Abstract: 【Objective】The rice floret opening will be driven by that a pair of lodicules lying between the lemma and the stamen base in the floret will expand rapidly when absorbing abundant water and lever away the rigid lemma. However, little is known about the molecular mechanism of the lodicules regulating the time of floret opening. With the development of sequencing technology, a faster and more effective way is provided to study the mechanism of the responses of lodicules to floret opening time at the whole level of cell.【Method】In this study, conventional indica rice germplasm Zhongzao 25 was used as the material and the transcriptomes of lodicules at 12 h and 1 h before floret opening were sequenced using Illumina sequencing technology. First, clean reads were mapped to the reference sequences of indica 9311 and the unique matched reads were obtained; second, the gene expression level was calculated by using RPKM method; Then, false discovery rate≤ 0.001 and the absolute value of Log₂Ratio ≥ 1 were used as the threshold to judge the significance of gene expression differences. Finally, the functions and pathways of differentially expressed genes (DEGs) were annotated by comparing with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) and Universal Protein Knowledgebase (UniProtKB).【Result】The expressed genes from the two transcriptomes of lodicules at 12 h and 1 h before floret opening were 26 369 and 26 157 respectively, and 3 924 differentially expressed genes (DEGs) were screened between the two transcriptomes. 2 623 DEGs were down-regulated and 1 301 DEGs were up-regulated genes. Moreover, change folds of 105 DEGs were more than 100 folds (|log₂Ratio|≥6.7) of lodicules during the two stages before floret opening. Gene ontology enrichment analysis showed that 1 624 DEGs could be mapped as functional molecule, 21.7% DEGs of which had ion-binding activity, 7.5% DEGs of which had oxidoreductase activity and 5.7% DEGs of which had transporter activity. Meanwhile, 1 313 DEGs were involved in biological processes, 15.0% DEGs participated in localization processes, 12.4% DEGs participated in transport process, 4.7% DEGs participated in carbohydrate metabolic process and 4.5% DEGs participated in lipid metabolic process. KEGG pathway enrichment analysis revealed that 2 229 DEGs were involved in 123 different metabolic pathways，which enriched larger numbers of DEGs including biosynthesis of secondary metabolites (339 genes), plant hormone signal transduction (152 genes), nucleotide metabolism (146 genes), and starch and sucrose metabolism (64 genes). The functions of those genes, which were specifically expressed at 1 hour before floret opening and the unique match reads number of which exceeded 30, were mainly concerned in the regulation of physiological processes of cytoskeleton remodeling, membrane stability, energy metabolism, transcription regulation, and signal transduction. Jasmonic acid and analogs have a strong inductive effect on floret opening in rice, 16 DEGs were involved in jasmonic acid biosynthesis pathway and 11 DEGs were involved in jasmonic acid signal transduction pathway, whose expression levels increased significantly as the floret opening time approached.【Conclusion】The transcriptome data of rice lodicules was obtained using RNA sequencing technology. The expression profiling data of DEGs and molecular function of DEGs were also collected. The differential activation or suppression of key DEGs in energy metabolism, carbohydrates metabolism and translocation, cell walls structure modification and hormones metabolism and signaling pathway in lodicules suggested that these DEGs were closely related to water absorption and expansion of lodicules towards the regulating of the floret opening time.

Key words: rice (Oryza sativa L.), lodicule, floret opening time, transcriptome, Illumina sequencing