Reduced expression of a vesicle trafficking-related ATPase SKD1 decreases salt tolerance in Arabidopsis

In this study we present the functional characterisation of SKD1 (suppressor of K+ transport growth defect) in salt tolerance of higher plants. SKD1 participates in endosome-mediated protein sorting and expression of SKD1 is salt-induced in Na+ storage cells of halophyte ice plant. Transgenic Arabidopsis with reduced SKD1 expression were generated by expressing AtSKD1 in antisense orientation. Relative root growth rate of antisense seedlings was slower than that of wild-type seedlings under salt treatment. The Na+/K+ ratio doubled in the antisense seedlings compared with the wild-type seedlings indicating a loss in Na+/K+ homeostasis. The PSII activity dropped following one week of salt-stress in antisense plants whereas wild-type plants maintained normal activity. Upon germination, transgenic seedlings developed multiple roots where each root had lower density of lateral roots. Application of 1-naphthaleneacetic acid restored the ability of transgenic seedlings to form lateral roots. Expression profiling analyses revealed that expressions of one stress-related kinase, several salt-induced transcription factors and one auxin efflux transporter were altered in antisense seedlings. With decreased expression of SKD1, plants experience a reduced salinity response and altered root development indicating the importance of intracellular vesicular trafficking in both auxin-mediated plant growth and in maintaining ion homeostasis under salt stress.