Abstract:

To reveal the composition，structure，and evolutionary process of the Expansin family genes in Luffa cylindrica，as well as their role in fruit enlargement. This study identified 50 Expansin genes from the genome of sponge gourd by bioinformatics technology，which belong to 4 subfamilies[EXPA（18），EXPB（3），EXLA（27）and EXLB（2）]. Among them，the EXLA subfamily underwent 4 pairs of gene tandem duplication and 6 pairs of gene fragment duplication，resulting in a significant increase in the gene quantity in this subfamily. The phylogenetic tree showed that members of the four subfamilies gather in groups and were closely related to cucumbers. Gene structure and motif analysis showed that the exon intron structure and motif types and distributions of the four subfamilies tended to be conserved in evolution，which can serve as important basis for subfamily typing. Promoter element prediction analysis revealed that the Expansin gene promoter contained a large number of light inducible，anaerobic inducible，methyl jasmonate，and abscisic acid elements，with the highest number of light inducible elements predicted only in the EXLA/EXLB subfamily. Based on RNA-seq data，8 Expansin genes were screened，which were significantly positively correlated with fruit transverse and longitudinal diameter development. Among them，four genes LcEXPA8，LcEXPA18，LcEXPA14，and LcEXPA1 have been reported as potential candidate genes for controlling the fruit shape of sponge gourd. RT-qPCR analysis was performed on the other four genes，and LcEXPA15 was significantly overexpressed at 4 DAA（days after anthesis），LcEXPA3，LcEXPA16 and LcEXPA7 were significantly overexpressed at 8-15 DAA. It was known that 2-15 DAA was the fruit enlargement stage in sponge gourd，during which the number of fruit cells increased and single cells significantly expanded and elongated. So it was concluded that the 4 Expansin genes may play an important role in catalyzing cell growth and promoting fruit enlargement. By constructing 8 Expansin genes interaction network，it was suggested that some Expansin genes may interact with ERF，bHLH，TCP，and GATA four transcription factor families. The above 8 Expansin genes could be selected as candidate genes related with fruit enlargement in sponge gourd for further study.

Key words: Luffa cylindrica, Expansin, gene family, fruit enlargement