Evolution, function and manipulation of methyl halide production in plants

Methyl halides (CH3Cl, CH3Br and CH3I) are a group of volatile organic compounds which contribute to natural ozone degradation in the atmosphere. Plants are important emitters of these compounds due to the activity of halide/thiol methyltransferases (HTMTs), however, the function of HTMTs or methyl halide production is not known. In Arabidopsis thaliana, one HTMT is primarily responsible for the production of methyl halides and encoded by the HARMLESS TO OZONE LAYER (HOL) gene. In this study, an A. thaliana hol mutant and 35S::HOL lines were used to investigate the function of HOL. No support was found for the hypothesis that HOL contributes to salt stress tolerance via the disposal of excessive amounts of halides. On the contrary, increased HOL activity made 35S::HOL plants more susceptible towards salt stress. Despite the toxicity of methyl halides, differences in HOL activity in hol mutant and 35S::HOL plants did not affect the performance of insect herbivores, nor did it alter the microbial diversity of the rhizosphere in these lines. Microarray analysis of WT and hol mutant plants pointed to a function of HOL in starch/carbon metabolism and stress response pathways in A. thaliana. Brassica crops are significant emitters of methyl halides. A HOL-homologous gene (BraA.HOL.a) was identified in Brassica rapa. It was confirmed that this gene contributes to methyl halide production in B. rapa since braA.hol.a mutants had significantly reduced emission levels compared to WT. HOL-homologous genes were also found in various plant species throughout the plant kingdom including the moss Physcomitrella patens, which was shown to produce CH3Br. These data show that methyl halide production is an ancient mechanism in land plants. Moreover, phylogenetic analysis revealed a clear separation between HTMTs from glucosinolate (GL)-containing plants and HTMTs from eudicots without GLs supporting the hypothesis of a novel function of HTMTs in the order Brassicales.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2012

Author dc:creator

• Koerner, Evelyn

Language dc:language

en