A New Role for SAG12 Cysteine Protease in Roots of Arabidopsis thaliana

International audience ; Senescence associated gene (SAG) 12, which encodes a cysteine protease isconsidered to be important in nitrogen (N) allocation to Arabidopsis thaliana seeds.A decrease in the yield and N content of the seeds was observed in the ArabidopsisSAG12 knockout mutants (sag12) relative to the wild type (Col0) under limited nitrogennutrition. However, leaf senescence was similar in both lines. To test whether SAG12is involved in N remobilization from organs other than the leaves, we tested whetherroot N could be used in N mobilization to the seeds. Root architecture, N uptakecapacity and 15N partitioning were compared in the wild type and sag12 under eitherhigh nitrogen (HN) or low nitrogen (LN) conditions. No differences in root architectureor root N uptake capacity were observed between the lines under HN or LN. However,under LN conditions, there was an accumulation of 15N in the sag12 roots comparedto the wild type with lower allocation of 15N to the seeds. This was accompanied by anincrease in root N protein contents and a significant decrease in root cysteine proteaseactivity. SAG12 is expressed in the root stele of the plants at the reproductive stage,particularly under conditions of LN nutrition. Taken together, these results suggest anew role for SAG12. This cysteine protease plays a crucial role in root N remobilizationthat ensures seed filling and sustains yields when nitrogen availability is low.