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Abstract
The SQUAMOUS PROMOTER BINDING PROTEIN-LIKE (SPL) gene family encodes plant-specific transcription factors that regulate diverse physiological processes, including growth, flowering, and stress responses. A total of 32 PaSPL genes were identified and characterized in the genome of Platanus × acerifolia, an ancient hexaploid species widely cultivated as a street tree. The PaSPL genes were classified into nine distinct groups based on their phylogenetic relationship. Gene structure examination revealed considerable variation in intron number and length among groups. Cis-regulatory element analysis indicated that the promoter regions of PaSPLs are enriched with light-responsive elements. Expression profiling across different tissues and developmental stages demonstrated that the PaSPL genes harboring a site targeted by microRNA156 exhibited stage-specific expression patterns, while those in the Groups II, III, V, and IX displayed tissue-specific expression. Notably, several PaSPL genes exhibited dynamic expression during floral transition, implicating their role in flowering regulation. Among them, PaSPL8a, a Group III member, was differentially expressed in flowerless germplasm resources. Functional characterization demonstrated that PaSPL8a overexpression in Arabidopsis thaliana accelerated flowering and upregulated key flowering regulators. These findings provide mechanistic insights into the function of PaSPLs in P. × acerifolia and establish PaSPL8a as a positive regulator of flowering.
Highlights
The SQUAMOUS PROMOTER BINDING PROTEINLIKE(SPL) gene family encodes plant-specific transcription factors characterized by the presence of an SQUAMOSA—promoter-binding protein (SBP)-box domain, a 76-amino-acid sequence (Cardon et al 1999) containing two zinc finger motifs (Zn-1/2) and a C-terminal nuclear localization signal (NLS) (Yamasaki et al.2004; Yang et al 2008)
Identification and analysis of the PaSPL family genes Based on the available P. × acerifolia genome data, 32 PaSPL proteins were identified and characterized using previously reported Arabidopsis SQUAMOUS PROMOTER BINDING PROTEIN-LIKE (SPL) proteins as references (Table 1)
PaSPL8a, which lacks miR156 target sites, directly activates PaFT and PaFTL, suggesting an independent regulatory mechanism distinct from the miR156-mediated age pathway. These findings indicate that PaSPL8a plays a direct role in flowering regulation, with its functional divergence in P. × acerifolia likely arising from gene duplication events
Summary
The SQUAMOUS PROMOTER BINDING PROTEINLIKE(SPL) gene family encodes plant-specific transcription factors characterized by the presence of an SBP-box domain, a 76-amino-acid sequence (Cardon et al 1999) containing two zinc finger motifs (Zn-1/2) and a C-terminal nuclear localization signal (NLS) (Yamasaki et al.2004; Yang et al 2008). Many SPL members are directly targeted by miR156 and serve as key regulators of vegetative phase transition (Rhoades et al 2002; Wang et al 2009). Functional analyses have demonstrated that AtSPL2/10/11 influence leaf morphology, trichome formation, and flowering time (Gao et al 2018; Shikata et al 2009), while AtSPL3/4/5 promotes vegetative phase transition via the age pathway (Jung et al 2016). Among SPL genes lacking miR156 target sites, AtSPL7 is a key regulator of copper homeostasis, orchestrating the transcription of Cu-response elements (CuREs) under copper-deficient conditions (Yamasaki et al 2009; Yan et al 2017). AtSPL8 influences multiple developmental processes, including stamen filament elongation, petal trichome formation, root development, and gynoecium patterning, primarily through modulation of auxin and gibberellin (GA) signaling pathways (Unte et al 2003; Zhang et al 2007)
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