A combination of chitooligosaccharide and lipochitooligosaccharide recognition promotes arbuscular mycorrhizal associations in Medicago truncatula

Plants associate with beneficial arbuscular mycorrhizal fungi facilitating nutrient acquisition. Arbuscular mycorrhizal fungi produce chitooligosaccharides (COs) and lipo-chitooligosaccharides (LCOs), that promote symbiosis signalling with resultant oscillations in nuclear-associated calcium. The activation of symbiosis signalling must be balanced with activation of immunity signalling, which in fungal interactions is promoted by COs resulting from the chitinaceous fungal cell wall. Here we demonstrate that COs ranging from CO4-CO8 can induce symbiosis signalling in Medicago truncatula. CO perception is a function of the receptor-like kinases MtCERK1 and LYR4, that activate both immunity and symbiosis signalling. A combination of LCOs and COs act synergistically to enhance symbiosis signalling and suppress immunity signalling and receptors involved in both CO and LCO perception are necessary for mycorrhizal establishment. We conclude that LCOs, when present in a mix with COs, drive a symbiotic outcome and this mix of signals is essential for arbuscular mycorrhizal establishment.

The effect of burnt soils on growth of Xanthorrhoea glauca subsp. angustifolia (Xanthorrhoeaceae) seedlings in box-ironbark ecosystems, northern central Victoria

Seedlings of Xanthorrhoea glauca subsp. angustifolia D.J.Bedford (Xanthorrhoeaceae) were grown in burnt, unburnt and ash-rich soils from the box-ironbark ecosystem, northern central Victoria. Analysis of root architecture and the chemistry of leaves and roots demonstrate that burning improves seedling biomass development and acquisition of nutrients. An increased uptake of zinc by seedlings after fire is thought to be ecologically important and may infer vesicular-arbuscular mycorrhizal associations. The early development of a secondary root system is likely to contribute to seedling survivorship. Given the observed high adult mortality after managed fuel-reduction fires, the importance of understanding and manipulating recruitment dynamics through an adaptive and strategic fire management of the remaining populations is likely to define the long-term survival of the species in Victoria.