Role of miR156-targeted SlySBP15 in axillary bud outgrowth in Solanum lycopersicum

Abstract

The development of axillary branches is essential for shaping shoot architecture, besides being an important determinant of crop yield. Branches are originated from axillary buds formed in the axils of leaves which can remain dormant or outgrow in a new side-shoot, in a process tightly regulated by several signals, such as sugars, phytohormones, transcription factors (TFs) and microRNAs (miRNAs). We have previously showed that plants overexpressing the microRNA156 (156OE) in tomato show increased branching. Meanwhile, members of the SQUAMOSA PROMOTER-BINDING PROTEIN (SPL/SBP) family - targeted by miR156 - have also been described as negative regulators of axillary bud outgrowth. In this project, we have demonstrated that overexpression of a miR156-resistant version of SlySBP15 (rSBP15OE) inhibit axillary bud outgrowth. Apically-derived auxin is the main hormone known to inhibit bud outgrowth in different species. We have demonstrated that 156OE plants show reduced polar auxin transport (PAT) in the stem and diminished auxin response in axillary buds compared to wild-type plants. In this proposal, we intend to investigate whether miR156-targeted SBPs affect PAT by interfering with the expression and/or protein localization of the auxin transporter PIN1. We also plan to investigate the interaction between SlySBP15 and BRANCHED1, a transcription factor known to inhibit bud outgrowth in several species, which integrates several endogenous and exogenous signals regulating bud outgrowth. Finally, we intend to investigate the interaction between miR156-targeted SlySBPs and strigolactones (SLs), a new class of hormones that negatively controls axillary branching. (AU)