The actin gene family of rice (Oryza sativa L.)

Genomic Southern blots of rice (Oryza saliva L.) DNA probed with a mosquito actin gene have indicated that actin is encoded in a small multigene family. Four different rice actin sequences were isolated from a genomic library. Restriction enzyme mapping, cross-hybridization studies and DNA sequence analysis, suggested that these sequences were more highly diverged than the actin genes from multigene families in animals. Computer analysis, comparing the DNA sequence of the coding region of these four rice actin genes to other actin genes including three other plant sequences, was performed. Both direct sequence comparisons at the nucleotide and amino acid levels as well as an analysis determining the degree of replacement substitution between the various sequences, demonstrated that the plant actins are less conserved than the animal actins. Hybridization of the rice actin sequences to gene-specific Drosophila actin probes suggested that some of the plant actin genes and the Drosophila genes may have descended from a common ancestral sequence. The relative positions of the introns for the plant actin genes are conserved unlike in other organisms where the intron positions vary. Hydropathy profiles of the rice actins using the amino acid sequence deduced from the nucleotide sequence, suggested that the proteins are very similar to the animal actins. Most of the amino acids thought to be structurally and functionally important are conserved in the rice actin sequences.;Finally, analysis of the rice genome using the rice actin sequences for restriction fragment length polymorphism (RFLP) studies was initiated. Genomic DNA was isolated from six different rice varieties, singly digested with twelve different restriction enzymes and the genomic blots hybridized to probes from the four rice actin genes. A few polymorphisms were found. The use of RFLPs for the eventual development of a genetic linkage map in rice is discussed.;RNA blot analysis confirmed that the four rice actin sequences are transcribed. 1.7 to 1.8 kb transcripts were found to hybridize to RNA probes from each of the genes. A preliminary study of the expression of the four genes during the course of the plant development was performed.