Mechanism of low glutelin content in the “glu1” mutant The “ glu1 ” is a gamma-ray-induced rice mutant, which lacks an acidic subunit of glutelin, a major seed storage protein. Morita, et al. [34] elucidated that the glu1 harbors a 129.7 kbp deletion involving two highly similar and tandem repeated glutelin genes, GluB5 and GluB4 . The deletion eliminated the entire GluB5 and GluB4 gene except half of the first exon of GluB5 . As a result, the phenotype of the glu1 gene is a complete lack of the acidic subunit of glutelin and acts as a recessive gene for low glutelin content in rice grains (Fig. 9).
Conclusion The above examples illustrate that the position and the size of deletions in the same loci have the capacity to dramatically alter the phenotype of mutants through the process of transcription and translation. The glu1 , which has a large 129.7 kbp deletion, acts as a recessive gene, while the LGC1 , which has 3.5 kbp deletion including probably a terminal signal of the transcript region acts as a dominant gene. Furthermore, the GluB5 and the GluB4 have the same amino acid sequence in their acidic subunit, suggesting that only the mutation involving both GluB5 and GluB4 result in the resultant phenotype. That is the lack of the glutelin acidic subunit deleted in the “glu1” mutant. It probably is very difficult to knock out both loci by chemical treatment or transposon techniques. Sequenced plant genomes exhibited more that 14% of the genes formed tandem array [3, 35]. This finding, however, suggests that Gamma-rays can be an effective mutagen to generate knock-out mutants of both loci and to analyze tandem repeated and functionally redundant genes.