Antisense Expression of the Peptide Transport Gene AtPTR2-B Delays Flowering and Arrests Seed Development in Transgenic Arabidopsis Plants

Abstract

Previously, we identified a peptide transport gene, AfPTRZ-B, from Arabidopsis fhaliana that was constitutively expressed in all plant organs, suggesting an important physiological role in plant growth and development. To evaluate the function of this transporter, transgenic Arabidopsis plants were constructed expressing antisense or sense AfPTRZ-B. Genomic Southern analysis indicated that four independent antisense and three independent sense AtPTRZ-B transgenic lines were obtained, which was confirmed by analysis of the segregation of the kanamycin resistance gene carried on the T-DNA. RNA blot data showed that the endogenous AfPJRZ-B mRNA levels were significantly reduced in transgenic leaves and flowers, but not in transgenic roots. Consistent with this reduction in endogenous AfPTRZ-B mRNA levels, all four antisense lines and one sense line exhibited significant phenotypic changes, including late flowering and arrested seed development. These phenotypic changes could be explained by a defect in nitrogen nutrition due to the reduced peptide transport activity conferred by AtPTR2-B. These results suggest that AtPTRZ-B may play a general role in plant nutrition. l h e AtPTR2-B gene was mapped to chromosome 2, which is closely linked to the restriction fragment length polymorphism marker 111246.

An Arabidopsis Mutant Resistant to Thaxtomin A, a Cellulose Synthesis Inhibitor fromStreptomycesSpecies[W]

“…This finding suggests that the toxin enters plant cells by a carrier-mediated process. It is possible that thaxtomin is sufficiently similar in structure to a dipeptide substrate for one of the hydrophobic dipeptide transporters of Arabidopsis (Song et al, 1996(Song et al, , 1997. The rate of uptake of thaxtomin by the mutant was reduced strongly relative to that of the wild type.…”

Cloning and functional characterisation of a peptide transporter expressed in the scutellum of barley grain during the early stages of germination

“…In contrast, AtPTR2-B was found to be expressed at high levels in several plant tissues, including young leaves, roots and germinating seeds (Song et al, 1996). In situ hybridization revealed AtPTR2-B mRNA to be localized to the embryo within the seedpod (Rentsch et al, 1995), although AtPTR2-B expression was also detected in the stem, flower and mature leaf, indicating that the peptide transporter was constitutively expressed in other plant tissues (Song et al, 1997). Although peptide transport is associated with rapid protein mobilisation especially seed storage protein proteolysis, leaf senescence and seed development, a more general role in the transport of organic nitrogen has been suggested (Higgins and Payne, 1982).…”

“…AtPTR2-A is expressed in A. thaliana roots, and may be responsible for absorption of small amounts of organic nitrogen in the form of peptides from the soil . AtPTR2-B is expressed in most tissues in A. thaliana, but highest expression levels are found in developing embryos where peptide transport may have a role in the supply of nutrients to the immature embryo, although long distance, vascular transport of peptides in plants has yet to be demonstrated (Song et al, 1997). In both cases, peptide concentrations are likely to be low and the transporters are of high affinity.…”

“…AtPTR2-B (NTR1) was first identified in a screen for histidine transporters although histidine transport rates in S. cerevisiae expressing NTR1 were too low to measure (Frommer et al, 1994). AtPTR2-B expression was found in most plant tissues, with particularly high levels in the developing seedpods (Frommer et al, 1994;Rentsch et al, 1995;Song et al, 1996Song et al, , 1997. Transgenic A. thaliana with reduced levels of AtPTR2-B expression showed abnormal seed development, with fewer, larger seeds per silique than wild type plants, consistent with a role for peptide transport in seed development (Song et al, 1997).…”

“…AtPTR2-B expression was found in most plant tissues, with particularly high levels in the developing seedpods (Frommer et al, 1994;Rentsch et al, 1995;Song et al, 1996Song et al, , 1997. Transgenic A. thaliana with reduced levels of AtPTR2-B expression showed abnormal seed development, with fewer, larger seeds per silique than wild type plants, consistent with a role for peptide transport in seed development (Song et al, 1997). Developing barley embryos 21-27 days after anthesis also exhibit peptide transport activity although with µ 200-fold lower affinity for peptides compared to yeast expressing AtPTR2-B (Hardy and Payne, 1992;Sopanen et al, 1985b).…”