QTL mapping and transcriptomics reveal complex and conserved regulation of graft union formation

Abstract

Understanding how grafts form has fascinated scientists for over a century, and numerous transcription factors (TFs) involved in wound healing, callus formation, and graft development have been identified in model plants. However, despite the importance of grafting for cultivating many crops, the genetic architecture underlying grafting-related traits remains poorly characterised.

To address this gap, we mapped quantitative trait loci (QTLs) associated with grafting-related traits in grapevine, including callus formation, mechanical strength of the graft union, and post-grafting growth. However, we were unable to detect QTLs associated with grafting success rate itself. To further investigate the genetic basis of grafting, we integrated transcriptome data comparing grafted and intact tissues, which led to the identification of 36 candidate TFs that may regulate grafting-related traits. Many of these were orthologues of genes known to control defence and wounding responses, callus formation, and tissue regeneration in model species.

We also demonstrated that two TFs previously shown to regulate callus formation and grafting in Arabidopsis perform similar functions in grapevine. This was confirmed by silencing their grapevine orthologues using exogenous double-stranded RNAs, which affected grafting-related processes.

Together, these findings highlight both the difficulty of detecting QTLs for highly complex traits such as grafting success rate and the value of breaking these traits down into simpler component traits. The identification of candidate TFs within QTL regions, combined with functional evidence from gene silencing, suggests that key regulators of grafting are conserved across diverse plant species.

Acknowledgements

This work was supported by the projects VitiGraft and NextVitRoot funded by the Plant2Pro® Carnot Institute in the frame of its 2021 and 2019 calls, Plant2Pro® is supported by ANR (agreements #21-CARN-024-01 – 2021 and #19 CARN 002447701 2019 respectively).