Role of the Arabidopsis peptide transporter AtOPT6 in heavy metal detoxification and plant -pathogen interaction

AtOPT6, is a member of oligopeptide transport ( OPT) gene family. In Arabidopsis thaliana, there are nine members in the OPT gene family that are thought to be involved in peptide transport. Expression analysis using promoter-GUS transgenic lines showed that AtOPT6 is expressed predominantly in the vascular tissues of vegetative organs including roots, hypocotyl, cotyledons and leaves and in the developing ovules, filament tissues and funiculi in reproductive organs. Spatial and temporal expression of AtOPT6 correlates with transport of peptides in the major sink tissues indicating that this transporter may be involved in long distance transport of peptides to provide organic nitrogen to the developing plant organs.;Over-expression of AtOPT6 leads to cadmium hyper-sensitivity and higher accumulation of cadmium and phytochelatins in root tissues. opt6 mutant plants exhibited 10-fold less bacterial growth and the leaves showed minimal chlorosis when infected with the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) as compared with wild-type control plants. This difference in bacterial population was abolished when opt6 mutant plants were infected with a Pst DC3000 strain lacking coronatine biosynthesis. Therefore, AtOPT6 might be involved in the transport of coronatine, a phytotoxin that causes chlorosis in the infected tissue. In addition, the opt6 mutant plants also showed less susceptibility when infected with both cyst (Heterodera glycines) and root-knot ( Melidogyne incognita) nematode. AtOPT6 mediated transport of various Arabidopsis CLAVATA3/ENDOSPERM SURROUNDING REGION-like (CLE-like) and nematode secreted peptides when expressed in Xenopus. Nematode secreted peptides mimic plant CLEs to induce differentiation of root cells to form the feeding site and assist nematodes in obtaining nutrients for growth and proliferation in infected root tissues. Expression of AtOPT6 increased during the early stages of both cyst and root-knot nematode infection in and around the developing feeding sites.;Collectively, these data suggest two possible functions for AtOPT6 during nematode parasitism: AtOPT6 may transport nutrients in the form of peptides into the feeding site developed by the nematodes or AtOPT6 transports plant CLEs or nematode secreted peptides into the infected root cells and these peptides induce root differentiation to form the feeding site.