| Plants respond to stress and pathogen attack by synthesizing and storing defense-related proteins in the vacuole. Many of these proteins are targeted to the vacuole by virtue of sorting information residing in a C-terminal vacuolar sorting signal (ctVSS). While many studies have been conducted to identify the nature of these sorting signals, very little is known about the factors they interact with or the factors involved in the transport mechanism that delivers these proteins to the vacuole. A genetic approach has been used in Arabidopsis thaliana (L.) Heynh, to identify loci involved in the ctVSS-bearing protein transport pathway. Mutants were screened from a collection of EMS-treated Arabidopsis thaliana ecotype Columbia seeds expressing rat-preputial beta-D glucuronidase with a ctVSS from tobacco chitinase and barley lectin. Mutants cvs1 and cvs2 (for ctVSS vacuolar sorting) were identified and characterized by immunoelectron microscopy. In these mutants, barley lectin was found to be partially mislocalized in the apoplast along the cell wall and in intercellular spaces of root sections. Such results were not observed in leaf sections, indicating the identification of root specific mutants. The mutant locus of cvs1 was mapped to a contig of BACs between AtSO191 and DFR on chromosome V. Further analyses will have to be carried out to clone the cvs1 mutant locus. However, the research presented describes identification of a factor potentially involved in transporting ctVSS bearing proteins to the vacuole. |
