Transcriptome and hormones analysis provide insights into elongated fruit somaclonal mutant in ?Akihime? strawberry

Fruit shape is an important agronomic trait. However, the regulatory mechanism of strawberry fruit shape re-mains largely unknown. In this study, we firstly compared cultivated strawberry 'Akihime' with its elongated fruit somaclonal mutant (finger strawberry). The plant height, crown diameter, leaf length and some photo-synthetic indexes were no significant changes between 'Akihime' and finger strawberry, while the fruit shape of them had obvious differences. Histological observation showed that fruit shape changes mainly resulted from the change of cell area, especially cell length, at small green fruit stage of 'Akihime' and finger strawberry. Next, the endogenous hormone contents of small green fruit of 'Akihime' and finger strawberry were investigated by HPLC-MS/MS. We found that the auxin content in the finger strawberry dramatically increased compared with 'Akihime', while the content of gibberellin and brassinosteroids had no significant difference between 'Akihime' and finger strawberry. Finally, small green fruits of 'Akihime' and finger strawberry were used for identifying key genes responsible for the elongated fruit phenotype through RNA-seq. A total of 674 differentially expressed genes (DEGs) were identified, including 248 up-regulated genes and 426 down-regulated genes. GO and KEGG enrichment analysis showed the DEGs were mainly enriched in DNA replication, cell cycle, plant hormone synthesis and signal transduction. Interestingly, auxin-related genes such as FaIAA33, FaSAUR76, FaSAUR34, FaARF and some transcription factors such as FaMYBs, FabHLHs, FaNACs were differentially expressed in 'Aki-hime' and finger strawberry, which may play a crucial role in the formation of elongated fruit mutant phenotype. These results will provide some insights into the regulatory mechanism of strawberry fruit shape and are helpful for appearance quality improvement of strawberry.