosphorylase, a key enzyme in starch synthesis, was confirmed by yeast two-hybrid analysis. The ntrc line was not able to maximize starch synthesis during the light period, which was particularly detrimental under SD conditions. Acclimation of Arabidopsis to SD conditions also involved an inductive rise of ROS production in illuminated chloroplasts that was not counterbalanced by the activation of plastidial anti-oxidative systems. It is proposed that knockout of NTRC challenges redox regulation of starch synthesis, resulting in stunted growth of the mutant lines acclimated to the SD photoperiod.

Thioredoxin f1 and NADPH-dependent thioredoxin reductase C have overlapping functions in regulating photosynthetic metabolism and plant growth in response to varying light conditions

“…1B). In the western blots of Figure 1B, a Trx f antibody was used that gives similar signals with Trx f1 and Trx f2 (Thormählen et al, 2013), indicating that Trx f1 is the predominant Trx f isoform in Arabidopsis.As previously reported, trxf1 (Thormählen et al, 2013) and ntrc single mutants (Pérez-Ruiz et al, 2006;Lepistö et al, 2013) showed no or moderate growth phenotypes, respectively, when grown in an 8-h photoperiod at 160 mmol photons m -2 s -1 light intensity ( Fig. 2B; Supplemental Table S1).…”

NADPH Thioredoxin Reductase C and Thioredoxins Act Concertedly in Seedling Development

“…Further evidence showed the participation of NTRC in the redox regulation of enzymes that were known previously to be Trx regulated. This is the case for ADP-Glc pyrophosphorylase (AGPase), a key enzyme of starch biosynthesis (Michalska et al, 2009;Lepistö et al, 2013) and of enzymes of the chlorophyll biosynthesis pathway (Richter et al, 2013;Pérez-Ruiz et al, 2014). These results suggest that chloroplast redox regulation depends on the cross talk of both Fdx/FTR/Trx and NTRC redox systems and, hence, is more complex than anticipated previously.…”

Redox- and Reactive Oxygen Species-Dependent Signaling into and out of the Photosynthesizing Chloroplast

“…O 2 $ 2 production in isolated thylakoids depends on the photoperiod under which the plants are grown (Michelet et al, 2013). This difference is abolished upon the addition of NADPH (Michelet et al, 2013) and in mutants affected in NADPH-dependent TRX reductase C (Lepistö et al, 2013).…”