Leaf senescence is a developmentally regulated degeneration process to mobilize nutrients from senescing leaves to other tissues such as developing leaves and seeds. Leaf yellowing, which reflects degradation of chlorophyll, is a good indicator of senescence. In rice, leaf yellowing predominates in the late ripening period. Early-yellowing mutants are thought to be

impaired in the regulation of senescence and could be a good material to analyze senescence. A mutant line, NM67, which was obtained from cv. 'Nihonmasari' treated with ethylenimine, showed early yellowing phenotype (Iida et al., 1993). Young plants appear almost normal but begin yellowing from the tips of leaves about four weeks before heading. As they grow, the yellowing phenotype becomes severer, but they finally develop fertile panicles. This trait is thought to be conferred by a single recessive mutation, early yellowing 1 (eye1) (Iida et al., 1993). Together with the early yellowing phenotype, NM67 have a mutant phenotype in the seed storage protein profile: low glutelin and high prolamin content. This trait was conferred by a dominant mutation, Low glutelin content 1 (Lgc1)(Iida et al., 1993, Kusaba et al., 2003). Lgc1 is independent from eye1 (Iida et al., 1993) and no low glutelin phenotype was observed in the eye1 line, which was selected from the F₂ progeny between NM67 and Nihonmasari (data not shown).

To determine the map position of EYE1, we analyzed an F₂ population between the eye1 homozygote (japonica) and cv. Kasalath (indica). Initial analysis using 39 eye1 homozygotes revealed that EYE1 was located between the cleaved amplified polymorphism (CAPS) marker R663 and the simple sequence repeat (SSR) maker MRG5266 on chromosome 3 (Fig. 1). For further analysis, a CAPS maker OJ1212C05.2 was newly developed: the polymorphism between Nihonmasari and Kasalath is detected by DNA amplification with a primer set of OJ1212C05.2F1 (5'-ATGATAATGCTGTTGCAAGAAATG-3') and OJ1212C05.2R2 (5'- CTGTCACTTACTGCAGATGCTTC-3'), and digestion with HaeIII. Analysis using this maker and 75 eye1 homozygotes demonstrated that the genetic disitance between EYE1 and OJ1212C05.2 was 0.66 cM. When the SSR maker C60465 was used, no recombinant was found. Thus, EYE1 is located near the centromere of chromosome 3 while Lgc1 is located on the long arm of chromosome 2 (Kusaba et al., 2003).

References

Iida, S., E. Amano and T. Nishio, 1993. A rice (Oryza sativa L.) mutant having a low content of glutelin and a high content of prolamine. Theor. Appl. Genet. 87: 374-378.

Kusaba, M., K. Miyahara, S. Iida, H. Fukuoka, T. Takano, H. Sassa, M. Nishimura and T. Nishio, 2003. Low Glutelin Content 1: a Dominant Mutation that Suppresses the Glutelin Multigene Family via RNA Silencing in Rice. Plant Cell 15: 1455-1467.