Mutualism Within a Simulated Microgravity Environment - Piriformospora indica Promotes the Growth of Medicago truncatula

Abstract The endophytic fungus, Piriformospora indica, developed a subepidermal infection within Medicago truncatula at 1 g and at simulated microgravity over a period of 15 days, resulting in intracellular colonization of mature host tissue. At 1 g, P. indica inoculation affected the growth and morphology of M. truncatula, predominantly roots. Inoculated M. truncatula had a significantly greater number of roots (102%), total root length (88%), and dry root weight (25%) than non-inoculated plants. Effects on shoot morphology of P. indica inoculated M. truncatula included longer (31%) and heavier (30%) shoots, along with increased leaf surface area (98%). P. indica retained the ability to promote the growth of M. truncatula under simulated microgravity conditions upon two dimensional clinostatic rotation, significantly increasing root number by 51% and root length by 48%. These physiological and morphological changes may mitigate biotic and abiotic stresses that would otherwise limit crop productivity.