Identification and characterization of An-4, a potential quantitative trait locus for awn development in rice

Awn of rice is an important domestication trait closely associated with yield traits. Therefore, the identification of genes for awn development is of great significance for the elucidation of molecular mechanism of awn development and the genetic improvement of yield traits in rice.

In this study, using chromosome segment substitution lines (CSSLs) derived from a long-awned Guangxi common wild rice (GXCWR, Oryza rufipogon Griff.) and a short-awned indica cultivar 9311, we identified An-4, a potential quantitative trait locus (QTL) for awn development. Then, An-4 was fine mapped into a 56-kb region of chromosome 2, which contained four annotated genes. Among these four annotated genes, Os02g0594800 was concluded to be the potential candidate gene for An-4. An-4 exhibited pleiotropic effects on awn development and several yield traits. Scanning electron microscopy (SEM) analysis showed that An-4 significantly promoted awn development at Sp7 and Sp8 stage of spikelet development. Transcriptome analysis suggested that An-4 might influence the development of awn by regulating the expression of genes related to growth, developmental process, channel regulation and extracellular region. By contrast to those of 9311, the expression level of OsRR5 in CSSL128 was significantly down-regulated, whereas the expression levels of OsCKX2 and OsGA2ox5 in CSSL128 were significantly up-regulated. In addition, our study showed that An-4 had additive effects with other genes for awn development, such as An-1, An-2/LABA1 and An-3/GAD1/RAE2.

The identification of An-4 lays a foundation for cloning of An-4 and further elucidation of the molecular mechanism of awn development. Moreover, the identification of favorable allelic variation of An-4 from 9311 will be useful to improve rice yield traits.