A Medicago truncatula SWEET transporter implicated in arbuscule maintenance during arbuscular mycorrhizal symbiosis

Jianyong An, Tian Zeng, Chuanya Ji, Sanne de Graaf, Zijun Zheng, Ting Ting Xiao, Xiuxin Deng, Shunyuan Xiao, Ton Bisseling, Erik Limpens*, Zhiyong Pan

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

15 Citations (Scopus)

Abstract

Plants form a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi, which facilitates the acquisition of scarce minerals from the soil. In return, the host plants provide sugars and lipids to its fungal partner. However, the mechanism by which the AM fungi obtain sugars from the plant has remained elusive. In this study we investigated the role of potential SWEET family sugar exporters in AM symbiosis in Medicago truncatula. We show that M. truncatula SWEET1b transporter is strongly upregulated in arbuscule-containing cells compared to roots and localizes to the peri-arbuscular membrane, across which nutrient exchange takes place. Heterologous expression of MtSWEET1b in a yeast hexose transport mutant showed that it mainly transports glucose. Overexpression of MtSWEET1b in M. truncatula roots promoted the growth of intraradical mycelium during AM symbiosis. Surprisingly, two independent Mtsweet1b mutants, which are predicted to produce truncated protein variants impaired in glucose transport, exhibited no significant defects in AM symbiosis. However, arbuscule-specific overexpression of MtSWEET1bY57A/G58D, which are considered to act in a dominant-negative manner, resulted in enhanced collapse of arbuscules. Taken together, our results reveal a (redundant) role for MtSWEET1b in the transport of glucose across the peri-arbuscular membrane to maintain arbuscules for a healthy mutually beneficial symbiosis.

Original languageEnglish
Pages (from-to)396-408
JournalNew Phytologist
Volume224
Issue number1
Early online date31 May 2019
DOIs
Publication statusPublished - Oct 2019

Keywords

  • arbuscular mycorrhiza (AM)
  • glucose
  • Medicago truncatula
  • sugar export
  • SWEET
  • symbiosis

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