Endogenous rGRF4-GIF1 enables high-efficiency transformation and systemic trichome induction without pleiotropic defects in strawberry.

Abstract

Genetic improvement of the strawberry is constrained by low regeneration efficiency and pronounced genotype-dependency. While the combination of microRNA396 and Growth-Regulating Factor (GRF)-GRF-Interacting Factor (GIF) chimeras have emerged as potent morphogenic triggers, previous use of heterologous regulators in diploid strawberry reported severe developmental abnormalities. Here, we developed an endogenous, miR396-resistant morphogenic toolkit (FverGRF4-GIF1) that achieves high-efficiency, genotype-independent transformation across both diploid and octoploid strawberry backgrounds without compromising vegetative vigor. Beyond its role in organogenesis, we show that the rGRF4-GIF1 module acts as a master regulator of epidermal cell fate. Constitutive expression of the endogenous chimera induced a systemic development of dense unicellular trichomes on leaves, sepals, and stolon tissues. Integrative transcriptomic and transient Dual-LUC reporter assays revealed that this developmental shift is driven by an epigenetic relay; rGRF4-GIF1 transactivates the histone acetyltransferase GCN5, which in turn promotes trichome initiation through the indirect activation of GL1. Concurrently, the trichome branching program is actively prevented by a GCN5-facilitated induction of the R3-MYB repressor CPC, bypassing canonical GIS-dependent signaling. Physiologically, this epidermal change shifted the leaf surface to a highly hydrophobic state (increased contact angle) and significantly reduced non-stomatal water loss in young tissues by increasing boundary layer resistance. Our findings establish the miR396-GRF-GIF axis as a central coordinator of strawberry morphogenesis and physical desiccation barriers, offering a robust strategy for enhancing environmental resilience in complex polyploid crops.