Mixotrophy in Land Plants: Why To Stay Green?

Mixotrophic orchids do not use photosynthates for perennial underground organs

“…Most plants are autotrophic and interact with soil fungi, forming mycorrhizal symbioses (van der Heijden et al ., ) where plants gain mineral nutrients and provide photosynthates to fungi. Yet, plants repeatedly evolve heterotrophy (Tĕšitel et al ., ), and several lineages, especially in orchids, import carbon from their mycorrhizal fungi, a strategy called mycoheterotrophy (Merckx, ). Green plants that are photosynthetic but also import carbon from their mycorrhizal fungi have raised considerable interest over the past two decades (Julou et al ., ; Selosse & Roy, ).…”

In situ transcriptomic and metabolomic study of the loss of photosynthesis in the leaves of mixotrophic plants exploiting fungi

“…The absence of a major metabolic response to albinism specific to these orchids has to be considered in the framework of the mixotrophic status of these species, which inherently rely on fungal nutrients for rhizome resources (Gonneau et al, 2014;Lallemand et al, 2019) and during early shoot development at least Gonneau et al, 2014;Tĕ sitel et al, 2018). Indeed, green individuals in mixotrophic species already handle the restriction of photosynthesis during their vegetative growth, due to environmental conditions (Julou et al, 2005) or limited intrinsic photosynthetic abilities (Girlanda et al, 2006).…”

“…Indeed, green individuals in mixotrophic species already handle the restriction of photosynthesis during their vegetative growth, due to environmental conditions (Julou et al, 2005) or limited intrinsic photosynthetic abilities (Girlanda et al, 2006). However, fruits and seeds are more dependent on photosynthetates, especially from capsules and leaves (Bellino et al, 2014;Gonneau et al, 2014;Suetsugu et al, 2018;Tĕ sitel et al, 2018;Lallemand et al, 2019), and make limited use of fungal nutrients, either for physiological reasons or because fungal mycorrhizal colonization reaches a minimum at fruiting time Gonneau et al, 2014).…”

“…Unlike the usual mycorrhizal symbiosis, mycoheterotrophic plants get both their mineral nutrients and organic carbon from their mycorrhizal fungi (Merckx, 2013). With more than 500 fully mycoheterotrophic species that have lost chlorophyll and photosynthesis, this remarkable evolutionary inversion of mutualistic mycorrhizal interactions has arisen independently at least 50 times, in 17 plant families (Merckx et al, 2013a;Tĕ sitel et al, 2018). However, we have yet to understand the metabolic evolution to mycoheterotrophy .…”

“…In addition to full mycoheterotrophs, some green plants obtain their carbon by adding photosynthesis and partial mycoheterotrophy in a strategy called mixotrophy (Selosse and Roy, 2009;Tĕ sitel et al, 2018). Orchids have complex links with mycoheterotrophy and mixotrophy (Bidartondo et al, 2004;Selosse et al, 2004;Roy et al, 2013).…”