Early Lotus japonicus root transcriptomic responses to symbiotic and pathogenic fungal exudates.

Marco Giovannetti,Mara Novero,Paola Bonfante,Alfredo Mari

doi:10.3389/fpls.2015.00480

Marco Giovannetti, Mara Novero + Show 2 more

Open Access

https://doi.org/10.3389/fpls.2015.00480

Copy DOI

Abstract

The objective of this study is to evaluate Lotus japonicus transcriptomic responses to arbuscular mycorrhizal (AM) germinated spore exudates (GSEs), responsible for activating nuclear Ca2+ spiking in plant root epidermis. A microarray experiment was performed comparing gene expression in Lotus rootlets treated with GSE or water after 24 and 48 h. The transcriptional pattern of selected genes that resulted to be regulated in the array was further evaluated upon different treatments and timings. In particular, Lotus rootlets were treated with: GSE from the pathogenic fungus Colletotrichum trifolii; short chitin oligomers (COs; acknowledged AM fungal signals) and long COs (as activators of pathogenic responses). This experimental set up has revealed that AM GSE generates a strong transcriptomic response in Lotus roots with an extensive defense-related response after 24 h and a subsequent down-regulation after 48 h. A similar subset of defense-related genes resulted to be up-regulated also upon treatment with C. trifolii GSE, although with an opposite trend. Surprisingly, long COs activated both defense-like and symbiosis-related genes. Among the genes regulated in the microarray, promoter-GUS assay showed that LjMATE1 activates in epidermal cells and root hairs.

Highlights

Since the land conquest about 450 million years ago, plants had to deal and relate with both pathogenic and beneficial organisms
A microarray experiment with RNA coming from Lotus rootlets treated with germinating spore exudates (GSE) allowed us identifying 134 genes differently regulated after 24 h of treatment with GSE and 21 genes after 48 h (Figure 1)
One third of the genes resulted to be linked to defense or redox mechanisms: they showed an up-regulation after 24 h and most of them had a dramatic down-regulation after 48 h (Table 1), probably pointing to a defense-like response of the plant to the arbuscular mycorrhizal (AM) fungal exudates and a subsequent downregulation of that response

Summary

Introduction

Since the land conquest about 450 million years ago, plants had to deal and relate with both pathogenic and beneficial organisms. Plants had to protect themselves from pathogens, evolving strong defense mechanisms to effectively ward them off (Jones and Dangl, 2006). Plants have developed symbiotic relationships based on a fair nutrient exchange (Kiers et al, 2011). Among the beneficial microorganisms capable to form symbiosis with plants, research has mainly been guided by nutritional aspects (Gutjahr and Parniske, 2013) with less focus on immunity and compatibility aspects (Rey and Schornack, 2013). The two most studied symbioses between plants and soil microorganisms are symbiotic nitrogen fixation (Gage, 2004) and arbuscular mycorrhizal (AM; Parniske, 2008). Plant genetics and mutant analyses allowed to characterize several genes required for both root endosymbioses (in primis LjSYMRK/DMI2, LjPOLLUX/DMI1, LjCCaMK/DMI3 in the case of the model legumes Lotus japonicus and Medicago truncatula, respectively), defining a CSSP (Oldroyd, 2013)

Objectives

Methods

Results

Conclusion