Background
Symbiotic interactions shape an individual’s physiology; no organism "is an island, entire of itself".
Mycorrhizal symbioses are mutualisms between soil fungi and 80% of land plants, including most crop species. Mycorrhizal fungi shape plant development by improving root access to soil nutrients, particularly when these resources are scarce. In exchange, plants provide mycorrhizal fungi with carbohydrates. Two types of mycorrhizal associations are the primary focus of current ecological and physiological research: arbuscular mycorrhizae (AM) and ectomycorrhizae (ECM). ECM are generally restricted to woody plants, especially trees, whereas AM associate with a greater diversity of species. Our research focuses on harnessing mycorrhizal symbioses to offer an efficient alternative to the use of chemical fertilizers, through the understanding of nutrient allocation mechanisms.
Our publications on the mycorrhizal transportome and nutrient exchanges:
Ruytinx J., Kafle A., Usmam M., Coninx L., Zimmermann S.D., Garcia K. (2020) Micronutrient transport in mycorrhizal symbiosis; zinc steals the show. Fungal Biology Reviews. 34(1): 1-9.
Becquer A., Guerrero-Galán C., Eibensteiner J.L., Houdinet G., Bücking H., Zimmermann S.D., Garcia K. (2019) The ectomycorrhizal contribution to tree nutrition. In "Molecular physiology and biotechnology of trees". Francisco Cánovas (ed). Advances in Botanical Research, Volume 89. (In press).
Guerrero-Galán C., Houdinet G., Calvo-Polanco M., Bonaldi K.E., Garcia K., Zimmermann S.D. (2018) The role of plant transporters in mycorrhizal symbioses. In "Membrane transport in plants". Christophe Maurel (ed). Advances in Botanical Research, Volume 87: 303-342.
Garcia K., Doidy J., Zimmermann S.D., Wipf D., Courty P.E. (2016) Take a trip through the plant and fungal transportome of mycorrhiza. Trends in Plant Science. 21: 937-950.
Courty P.E., Doidy J., Garcia K., Wipf D., Zimmermann S.D. The transportome of mycorrhizal systems. In “Molecular Mycorrhizal Symbiosis”. Francis Martin (ed). Wiley-Blackwell (Publisher). ISBN: 978-1-118-95141-5.
Garcia K., Delaux P.M., Cope K.R, Ané J.M. (2015) Molecular signals required for the establishment and maintenance of ectomycorrhizal symbioses. New Phytologist. 208(1): 79-87.
Casieri L., Ait Lahmidi N., Doidy J., Fourrey C., Migeon A., Bonneau L., Courty P.E., Garcia K., Charbonnier M., Delteil A., Brun A., Zimmermann S., Plassard C., Wipf D. (2013) Biotrophic transportome in mutualistic plant-fungal interactions. Mycorrhiza. 23(8): 597-625.
The role of arbuscular mycorrhizal symbiosis in plant potassium (K+) nutrition
The dependence on fertilizers is becoming a critical issue in complex agroecosystems. In the USA, a high proportion of soil samples tested are below the critical level for K+, resulting in the annual use of a large amount of fertilizers by growers. For example, 68% of soil samples tested in North Carolina in 2015 were in K+ deficiency. Moreover, the cost of chemical K+ inputs has multiplied by ten and their use has multiplied by fourteen in the past fifty years (http://www.ers.usda.gov/), making the identification of alternative biological K+ sources an urgent need for modern agriculture practices.
Our work is revealing the importance of mycorrhizal fungi in plant K+ nutrition. Using isotopic, biochemical and transcriptomic approaches, we assess the responses of mycorrhizal roots from model and crop plants to limiting K+ conditions, in field, greenhouse and laboratory conditions.
Our publications on K+ transport in arbuscular mycorrhizal symbiosis:
Garcia K., Ané, J.M. (2017) Polymorphic responses of Medicago truncatula accessions to potassium deprivation. Plant Signaling & Behavior. 12(4): e1307494.
Garcia K., Chasman D., Roy S., Ané J.M. (2017) Physiological responses and gene co-expression network of mycorrhizal roots under K+ deprivation. Plant Physiology. 173: 1811-1823.
Garcia K., Zimmermann S. (2014) The role of mycorrhizal associations to plant potassium nutrition. Frontiers in Plant Science. 5: 337.
Characterization of K+ transport proteins in ectomycorrhizal fungi
We analyze potassium transporters and channels in the ectomycorrhizal fungus Hebeloma cylindrosporum. We identified two families of transporters potentially involved in potassium acquisition, Trk (transporter of K+) and HAK (high-affinity K+ uptake); and two families of channels possibly involved in K release towards the host plant, TOK (tandem-pore outward K+ channel) and SKC (shaker-like K+ channel). In close collaboration with Dr. Sabine Zimmermann in France (CNRS, Montpellier), we study the expression, regulation, and role of these candidates in ectomycorrhizal association.
Our publications on K+ transport in ectomycorrhizal symbiosis:
Garcia K., Guerrero-Galán C., Frank H.E.R., Haider M.Z., Delteil A., Conéjéro G., Lambilliotte R., Fizames C., Sentenac H., Zimmermann S.D. (2020) Fungal Shaker-like channels beyond cellular K+ homeostasis: a role in ectomycorrhizal symbiosis between Hebeloma cylindrosporum and Pinus pinaster. PLOS ONE. 15(11): e0242739.
Guerrero-Galán C., Garcia K., Houdinet G., Zimmermann S.D. (2018) HcTOK1 participates in the maintenance of K+ homeostasis in the ectomycorrhizal fungus Hebeloma cylindrosporum, which is essential for the symbiotic K+ nutrition of Pinus pinaster. Plant Signaling & Behavior. 13(6): e1480845.
Guerrero-Galán C., Delteil A., Garcia K., Houdinet G., Sentenac H., Zimmermann S.D. (2018) Plant potassium nutrition in ectomycorrhizal symbiosis: properties and roles of the three fungal TOK potassium channels in Hebeloma cylindrosporum. Environmental Microbiology. 20: 1873-1887.
Garcia K., Zimmermann S. (2014) The role of mycorrhizal associations to plant potassium nutrition. Frontiers in Plant Science. 5: 337.
Garcia K., Delteil A., Conejero G., Becquer A., Plassard C., Sentenac H., Zimmermann S. (2014) Potassium nutrition of ectomycorrhizal Pinus pinaster: overexpression of the Hebeloma cylindrosporum HcTrk1 transporter affects the translocation of both K(+) and phosphorus in the host plant. New Phytologist. 201(3): 951-960.
Phosphorus transport and homeostasis in the ectomycorrhizal fungus Hebeloma 
cylindrosporum
In close collaboration with Dr. Claude Plassard in France (INRA, Montpellier), we identified, described, and characterized three fungal transporters (H+:Pi) involved in inorganic phosphate acquisition from the soil, and in its release towards ectomycorrhizal tree roots. We study the involvement of these candidates in phosphate transport from the soil to the mycorrhizal roots using transcriptomic, microscopy, and isotopic approaches.
Our publications on phosphate transport in ectomycorrhizal symbiosis:
Plassard C., Becquer A., Garcia K. (2019) Phosphorus transport in mycorrhiza: how far are we? Trends in Plant Science. 24(9): 794-801.
Becquer A., Garcia K., Plassard C. (2018) HcPT1.2 participates in Pi acquisition in Hebeloma cylindrosporum external hyphae of ectomycorrhizas under high and low phosphate conditions. Plant Signaling & Behavior. 13(10): e1525997.
Becquer A.*, Garcia K.*, Amenc L., Rivard C., Doré J., Trives-Segura C., Szponarski W., Russet S., Baeza Y., Lassalle B., Gay G., Zimmermann S.D., Plassard C. (2018) The Hebeloma cylindrosporum HcPT2 Pi transporter plays a key role in the ectomycorrhizal symbiosis. New Phytologist. 220(4): 1185-1199. (pdf). *co-first authors.
Garcia K., Haider M.Z., Delteil A., Corratgé-Faillie C., Conéjero G., Tatry M.V., Becquer A., Amenc L., Sentenac H., Plassard C., Zimmermann S. (2013) Promoter-dependent expression of the fungal transporter HcPT1.1 under Pi shortage and its spatial localization in ectomycorrhiza. Fungal Genetics and Biology. 58-59C: 53-61.