Abstract:

【Objective】 The SQUAMOSA promoter binding protein like（SPL）transcription factor is a crucial regulatory element in the induction of plant flowering. This study aims to identify the members of the SPL（JrSPL）gene family within the walnut genome and analyze their expression characteristics. The findings of this study will serve as a valuable reference for further investigations into the functional aspects of SPL in walnut flowering induction. 【Method】 The present study employed bioinformatics techniques to identify members of the JrSPL gene family, subsequently to predict their fundamental physicochemical properties, conserved domains, evolutionary relationships, and cis acting elements of promoters. Additionally, transcriptome sequencing and RT-qPCR technology were employed to investigate the expressions of JrSPL family members in various tissues of walnut, as well as following grafting-induced flowering. 【Result】 The JrSPL family consisted of 28 members, showing significant conservation in their gene and protein structures, which were dispersed across 14 distinct chromosomes within the walnut genome. Notably, there were 17 collinear relationships with Arabidopsis and 24 with Populus tomentosa, respectively. Through phylogenetic analysis, these members were categorized into 8 distinct groups. Additionally, the JrSPL promoter region encompassed a substantial quantity of light responsive elements, hormone responsive elements, stress responsive elements, and other similar regulatory motifs. The transcriptome analysis revealed that the JrSPL genes demonstrated varying expressions across different tissues of walnut, including male flowers, female flowers, apical buds, and leaves. Notably, the expressions of most genes were relatively high in female flowers, with 6 genes having significant expression, suggesting their potential involvement in the induction of flowering. In the context of grafting-induced walnut flowering materials, with the except of JrSPL8, the expressions of 12 JrSPLs observed in the flowering materials were found to be greater than those in the control group. Specifically, JrSPL2 and JrSPL25 showed significant expressions in the male flowers of mixed inflorescences, whereas JrSPL8 had high expression in the apical buds. 【Conclusion】 The JrSPL gene exerts a significant influence on the process of walnut flowering, with its high expression serving as the primary determinant of early flowering.

Key words: Juglans regia, SPL gene, genome-wide identification, tissue-specific expression, flowering induction