The Lotus japonicus Genome

14

Plant-Specialized Metabolism and Its

Genomic Organization in Biosynthetic

Gene Clusters in Lotus japonicus

Adam M. Takos and Fred Rook

Abstract

Plants produce a wide spectrum of specialized metabolites that function in

plant chemical defense against pathogens and herbivores or have signaling

roles in the interaction with other organisms. The plant-specialized

metabolites that have received most attention in legumes in general, and in

Lotus japonicus as a legume model species, are proanthocyanidins,

isoflavonoids, cyanogenic and non-cyanogenic hydroxynitrile glucosides,

and triterpenoids. Here, we review these four classes of plant-specialized

metabolites in terms of the specific compounds produced byL. japonicus,

the biosynthetic genes responsible, and the genomic organization of the

genes. We previously reported that inL. japonicus,the non-homologous

genes encoding the complete biosynthetic pathway for the cyanogenic

glucosides lotaustralin and linamarin are organized in a gene cluster. Here,

we additionally describe gene clusters in theL. japonicusgenome for

triterpenoidandisoflavonoidbiosynthesis.Amodelexplaininghowselection

for reduced recombination results in gene cluster formation is presented.

14.1 Plant-Specialized Metabolism
in Legumes

Plants species produce a large number and wide
diversity of specialized metabolites, also known as
secondary metabolites, which function in the
interaction between the plant and its environment.
Many of these compounds have a role as chemical

defense compounds, protecting the plant against

herbivores or combatting bacterial and fungal

infections. Other compounds serve roles in

attracting pollinators, or specifically forflavonoids

in legumes, have a signaling role in the interaction

with symbiotic bacteria. Four classes of such

plant-specialized metabolites have received most

attention in legumes: proanthocyanidins, isofl-

avonoids, triterpenoids, and cyanogenic gluco-

sides (Fig.14.1). This attention is partly due to the

importance of forage legumes to animal nutrition

and the effects these compounds have on digestion

and animal health. In addition, plant chemical

defense and its evolution are a topic of major sci-

entific interest. The genomic organization of these

biosynthetic pathways inLotus japonicusreveals

A.M. Takos
F. Rook (&)
Plant Biochemistry Laboratory, Department of Plant
and Environmental Sciences, University of
Copenhagen, Thorvaldsensvej 40, 1871
Frederiksberg, Denmark
e-mail: [email protected]

S. Tabata and J. Stougaard (eds.),The Lotus japonicus Genome, Compendium of Plant Genomes,
DOI 10.1007/978-3-662-44270-8_14,©Springer-Verlag Berlin Heidelberg 2014

149