Arabidopsis class II TPS controls root development and confers salt stress tolerance through enhanced hydrophobic barrier deposition.

The mechanism of conferring salt tolerance by AtTPS9 involves enhanced deposition of suberin lamellae in the Arabidopsis root endodermis, resulting in reduction of Na transported to the leaves. Members of the class I trehalose-6-phosphate synthase (TPS) enzymes are known to play an important role in plant growth and development in Arabidopsis. However, class II TPSs and their functions in salinity stress tolerance are not well studied. We characterized the function of a class II TPS gene, AtTPS9, to understand its role in salt stress response and root development in Arabidopsis. The attps9 mutant exhibited significant reduction of soluble sugar levels in the leaves and formation of suberin lamellae (SL) in the endodermis of roots compared to the wild type (WT). The reduction in SL deposition (hydrophobic barriers) leads to increased apoplastic xylem loading, resulting in enhanced Na content in the plants, which explains salt sensitivity of the mutant plants. Conversely, AtTPS9 overexpression lines exhibited increased SL deposition in the root endodermis along with increased salt tolerance, showing that regulation of SL deposition is one of the mechanisms of action of AtTPS9 in conferring salt tolerance to Arabidopsis plants. Our data showed that besides salt tolerance, AtTPS9 also regulates seed germination and root development. qRT-PCR analyses showed significant downregulation of selected SNF1-RELATED PROTEIN KINASE2 genes (SnRK2s) and ABA-responsive genes in the mutant, suggesting that AtTPS9 may regulate the ABA-signaling intermediates as part of the mechanism conferring salinity tolerance.