Biotic Stress/Applied Plant Bio

Abstract

CS-3-6 - The IPD3- and IPD3B- dependent regulation of AM fungal entry is sensitive to phosphate concentration in Medicago truncatula

Sunday, July 15
2:43 PM - 2:45 PM

For the past 400 million years, Arbuscular Mycorrhizal (AM) symbiosis has persisted between 80% of land plants and Glomeromycotina fungi. In this symbiosis, fungi provide plants with phosphorus in exchange for carbon. Nutrient exchange occurs in arbuscules, fungal structures that proliferate in root cortical cells. Plants must undergo a sophisticated signaling exchange to activate genes required for accommodation of AM fungi. One member of this signaling pathway is Lotus japonicus CYCLOPS, a transcription factor required for symbiotic gene activation. Arbuscules cannot form in cyclops mutants; however, in mutants lacking IPD3, the Medicago truncatula homolog of CYCLOPS, arbuscule development still occurs. A recent phylogenomics analysis revealed that M. truncatula has an additional copy of IPD3, named IPD3B. Since the ipd3 mutant phenotype is less severe than cyclops, we hypothesized that IPD3B also contributes to symbiotic gene activation. To test this hypothesis, we generated and evaluated an ipd3/ipd3b double mutant. Under low phosphate conditions, fungal penetration into the epidermis was partially impaired but the fungus could still form arbuscules in cortical cells. However, as the concentration of phosphate was increased, the ipd3/ipd3b mutant phenotype became more severe, resulting in an even further reduced ability for fungi to penetrate the epidermis, fewer infection units, and reduced arbuscule formation. Autoactive versions of IPD3 and IPD3B induced symbiotic gene expression in the absence of a symbiont, including MtVPY, a gene essential for AM epidermal entry and arbuscule development. Conversely, symbiotic gene activation did not occur in ipd3/ipd3b mutants expressing constitutively active DMI3, a calcium calmodulin-dependent kinase that can spontaneously activate symbiotic gene expression in WT plants. These findings suggest that while IPD3 and IPD3B are important for symbiotic gene activation, under phosphate-limiting conditions, AM symbiosis can proceed independently of IPD3, demonstrating a fundamental difference in AM symbiotic regulation between Medicago truncatula and Lotus japonicus


 

Co-Authors

Allyson MacLean – University of Ottawa; Maria Harrison – Boyce Thompson Institute

Penelope Lindsay

PhD Candidate
Boyce Thompson Institute

I'm a PhD student in Maria Harrison's lab with an interest in mycorrhizal symbiosis and developmental biology.

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Send Email for Penelope Lindsay


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CS-3-6 - The IPD3- and IPD3B- dependent regulation of AM fungal entry is sensitive to phosphate concentration in Medicago truncatula



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