The WRKY45-Dependent Signaling Pathway Is Required For Resistance against Striga hermonthica Parasitism

Abstract

The root hemiparasite witchweed (Striga spp.) is a devastating agricultural pest that causes losses of up to $1 billion US annually in sub-Saharan Africa. Development of resistant crops is one of the cost-effective ways to address this problem. However, the molecular mechanisms underlying resistance are not well understood. To understand molecular events upon Striga spp. infection, we conducted genome-scale RNA sequencing expression analysis using Striga hermonthica-infected rice (Oryza sativa) roots. We found that transcripts grouped under the Gene Ontology term defense response were significantly enriched in upregulated differentially expressed genes. In particular, we found that both jasmonic acid (JA) and salicylic acid (SA) pathways were induced, but the induction of the JA pathway preceded that of the SA pathway. Foliar application of JA resulted in higher resistance. The hebiba mutant plants, which lack the JA biosynthesis gene ALLENE OXIDE CYCLASE, exhibited severe S. hermonthica susceptibility. The resistant phenotype was recovered by application of JA. By contrast, the SA-deficient NahG rice plants were resistant against S. hermonthica, indicating that endogenous SA is not required for resistance. However, knocking down WRKY45, a regulator of the SA/benzothiadiazole pathway, resulted in enhanced susceptibility. Interestingly, NahG plants induced the JA pathway, which was down-regulated in WRKY45-knockdown plants, linking the resistant and susceptible phenotypes to the JA pathway. Consistently, the susceptibility phenotype in the WRKY45-knockdown plants was recovered by foliar JA application. These results point to a model in which WRKY45 modulates a cross talk in resistance against S. hermonthica by positively regulating both SA/benzothiadiazole and JA pathways.

Expression of molecular markers associated to defense signaling pathways and strigolactone biosynthesis during the early interaction tomato-Phelipanche ramosa

“…An activation of the JA pathway has also been observed in the interaction of rice and sorghum with the hemiparasite Striga hermonthica [52e54]. Moreover, in the case of rice, Mutuku and co-workers have recently shown that the JA-deficient mutant hebiba was more susceptible to S. hermonthica than the corresponding wild-type and that the resistant phenotype was recovered by JA application [53]. Altogether, the data indicate an involvement of the JA signaling pathway in the defense response of the host at the initial stages of host-parasitic plant interactions, as it happens in other plantpathogen interactions such as fungi and bacteria.…”

Haustorial Hairs Are Specialized Root Hairs That Support Parasitism in the Facultative Parasitic Plant Phtheirospermum japonicum

“…Striga spp. plants are major threats to world food security because they parasitize important crops, including maize (Zea mays), sorghum (Sorghum bicolor), rice (Oryza sativa), cowpea (Vigna unguiculata), and sugarcane (Saccharum officinarum), and cause severe yield reductions (Aly, 2007;Scholes and Press, 2008;Mutuku et al, 2015). In particular, in sub-Saharan Africa and Asia, Striga spp.…”

Molecular Parasitic Plant–Host Interactions

“…Various defence responses have been observed, such as induction of immunity-related genes, ROS production, deposition of callose and other phenolic compounds, and vessel occlusion, as well as localized hypersensitive response (HR), which often leads to the arrest of the invasion followed by the necrosis of the parasitic structures [26–28]. The nature and timing of the defence responses together with the molecular components involved suggest the implication of the multilayered plant innate immune system originally described to function against microorganisms [29].…”