Gibberellins interfere with symbiosis signaling and gene expression and alter colonization by arbuscular mycorrhizal fungi in Lotus japonicus.

Abstract

Arbuscular mycorrhiza is a mutualistic plant-fungus interaction that confers great advantages for plant growth. Arbuscular mycorrhizal (AM) fungi enter the host root and form symbiotic structures that facilitate nutrient supplies between the symbionts. The gibberellins (GAs) are phytohormones known to inhibit AM fungal infection. However, our transcriptome analysis and phytohormone quantification revealed GA accumulation in the roots of Lotus japonicus infected with AM fungi, suggesting that de novo GA synthesis plays a role in arbuscular mycorrhiza development. We found pleiotropic effects of GAs on the AM fungal infection. In particular, the morphology of AM fungal colonization was drastically altered by the status of GA signaling in the host root. Exogenous GA treatment inhibited AM hyphal entry into the host root and suppressed the expression of Reduced Arbuscular Mycorrhization1 (RAM1) and RAM2 homologs that function in hyphal entry and arbuscule formation. On the other hand, inhibition of GA biosynthesis or suppression of GA signaling also affected arbuscular mycorrhiza development in the host root. Low-GA conditions suppressed arbuscular mycorrhiza-induced subtilisin-like serine protease1 (SbtM1) expression that is required for AM fungal colonization and reduced hyphal branching in the host root. The reduced hyphal branching and SbtM1 expression caused by the inhibition of GA biosynthesis were recovered by GA treatment, supporting the theory that insufficient GA signaling causes the inhibitory effects on arbuscular mycorrhiza development. Most studies have focused on the negative role of GA signaling, whereas our study demonstrates that GA signaling also positively interacts with symbiotic responses and promotes AM colonization of the host root.

• Authors: Naoya Takeda, Yoshihiro Handa, Syusaku Tsuzuki, Mikiko Kojima, Hitoshi Sakakibara, Masayoshi Kawaguchi
• Journal: Plant physiology (Plant Physiol) Vol. 167 Issue 2 Pg. 545-57 (Feb 2015) ISSN: 1532-2548 [Electronic] United States
• PMID: 25527715 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 American Society of Plant Biologists. All Rights Reserved.

Chemical References

• Gibberellins
• Plant Growth Regulators

Topics

• Biosynthetic Pathways (genetics)
• Colony Count, Microbial
• Gene Expression Regulation, Plant (drug effects)
• Genes, Plant
• Gibberellins (biosynthesis, metabolism, pharmacology)
• Glomeromycota (drug effects, growth & development, physiology)
• Hyphae (drug effects)
• Lotus (drug effects, genetics, microbiology)
• Models, Biological
• Mycorrhizae (drug effects, growth & development, physiology)
• Organ Specificity (genetics)
• Plant Growth Regulators (metabolism)
• Plant Roots (genetics, microbiology)
• Signal Transduction (drug effects, genetics)
• Symbiosis (drug effects, genetics)
• Up-Regulation (genetics)