Functional conservation of the grapevine candidate gene INNER NO OUTER for ovule development and seed formation

Valentina Di Rienzo,Martina Marini,Ciro Leonardo Pierri,Cinzia Montemurro,Isabella Mascio,Valentina Fanelli,Zahra Imanifard,Charles S Gasser,Diana Bellin,Wilma Sabetta,Debra J Skinner

doi:10.1038/s41438-021-00467-5

Abstract

Seedlessness represents a highly appreciated trait in table grapes. Based on an interesting case of seedless fruit production described in the crop species Annona squamosa, we focused on the Vitis vinifera INNER NO OUTER (INO) gene as a candidate. This gene encodes a transcription factor belonging to the YABBY family involved in the determination of abaxial identity in several organs. In Arabidopsis thaliana, this gene was shown to be essential for the formation and asymmetric growth of the ovule outer integument and its mutation leads to a phenotypic defect of ovules and failure in seed formation. In this study, we identified in silico the V. vinifera orthologue and investigated its phylogenetic relationship to INO genes from other species and its expression in different organs in seeded and seedless varieties. Applying cross-species complementation, we have tested its functionality in the Arabidopsis ino-1 mutant. We show that the V. vinifera INO successfully rescues the ovule outer integument growth and seeds set and also partially complements the outer integument asymmetric growth in the Arabidopsis mutant, differently from orthologues from other species. These data demonstrate that VviINO retains similar activity and protein targets in grapevine as in Arabidopsis. Potential implications for grapevine breeding are discussed.

Highlights

Grapevine (Vitis vinifera L.) is one of the most cultivated and appreciated fruit crop trees in many regions of the world
In silico analysis of predicted protein sequences confirmed the presence of nuclear localization signals, in line with the expected function, as well as the presence of the conserved YABBY domain located from 2nd to 162th aa, including both hallmarks motifs of the family, i.e., the Zinc finger toward N-terminal and the helix–loop–helix YABBY domain toward C-terminal protein portion[14,15,16] (Supplementary Table S2)
While VIGs silencing of the NbINO orthologue in tobacco inhibited the growth of the outer cell layer of the integument, leading to a decrease in both integument extension and ovule curvature, the tomato SlINO coding region was not able to complement the Arabidopsis ino-1 mutant[27]

Summary

Introduction

Grapevine (Vitis vinifera L.) is one of the most cultivated and appreciated fruit crop trees in many regions of the world. An interesting case of seedless fruit production was described in the spontaneous mutant Thai seedless (Ts) of the crop species Annona squamosa (sugar apple), belonging to an early divergent angiosperm clade[12]. The authors demonstrated that failure in seed formation is due to a defect in the ovules which lack the outer of the two normal integuments, phenocopying the Arabidopsis inner no outer (ino-1) mutant[13] They isolated the Annona INO orthologue gene and showed that the mutant was associated with the deletion of the INO locus, revealing the molecular basis of seedlessness in the Ts mutant and providing an interesting candidate with the potential of introducing seedlessness in further crop species

Methods

Results

Conclusion