Conceal the signals

Abstract

Phosphate deficiency promotes SL biosynthesis and secretion into soil. Using a hydroponic sorghum growth system that enables convenient manipulation of phosphate conditions, the researchers observed upregulation of genes for SL biosynthesis and signalling, and ABC transporters, under conditions of phosphate deficiency. They then focused on two plasma membrane transporters (ABCG36 and ABCG48) that are expressed predominantly in root epidermal cells, because these are induced by both phosphate deficiency and root SL treatment.

ABCG36 and ABCG48 export SLs effectively, as shown by expression systems based on yeast and Xenopus laevis oocytes. ABCG36 and ABCG48 were therefore designated as sorghum SL transporter 1 (SbSLT1) and SbSLT2, respectively. Arabidopsis lines that stably express SbSLT1 or SbSLT2 displayed an enhanced tolerance of high-concentration SLs, and higher SL secretion from root tissues. This SL export activity seems to be unique to SbSLT1 and SbSLT2, as other ABCG proteins in sorghum do not have it.