Laccase gene expression as a possible key adaptation for herbivorous niche expansion in the attine fungus-growing ants

TY - CONF

T1 - Laccase gene expression as a possible key adaptation for herbivorous niche expansion in the attine fungus-growing ants

AU - de Fine Licht, Henrik Hjarvard

AU - Schiøtt, Morten

AU - Nygaard, Sanne

AU - Boomsma, Jacobus Jan

N1 - Conference code: 16

PY - 2010

Y1 - 2010

N2 - Fungus garden enzyme activity is crucial for sustaining societies of attine ants. The evolutionary diversification of this clade has likely been influenced by enzymatic specialization in connection to changes in foraging niche (De Fine Licht, Schiøtt, Mueller & Boomsma, 2010, Evolution), particularly when the ancestral leaf-cutting ants shifted from a diet of mostly fresh but shed plant material to actively cutting leaves. However, the way in which leaf-cutting ants managed to overcome the chemical defences of leaves has remained poorly understood. Here we document that laccases may have played an important role in allowing the leaf-cutting ants to become generalist functional herbivores. Laccases are polyphenol oxidase enzymes (PPOs) that are best known for their ability to degrade lignin in saprophytic and wood-pathogenic fungi. We found that laccase activity was primarily expressed in newly constructed garden sections where secondary leaf compounds are most likely to hinder decomposition. A combination of genomic and transcriptional analyses showed that there are at least eight copies of putative laccase coding genes in a draft genome of the fungal symbiont Leucocoprinus gongylophorus and that these are differentially expressed. We hypothesize that fungus garden laccases originally had a lignin-degrading function in the fungi that the attine ants domesticated, consistent with the gardens of lower attine ants processing only dry plant substrate. Our results would then suggest that some of these laccases were co-opted for the derived function of neutralizing phenolic secondary defences in leaves. Selection for increased gene expression of fungal laccase genes in the ancestral leaf-cutting ant symbiont could thus have gradually increased the ant’s capacity to process a higher proportion of fresh leaves in their forage. We are currently investigating the molecular evolution and expression profiles of these multiple laccase genes.

AB - Fungus garden enzyme activity is crucial for sustaining societies of attine ants. The evolutionary diversification of this clade has likely been influenced by enzymatic specialization in connection to changes in foraging niche (De Fine Licht, Schiøtt, Mueller & Boomsma, 2010, Evolution), particularly when the ancestral leaf-cutting ants shifted from a diet of mostly fresh but shed plant material to actively cutting leaves. However, the way in which leaf-cutting ants managed to overcome the chemical defences of leaves has remained poorly understood. Here we document that laccases may have played an important role in allowing the leaf-cutting ants to become generalist functional herbivores. Laccases are polyphenol oxidase enzymes (PPOs) that are best known for their ability to degrade lignin in saprophytic and wood-pathogenic fungi. We found that laccase activity was primarily expressed in newly constructed garden sections where secondary leaf compounds are most likely to hinder decomposition. A combination of genomic and transcriptional analyses showed that there are at least eight copies of putative laccase coding genes in a draft genome of the fungal symbiont Leucocoprinus gongylophorus and that these are differentially expressed. We hypothesize that fungus garden laccases originally had a lignin-degrading function in the fungi that the attine ants domesticated, consistent with the gardens of lower attine ants processing only dry plant substrate. Our results would then suggest that some of these laccases were co-opted for the derived function of neutralizing phenolic secondary defences in leaves. Selection for increased gene expression of fungal laccase genes in the ancestral leaf-cutting ant symbiont could thus have gradually increased the ant’s capacity to process a higher proportion of fresh leaves in their forage. We are currently investigating the molecular evolution and expression profiles of these multiple laccase genes.

M3 - Poster

T2 - 16th Congress of international union for the study of social insects

Y2 - 8 August 2010 through 14 August 2010

ER -