Stimulation of Albino Regeneration from Rice Tissue Culture by Proline Under High Osmosis: A Possible Relationship with an Endogenous Transposable Element Os-MuDR

ABSTRACT

Proline stimulates proliferation of callus and somaclonal variation, particularly albino regeneration, in rice tissue culture under high osmosis. Albino regenerants from scutellum-derived callus exhibited various deletion patterns in chloroplast DNA, similar to those reported in anther-derived albino regenerants. Through differential display one PCR product was selected which showed enhanced expression by proline in scutellum-derived callus. Northern blot analysis revealed a 2.6 kb major transcript. A deduced amino acid sequence of a partial cDNA clone (976 b) selected from a cDNA library constructed from proline-treated callus showed 36% homology with a maize protein (MURA) encoded by an autonomous regulatory transposable element MuDR. A rice homologue to maize MuDR (designated as Os-MuDR) was shown to be present as a single copy gene in Japanese rice cultivars. Our results suggest a possible relationship between Os-MuDR and the high frequency of somatic mutations including albino regeneration in rice tissue culture.