Biological and Transcriptomic Characterization of Pre-Haustorial Resistance to Sunflower Broomrape (Orobanche cumana W.) in Sunflowers (Helianthus annuus).

Dana Sisou,Yaakov Tadmor,Dina Plakhine,Hammam Ziadna,Hanan Eizenberg,Sariel Hübner

doi:10.3390/plants10091810

Abstract

Infestations with sunflower broomrape (Orobanche cumana Wallr.), an obligatory root parasite, constitute a major limitation to sunflower production in many regions around the world. Breeding for resistance is the most effective approach to reduce sunflower broomrape infestation, yet resistance mechanisms are often broken by new races of the pathogen. Elucidating the mechanisms controlling resistance to broomrape at the molecular level is, thus, a desirable way to obtain long-lasting resistance. In this study, we investigated broomrape resistance in a confectionery sunflower cultivar with a robust and long-lasting resistance to sunflower broomrape. Visual screening and histological examination of sunflower roots revealed that penetration of the broomrape haustorium into the sunflower roots was blocked at the cortex, indicating a pre-haustorial mechanism of resistance. A comparative RNA sequencing between broomrape-resistant and -susceptible accessions allowed the identification of genes that were significantly differentially expressed upon broomrape infestation. Among these genes were β-1,3-endoglucanase, β-glucanase, and ethylene-responsive transcription factor 4 (ERF4). These genes were previously reported to be pathogenesis-related in other plant species. This transcriptomic investigation, together with the histological examinations, led us to conclude that the resistance mechanism involves the identification of the broomrape and the consequent formation of a physical barrier that prevents the establishment of the broomrape into the sunflower roots.

Highlights

Among the plethora of plant pathogens, parasitic weeds are considered a major threat to crops worldwide
We examined the resistance of the confectionery hybrid cultivar ‘EMEK3’, which has high, long-term resistance to sunflower broomrape, with the aim to elucidate—biologically and transcriptomically—the broomrape resistance mechanism, an essential step toward the development of effective sunflower breeding programs
All plants with a susceptible root or rootstalk were infested with 420–450 O. cumana tubercles and stalks of different sizes, regardless of whether the grafted scions were resistant or susceptible (Figure 1a,b)

Summary

Introduction

Among the plethora of plant pathogens, parasitic weeds are considered a major threat to crops worldwide. The second resistance mechanism—known as post-attachment or pre-haustorial resistance [4]—is a mechanism inhibiting penetration into the host root cells as well as the development of the haustorium, preventing vascular conductivity between the parasite and the host [8]. Louarn et al (2016) [28] studied resistance to races F and G and identified a total of 17 QTLs in accordance with different stages of broomrape development. These results were further supported by Imerovski et al (2019) [29]. We examined the resistance of the confectionery hybrid cultivar ‘EMEK3’ (developed by Sha'ar Ha'amakim Seeds, Ltd.), which has high, long-term resistance to sunflower broomrape, with the aim to elucidate—biologically and transcriptomically—the broomrape resistance mechanism, an essential step toward the development of effective sunflower breeding programs

Methods

Results

Conclusion