Poly(A) tail shortening of alpha-amylase mRNAs in vegetative tissues of Oryza sativa.

The pattern of expression for the entire alpha-amylase gene family in rice vegetative tissues during the developmental growth stages has been studied. We were surprised that the size of rice alpha-amylase mRNAs in the young roots, shoots, and different tissues from adult plant was shorter by approximately 250 bases than that in immature or mature embryos and aleurone layers of seed. Interestingly, the difference in the size of the alpha-amylase mRNAs of rice seed and vegetative tissues is due to the variation in the length of the 3'-poly(A) tracts. In addition, if without glycogen-precipitated treatment for alpha-amylase purification, no alpha-amylases can be detected in vegetative tissues by Western blot analysis. Furthermore, in vitro translation assay revealed that alpha-amylase mRNAs receiving shortened poly(A) tracts in vegetative tissues become translationally repressed. These results indicate that the 3'-poly(A) tract of eukaryotic mRNAs plays an important role in controlling mRNA translatability.