Identification and expression analysis of PIN genes in rice

We identified 12 PIN genes in rice which encode efflux carrier proteins of phytohormone auxin. Phytogenetic analysis showed that 11 genes were categorized into branches with Arabidopsis PIN genes and one had no close homologue in Arabidopsis. RT-PCR analysis showed expression of 10 PIN genes in various organs depending on genes. No expression of OsPIN3b was detected in the organs examined. OsPIN1b and OsPIN1d were very similar both in sequence and in expression pattern, and in the shoot apex, OsPIN1b/1d was expressed in regions where vascular tissues were developing in young leaf. OsPIN2, OsPIN3a and OsPIN5a were expressed in the entire shoot apex with slight preference in an outermost cell layer. These results indicate that rice has several distinct members of the PIN genes which have various expression patterns, and suggest that polar auxin transport is mediated by different combinations of the PIN genes in each organ in rice.