Mechanism of auxin and GA crosstalk in diploid strawberry fruit initiation

Abstract

Strawberry, a high value fruit crop, has recently become amenable for genetic studies due to genomic resources and CRISPR/CAS9 tools. Unlike ovary-derived botanical fruits, strawberry is an accessory fruit derived from receptacle, the stem tip subtending floral organs. Although both botanical and accessory fruits initiate development in response to auxin and GA released from seeds, the downstream auxin and GA signaling mechanisms underlying accessory fruit development remain unknown. Using wild strawberry, we performed in depth molecular characterizations of accessory fruit development. We show that auxin signaling proteins FveARF8/FveARF6 are bound and hence inhibited by FveIAA4 and FveRGA1, repressors in auxin and GA signaling pathways. This inhibition is relieved post-fertilization or by the application of GA or auxin. Mutants of FveRGA1 developed parthenocarpic fruit suggesting a conserved function of DELLA proteins in fruit set. Further, FveARF8 was found to repress the expression of a GA receptor gene GID1c to control fruits sensitivity to GA, revealing a novel crosstalk mechanism. We demonstrate that consensus co-expression network provides a powerful tool for non-model species in the selection of interacting genes for functional studies. These findings will facilitate the improvement of strawberry fruit productivity and quality by guiding future production of parthenocarpic fruit. One sentence summaryGenome editing and network analysis are applied to investigating the mechanism of accessory fruit initiation in the wild strawberry, revealing conserved as well as novel crosstalk mechanisms. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Zhongchi Liu (zliu@umd.edu)