Abstract: [Objective] In order to reveal molecular mechanism of Catalpa bungei male sterility from the gene expression levels, we analyze the regulation of gene expression patterns for C. bungei male sterility by studying its natural mutation male sterile flower buds, in order to understand male sterility of C. bungei and other woody plants. [Method] The transcriptome sequencing was carried out on male sterile and fertile flower buds. We use the method of comparative analysis to deal with the sterile and fertile bud transcript through bioinformatics, and predict and filter genes about C. bungei male sterility. [Result] Transcriptome sequencing produced a total of 27.18 Gb data. Finally, we obtained 86 076 Unigenes after assembling and removing redundant. Then we make use of the seven function databases (NR, NT, GO, COG, KEGG, Swissprot and Interpro) annotating all the Unigenes, a total of 64 600 (75.05%) Unigenes were eventually annotated by any one of the seven databases. Based on the analysis of expression levels of the Unigenes of the experimental group (male sterile flower buds, SL) and control group (male fertile flower buds, FL). Differently expressed genes with different expression levels and high reliability were screened out. In the noise distribution (expression levels differed over 2 times, reliability over 0.8), 6 915 up-regulated genes and 3 504 down-regulated genes were selected from the experimental group. Poisson distribution (expression levels differed over 2 times, incidence of errors under 0.001), in three biological repeats SL-1 vs FL-1, SL-2 vs FL-2, SL-3 vs FL-3 obtained up-regulated genes respectively of 13 979, 13 513 and 13 055 and down-regulated genes respectively of 12 170, 13 807 and 10 411. The GO functional analysis for differently expressed gene showed that the reproduction process, reproduction development process, reproduction system development, reproductive structure development in biological processes were significantly enriched. In molecular function the auxin efflux transmembrane transporter protein activity was significantly enriched. KEGG pathway analysis indicated that differently expressed genes were mapped to 127 different biological pathways. Those significantly enriched pathways mainly contain metabolic pathways, biosynthesis of secondary metabolites, spliceosome, RNA transport and metabolism of glycerophospholipid and starch and sucrose. By comparing differently expressed genes with these genes that are related to male sterility that have been reported, 246 highly homology Unigenes were distinguished. The COG function classification were more focused on RNA processing and modification, cell cycle control, cell division and chromosome partitions, transcription, etc. The differently expressed genes which were highly homology with the male sterility genes were mapped to the pyruvate metabolism, the plant hormone signal transduction pathway. [Conclusion] The formation of the male sterility for C. bungei is involved in multiple processes of reproductive development, pyruvate metabolism pathway, the auxin efflux transmembrane transporter protein activity and brassinosteroid-mediated signal transduction path. Based on the analyses and relevant cytological observations that have been completed, we assume that the male sterility of C. bungei is possibly due to abnormal pyruvate metabolism process, leading to abnormal brassinosteroid synthesis and tapetum dysplasia which further affect the meiosis of microspores. These eventually resulted in the formation of sterile pollen.

Key words: Catalpa bungei, male sterility, transcriptome sequencing, differentially expressed gene