PvRbohB negatively regulates Rhizophagus irregularis colonization in Phaseolus vulgaris

Abstract

Plant NADPH oxidases (RBOHs) regulate the early stages of rhizobial infection in Phaseolus vulgaris and affect nodule function in Medicago truncatula. In contrast, the role of RBOHs in the plant-arbuscular mycorrhizal (AM) symbiosis and in the regulation of reactive oxygen species (ROS) production during the establishment of the AM interaction is largely unknown. In this study, we assessed the role of P. vulgaris Rboh (PvRbohB) during the symbiosis with the AM fungus, Rhizophagus irregularis. Our results indicate that the PvRbohB transcript is significantly up-regulated in the mycorrhized roots of P. vulgaris. Further, the PvRbohB promoter was found to be active during the invasion of R. irregularis. Down-regulation of PvRbohB transcription by RNAi (RNA interference) silencing resulted in diminished ROS levels in the transgenic mycorrhized roots and induced early hyphal root colonization. Interestingly, the size of appressoria increased in PvRbohB-RNAi roots (760 ± 70.1 µm) relative to controls (251 ± 73.2 µm). Finally, the overall level of mycorrhizal colonization significantly increased in PvRbohB-RNAi roots [48.1 ± 3.3% root length colonization (RLC)] compared with controls (29.4 ± 1.9% RLC). We propose that PvRbohB negatively regulates AM colonization in P. vulgaris.

An Autophagy-Related Kinase Is Essential for the Symbiotic Relationship between Phaseolus vulgaris and Both Rhizobia and Arbuscular Mycorrhizal Fungi

“…Uninoculated plants grown under identical conditions were used as controls. Fungal colonization was confirmed by Trypan blue staining and monitored by RT-qPCR measurement of P. vulgaris phosphate-transporter T4 (PvPT-4) transcripts, an indicator of progressive colonization (McGonigle et al, 1990;Arthikala et al, 2013). As expected, the relative levels (G) Fewer nodules were produced by transgenic roots expressing YPF-2xFYVE than by control transgenic roots (expressing YFP).…”

“…Although the AM symbiosis in P. vulgaris has not been characterized in the same level of detail as in M. truncatula ), a previous report described the key stages of AM infection in P. vulgaris roots (Arthikala et al, 2013). To survey the spatiotemporal Pv-PI3K promoter activity upon R. irregularis inoculation of transgenic roots harboring the construct PvPI3K pro :GFP-GUS, we harvested the roots at 3 wai.…”

“…To survey the spatiotemporal Pv-PI3K promoter activity upon R. irregularis inoculation of transgenic roots harboring the construct PvPI3K pro :GFP-GUS, we harvested the roots at 3 wai. R. irregularis was stained with an Alexa Fluor 633 conjugated to wheat germ agglutinin (WGA), which exhibits far-red fluorescence (Arthikala et al, 2013). Pv-PI3K promoter activity, revealed as GFP fluorescence, was restricted to epidermal cells ( Figure 7D) neighboring the contact point of the fungal hyphae ( Figures 7C and 7E, merge) and to those beneath the expanding extraradical hyphae ( Figures 7F to 7H, merge).…”

RbohB, a Phaseolus vulgaris NADPH oxidase gene, enhances symbiosome number, bacteroid size, and nitrogen fixation in nodules and impairs mycorrhizal colonization

“…As in the rhizobial symbiosis, ROS play a key role during the plant–AMF interaction. The accumulation of H 2 O 2 at the appressorium and in cells containing arbuscules illustrates the spatial and temporal nature of ROS production in legumes inoculated with Rhizophagus irregularis (formerly Glomus intraradices ; Salzer et al ., ; Arthikala et al ., ). Silencing of genes involved in ROS production, such as ROP9 , the small GTPase from M. truncatula (Kiirika et al ., ), or P. vulgaris RbohB (Arthikala et al ., ), induced early hyphal colonization and enhanced root length colonization of transgenic roots in a ROS‐dependent manner.…”

Abscisic Acid and LATERAL ROOT ORGAN DEFECTIVE/NUMEROUS INFECTIONS AND POLYPHENOLICS Modulate Root Elongation via Reactive Oxygen Species in Medicago truncatula

“…In Arabidopsis, AtRbohC/ROOT HAIR DEFECTIVE2 is required for root hair tip growth (Foreman et al, 2003;Takeda et al, 2008) and AtRbohF is required for Casparian strip formation (Lee et al, 2013) and functions with AtRbohD to regulate root length in response to ABA (Kwak et al, 2003). In Phaseolus vulgaris, PvRbohB promotes lateral root elongation (Montiel et al, 2012 and the formation of symbiotic root nodules (Montiel et al, 2012;Arthikala et al, 2013). In M. truncatula, MtRbohA promotes nitrogen fixation in root nodules, but whether it functions in root growth has not been explored (Marino et al, 2011), and no other MtRboh genes have been functionally characterized.…”