title: Chemical and transcriptional responses of Norway spruce genotypes with different susceptibility to Heterobasidion spp. infection.
abstract: BACKGROUND
  Norway spruce [Picea abies (L.) Karst.] is one of the most important conifer species in Europe. The wood is economically important and infections by wood-rotting fungi cause substantial losses to the industry.The first line of defence in a Norway spruce tree is the bark. It is a very efficient barrier against infection based on its mechanical and chemical properties. Once an injury or an infection is recognized by the tree, induced defences are activated. In this study we examined transcriptional response, using 454-sequencing, and chemical profiles in bark of Norway spruce trees with different susceptibility to Heterobasidion annosum s.l. infection. The aim was to find associations between the transcriptome and chemical profiles to the level of susceptibility to Heterobasidion spp. in Norway spruce genotypes.
  
  
  RESULTS
  Both terpene and phenol compositions were analysed and at 28 days post inoculation (dpi) high levels of 3-carene was produced in response to H. annosum. However, significant patterns relating to inoculation or to genotypes with higher or lower susceptibility could only be found in the phenol fraction. The levels of the flavonoid catechin, which is polymerized into proanthocyanidins (PA), showed a temporal variation; it accumulated between 5 and 15 dpi in response to H. annosum infection in the less susceptible genotypes. The transcriptome data suggested that the accumulation of free catechin was preceded by an induction of genes in the flavonoid and PA biosynthesis pathway such as leucoanthocyanidin reductase. Quantitative PCR analyses verified the induction of genes in the phenylpropanoid and flavonoid pathway. The qPCR data also highlighted genotype-dependent differences in the transcriptional regulation of these pathways.
  
  
  CONCLUSIONS
  The varying dynamics in transcriptional and chemical patterns displayed by the less susceptible genotypes suggest that there is a genotypic variation in successful spruce defence strategies against Heterobasidion. However, both high levels of piceasides and flavonoids in the less susceptible genotypes suggested the importance of the phenolic compounds in the defence. Clearly an extended comparison of the transcriptional responses in the interaction with Heterobasidion between several independent genotypes exhibiting reduced susceptibility is needed to catalogue mechanisms of successful host defence strategies.
authors: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Sweden.
authors: Marie
authors: M
authors: Danielsson
authors: Karl
authors: K
authors: Lundén
authors: Malin
authors: M
authors: Elfstrand
authors: Jiang
authors: J
authors: Hu
authors: Tao
authors: T
authors: Zhao
authors: Jenny
authors: J
authors: Arnerup
authors: Katarina
authors: K
authors: Ihrmark
authors: Gunilla
authors: G
authors: Swedjemark
authors: Anna-Karin
authors: AK
authors: Borg-Karlson
authors: Jan
authors: J
authors: Stenlid
mesh_terms: D001487:Basidiomycota / Q000472:pathogenicity*; D000081008:Bicyclic Monoterpenes; D002392:Catechin / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D016000:Cluster Analysis; D008401:Gas Chromatography-Mass Spectrometry; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D039821:Monoterpenes / Q000032:analysis; D010636:Phenols / Q000032:analysis; D028222:Picea / Q000737:chemistry* / Q000235:genetics* / Q000382:microbiology; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology; D013548:Sweden; D013729:Terpenes / Q000032:analysis; D059467:Transcriptome
chemical_list: D000081008:Bicyclic Monoterpenes; D039821:Monoterpenes; D010636:Phenols; D013729:Terpenes; D002392:Catechin; C030218:3-carene