Characterization of the restricted sucrose export 1 (freezing tolerance 1) mutant reveals a function of a pectate lyase-like gene in the establishment of the sugar translocation pathway in Arabidopsis thaliana

Abstract

We previously reported isolation and characterization of an Arabidopsis freezing tolerance 1 (frt1) mutant that showed mature-leaf-specific enhancement of the degree of freezing tolerance due to soluble sugar accumulation. Here, we showed that this mutant shows "restricted sucrose export" phenotypes. Thus, we renamed this mutant rsx1. As reported previously, the rsx1 mutant showed mature-leaf-specific accumulation of transitory starch. We also showed that GUS expression in the rosettes of RSX1promoter:GUS plants occurs in a basipital mode along the leaf vein, suggesting the correlation between RSX1 expression and the expression of source leaf functions. In accordance with this, ¹⁴C-sucrose-feeding experiments revealed that rsx1 plants are restricted in the sucrose export out of mature leaves. We also present some transmission electron micrographs, which strongly supported our hypothesis that RSX1 is a genetic factor involved in the establishment of sucrose translocation pathway in the source leaves of A. thaliana.