Loss-of-function mutations in the rice homeobox gene OSH15 affect the architecture of internodes resulting in dwarf plants

The rice homeobox gene OSH15 (Oryza sativa homeobox) is a member of the kno tted1-type homeobox gene family, We report here on the identification and c haracterization of a loss-of-function mutation in OSH15 from a library of r etrotransposon-tagged lines of rice. Based on the phenotype and map positio n, we have identified three independent deletion alleles of the locus among conventional morphological mutants. All of these recessive mutations, whic h are considered to be null alleles, exhibit defects in internode elongatio n. Introduction of a 14 kbp genomic DNA fragment that includes all exons, i ntrons and 5'- and 3'- flanking sequences of OSH15 complemented the defects in internode elongation, confirming that they were caused by the loss-of-f unction of OSH15, Internodes of the mutants had abnormal-shaped epidermal a nd hypodermal cells and showed an unusual arrangement of small vascular bun dles. These mutations demonstrate a role for OSH15 in the development of ri ce internodes. This is the first evidence that the knotted1-type homeobox g enes have roles other than shoot apical meristem formation and/or maintenan ce in plant development.