Different Responses of Two Genes Associated with Disease Resistance Loci in Maize (Zea maysL.) to 3-allyloxy-1,2-benzothiazole 1,1-dioxide

Abstract

Probenazole (3-allyloxy-1,2-benzothiazole 1,1-dioxide, PBZ) is a bactericide and fungicide that acts by inducing plant defense systems. It has been shown to induce the expression of NBS-LRR genes like RPR1 (rice probenazole-response gene) in rice (Oryza sativa L.) and systemic acquired resistance (SAR)-like disease resistance. Two maize (Zea mays L.) genes Zmnbslrr1 (a NBS-LRR gene, cloned from a disease resistance analog PIC11 based) and Zmgc1, (a putative guanylyl cyclaselike gene) have both been associated with quantitative resistance loci (QTL) for resistance to Fusarium graminearum. PIC11 was associated with Fusarium stalk rot and ZmGC1 showed resistance to Gibberella ear rot caused by F. graminearum. The objectives of the current study here were to characterize the Zmnbslrr1 gene and to determine whether it and Zmgc1 respond to the inducer PBZ. The transcript abundance of Zmnbslrr1 expression was significantly reduced in corn seedlings of the Gibberella ear rot resistant genotype CO387 48 h after PBZ treatment. In contrast, the transcript abundance of the maize Zmgc1 gene increased more than 10-fold 8h after the treatment. Therefore, the two genes do not appear to be coordinately regulated by PBZ.Keywords: maize, Zmnbslrr1, Zmgc1, probenazole IntroductionPlants utilize chemical barriers, consisting of antimicrobial compounds, physical barriers such as reinforced cell walls, and sensing barriers, including arrays of resistance (R) genes, to prevent pathogen infection (Dangl and Jones, 2001). Pathogen infestation can cause accumulations or reductions in transcript levels (Iqbal et al., 2005). Plant disease resistance and response genes can be classified into many distinct groups based on the characteristics of the proteins that they encode and the regulons that control their expression. The largest group of such genes encodes proteins with a nucleotide binding site (NBS) motif in the amino-terminal domain followed by a variable number of leucine rich repeats (LRRs) domain in carboxyterminal domain (Meyers et al., 2003;Belkhadir et al., 2004). The NBS domain may function in ATP hydrolysis and signal transduction while the LRR is hypothesized to be responsible for recognizing a pathogen derived signal (Belkhadir et al., 2004). NBS-LRR genes are wide-spread in plants and may also be involved in plant development and responses to abiotic stresses (Michelmore, 2000).In some situations, a single resistance gene might provide protection against one or more strains of a particular pathogen when introduced into a susceptible plant of the same species. However, many disease resistance genes recognize only very limited number of pathogen isolates and therefore, they are the quickly defeated by co-evolving pathogens (Pink, 2002). The evolutionary tug of war, often called the "Red Queen Hypothesis" assumes that plant pathogens will constantly evolve to overcome plant defense barriers (Clay and Kover, 1996).For a more sustainable plant pathogen management system, partial resistance combined with chemical control m...