Identification and functional characterization of floral transition-related SPL genes in Pleioblastus pygmaeus

Floral transition has consistently remained a focal point in bamboo plants due to their unique reproductive characteristics. SPL (SQUAMOSA promoter binding protein-like) gene family encodes a class of plant-specific transcription factors (TFs) that fulfill diverse biological functions throughout the plant life, with particular prominence in phase transition. However, their functional roles and regulatory modes remain poorly understood in bamboo plants, as previous work has been confined to transcriptomic profiling and phylogenetic analyses without experimental corroboration. In this study, we identified six SPL candidates potentially involved in floral transition and flower organ development from an ornamental ground-cover bamboo species, Pleioblastus pygmaeus. Notably, four of these, namely PpSPL12, PpSPL13, PpSPL14 and PpSPL16, have been experimentally validated as direct targets of miR156a in our previous work. Tissue-specific expression profiling revealed distinct spatial patterns among the six PpSPLs, which were predominantly expressed in the different developmental stages of flowering P. pygmaeus. The transgenic rice overexpressing each of the six PpSPLs consistently exhibited delayed heading dates. Moreover, overexpression of the four miRNA156-targeted PpSPLs significantly altered vegetative growth of transgenic rice, manifested as decreased plant height and fewer tillers. Similarly, the transgenic Arabidopsis overexpressing the four miR156-targeted PpSPLs exhibited significantly delayed bolting and reduced rosette leaf numbers. Furthermore, several key flowering-promoting genes were quantified to be significantly repressed, whereas a few flowering inhibitory genes were substantially induced in these transgenic plants. In conclusion, results from heterologous overexpression of miR156-targeted PpSPLs in the model plants reveal their functional potential and divergence in both reproductive and vegetative growth, which provides theoretical basis for enriching and deepening bamboo developmental biology.