Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

Abstract

ORCID IDs: 0000-0002-9997-490X (Y.K.); 0000-0001-8867-5085 (C.S.).Phosphorus (P) is a crucial nutrient for plant growth, but its availability to roots is limited in soil. Arbuscular mycorrhizal (AM) symbiosis is a promising strategy for improving plant P acquisition. However, P fertilizer reduces fungal colonization (P inhibition) and compromises mycorrhizal P uptake, warranting studies on the mechanistic basis of P inhibition. In this study, early morphological changes in P inhibition were identified in rice (Oryza sativa) using fungal cell wall staining and live-cell imaging of plant membranes that were associated with arbuscule life cycles. Arbuscule density decreased, and aberrant hyphal branching was observed in roots at 5 h after P treatment. Although new arbuscule development was severely inhibited, preformed arbuscules remained intact and longevity remained constant. P inhibition was accelerated in the rice pt11-1 mutant, which lacks P uptake from arbuscule branches, suggesting that mature arbuscules are stabilized by the symbiotic P transporter under high P condition. Moreover, P treatment led to increases in the number of vesicles, in which lipid droplets accumulated and then decreased within a few days. The development of new arbuscules resumed within by 2 d. Our data established that P strongly and temporarily inhibits new arbuscule development, but not intraradical accommodation of AM fungi.

Nutrient Exchange and Regulation in Arbuscular Mycorrhizal Symbiosis

“…The nutritional status of the plant and surrounding environment, as well as Pi delivered through the AM symbiosis, affect AM symbiosis. However, the underlying mechanisms are mostly unknown (Koide and Schreiner, 1992;Breuillin et al, 2010;Hammer et al, 2011;Kiers et al, 2011;Kretzschmar et al, 2012;Yoneyama et al, 2012;Kobae et al, 2016). Transcriptomic analyses revealed that high levels of Pi repressed the expression of genes encoding carotenoid and strigolactone biosynthesis enzymes in plants, suggesting that high levels of Pi directly inhibit spore germination by reducing strigolactone biosynthesis.…”

Partner communication and role of nutrients in the arbuscular mycorrhizal symbiosis

“…In addition to its cell-autonomous influence on arbuscule maintenance, Pi also regulates AM formation in a systemic manner. It has long been known that AM colonization is repressed when plants are grown under high Pi supply (Mosse, 1973;Branscheid et al, 2010;Balzergue et al, 2011;Kobae et al, 2016). In addition, in split-root experiments, in which only one side of the split root system was fertilized with high Pi concentrations, AM formation was suppressed on both sides (Branscheid et al, 2010;Breuillin et al, 2010;Balzergue et al, 2011).…”

Arbuscular mycorrhizal phenotyping: the dos and don'ts

“…As phospholipids potentially contain phosphate and lipids traded between symbionts, alterations in vesicle abundance may reflect major defects in symbiotic nutrient homeostasis. Unlike arbuscules, vesicle formation is stimulated by phosphate treatment in rice (Kobae et al ., ) suggesting them to have complex yet‐to‐be understood roles in the fungal handling of nutritional resources. Vesicles and spores are overlooked structures but they give account of the completion of fungal life cycle which is, in turn, relevant for subsequent recolonization.…”