THE CA DOMAIN OF RESPIRATORY COMPLEX I IS INVOLVED IN PHOTORESPIRATION AND IS REQUIRED FOR EMBRYOGENESIS

SOTO DEBORA; CORDOBA JUAN PABLO; MARCHETTI, MARIA FERNANDA; BARTOLI C; PAGNUSSAT G; EDUARDO JULIAN ZABALETA

Mar del Plata

Congreso; LI Reunión Anual SAIB; 2015

In Arabidopsis thaliana there are five gamma carbonic anhydrase proteins, called CA1, CA2, CA3, CAL1 and CAL2. All these proteins are subunits of the respiratory complex I and form, with the exception of CA3, a domain (CA domain) in the membrane arm of mitochondrial complex I. None of the single mutants shows any visible phenotype under normal conditions. In order to investigate the physiological role of the CA domain, we performed crosses to obtain different double mutants. The ca2cal1 and ca2cal2 double mutants show a growth retardation phenotype in normal air. However, this phenotype is rescued by cultivating plants in a high CO2 atmosphere. Moreover, under photorespiratory conditions, carbon assimilation is reduced and glycine accumulates, which suggests a photorespiratory imbalance. These results strongly suggest that the CA domain of plant complex I contributes to sustain an efficient photosynthesis at ambient conditions. On the other hand, ca1ca2 double mutants present an embryo lethal phenotype due to strong respiratory problems triggering ROS accumulation. Furthermore, ca1ca2 embryos accumulate abnormal oil bodies during embryogenesis. Dry seeds are collapsed, however are able to germinate two weeks later than normal. Indeed, double knockout seedlings die most likely due to oxidative stress. The ca2 single mutants contain 80% reduction of complex I. Silencing both, CA1 and CA2 genes, causes an even stronger reduction in complex I, however seeds are viable. These results suggest that ca1ca2 double mutants might contain undetectable amounts of complex I triggering the lethal phenotype. Taken into consideration the phenotype of all these double mutants, a model of the CA domain composition is presented.