Effects of High Nitrogen Supply on the Susceptibility to Coolness at the Young Microspore Stage in Rice (Oryza sativa L.)

Changes in gene expression patterns by high nitrogen (High-N) and High-N plus cooling at the young microspore stage (High-N-cooling) in rice mature anthers were analyzed by semiquantitative RT-PCR with gene specific primers. Gene expression of alpha-expansin 18 (EXPA18) was repressed under High-N-cooling. Beta-expansin 1 (EXPB1), putative aldehyde dehydrogenase (ALDH) and Fructokinase II (FKII) were upregulated under High-N. EXPB1 and FKII were highly expressed under High-N-cooling. Comprehensive examination of gene expression patterns of 26 alpha-expansins (EXPAs) and 16 beta-expansins (EXPBs) showed that all expansins (EXPs) except EXPA12 were expressed in the anthers. Gene expression of EXPs did not change under High-N except EXPA1, EXPB1 and EXPB5 which were upregulated. In total, 18 EXPAs and 6 EXPBs were repressed under High-N-cooling, and among these, EXPA18, EXPA19 and EXPA20 had high similarities in the amino acid sequences, suggesting that these three genes may constitute a distinct functional gene subfamily related to the decrease in the pollen germination ability.