PpSPL1 and PpSPL15 inhibit peach branching by increasing strigolactone synthesis.

PpSPL1 and PpSPL15 inhibit peach branching by directly binding to and upregulating the expression of strigolactone (SL) synthesis gene PpLBO1. Branch number is a crucial agronomic trait that influences tree architecture, directly affecting fruit yield and quality. It remains unknown whether SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL), an important transcription factor in determining plant architecture, is involved in the peach branching process. In this study, we found that PpSPL1 and PpSPL15 exhibited significantly higher expression levels in pillar type peach 'Sahonglongzhu' (with fewer secondary branches) compared to standard-type peach 'Okubo' (with more secondary branches). PpSPL1 and PpSPL15 can directly bind to the promoter of the SL synthesis gene PpLBO1. Transient overexpression of PpSPL1 and PpSPL15 in 'Sahonglongzhu' peach axillary buds significantly increased the expression of PpLBO1 and endogenous SL content. Conversely, opposite results were obtained when the expression of PpSPL1 and PpSPL15 was transiently silenced in peach axillary buds. Gene function analysis indicated that transient overexpression of PpSPL1 and PpSPL15 in peach seedlings clearly inhibited peach branching. On the contrary, the number of branches dramatically increased when the expression of PpSPL1 and PpSPL15 were transiently silenced in peach seedlings. These results suggested that PpSPL1 and PpSPL15 could bind to and enhance the expression of PpLBO1, further inhibiting peach branching.