Panicle phytomer 1 mutations affect the panicle architecture of rice

Abstract

We have characterized three panicle phytomer 1 (pap1) mutations from the phytomer viewpoint. In pap1 mutants, rachis phytomers were strongly affected involving a severe reduction of rachis internode length and an increase in the number of rachis internodes (number of phytomers), resulting in a large number of primary branches. In addition, bracts were frequently over-developed. By contrast, pap1 differently affected primary branch phytomers resulting in a reduction in both the number and length of internodes. Spikelets were also modified. Rudimentary and empty glumes were frequently elongated. Floral organs were mostly normal. However, a double mutation between pap1 and fon1 markedly increased the number of floral organs compared with the single fon1 mutation, suggesting that PAP1 has a distinct role in the differentiation of floral organs. The functions of PAP1 on panicle architecture are: (1) the negative regulation of the number of phytomers on the rachis but a positive regulation of the number on primary branches, (2) an elongation of internodes, and (3) the negative regulation of bract development.