Involvement of the chloroplast signal recognition particle cpSRP43 in acclimation to conditions promoting photooxidative stress in Arabidopsis.

In this study, we have investigated the role of the CAO gene (coding for the chloroplast recognition particle cpSRP43) in the protection against and acclimation to environmental conditions that promote photooxidative stress. Deficiency of cpSRP43 in the Arabidopsis mutant chaos has been shown previously to lead to partial loss of a number of proteins of the photosystem II (PSII) antennae. In addition, as reported here, mutant plants have lower growth rates and reduced lignin contents under laboratory conditions. However, chaos seedlings showed significantly higher tolerance to photooxidative stress under both tightly controlled laboratory conditions and highly variable conditions in the field. This greater tolerance of chaos plants was manifested in less photooxidative damage together with faster growth recovery in young seedlings. It was also associated with a lower production of H2O2, lower ascorbate levels and less induction of ascorbate peroxidases. Under field conditions, chaos exhibited better overall photosynthetic performance and had higher survival rates. Expression of the CAO gene may be regulated by a light-dependent chloroplastic redox signalling pathway, and was inhibited during acclimation to high light and chilling temperatures, simultaneously with induction of ascorbate peroxidases. It is concluded that the presence/absence of the CAO gene has an impact on photo-produced H2O2, lignification in the hypocotyls and on the plant's susceptibility to photooxidative stress. Therefore, regulation of the CAO gene may be part of the plant's system for acclimation to high light and chilling temperatures.