Abstract
BackgroundSimple non-isoprenoid hydrocarbons accumulate in discrete regions of the biosphere, including within bacteria and algae as a carbon and/or energy store, and the cuticles of plants and insects, where they may protect against environmental stresses. The extracellular cuticular surfaces of the stigmatic silks of maize are rich in linear hydrocarbons and therefore provide a convenient system to study the biological origins and functions of these unique metabolites.ResultsTo test the hypotheses that genetics and environment influence the accumulation of surface hydrocarbons on silks and to examine the breadth of metabolome compositions across diverse germplasm, cuticular hydrocarbons were analyzed on husk-encased silks and silks that emerged from the husk leaves from 32 genetically diverse maize inbred lines, most of which are commonly utilized in genetics experiments. Total hydrocarbon accumulation varied ~ 10-fold among inbred lines, and up to 5-fold between emerged and husk-encased silks. Alkenes accounted for 5-60% of the total hydrocarbon metabolome, and the majority of alkenes were monoenes with a double bond at either the 7th or 9th carbon atom of the alkyl chain. Total hydrocarbon accumulation was impacted to similar degrees by genotype and husk encasement status, whereas genotype predominantly impacted alkene composition. Only minor differences in the metabolome were observed on silks that were emerged into the external environment for 3- versus 6-days. The environmental influence on the metabolome was further investigated by growing inbred lines in 2 years, one of which was warmer and wetter. Inbred lines grown in the drier year accumulated up to 2-fold more hydrocarbons and up to a 22% higher relative abundance of alkenes. In summary, the surface hydrocarbon metabolome of silks is primarily governed by genotype and husk encasement status, with smaller impacts of environment and genotype-by-environment interactions.ConclusionsThis study reveals that the composition of the cuticular hydrocarbon metabolome on silks is affected significantly by genetic factors, and is therefore amenable to dissection using quantitative genetic approaches. Such studies will clarify the genetic mechanisms responsible for the accumulation of these metabolites, enabling detailed functional investigations of the diverse and complex protective roles of silk surface lipids against environmental stresses.
Highlights
Simple non-isoprenoid hydrocarbons accumulate in discrete regions of the biosphere, including within bacteria and algae as a carbon and/or energy store, and the cuticles of plants and insects, where they may protect against environmental stresses
To test the hypothesis that genetics and environment significantly affect the accumulation of surface hydrocarbons on maize silks, we evaluated the breadth of metabolome compositions for 32 genetically diverse maize inbred lines, including founders of the Nested Association Mapping (NAM) population [27], which provides the future ability to genetically dissect these traits either in a NAM or other genetic mapping framework
In this study, we surveyed cuticular surface hydrocarbon accumulation on silks from 32 genetically diverse maize inbred lines, including nine inbred lines selected from previously identified groupings of maize inbred lines that harbor high genome-wide diversity [28], four “expiredplant variety protection” commercial inbred lines, and 19 of the genetically diverse founder inbred lines of the maize NAM population [27] (Table 1)
Summary
Simple non-isoprenoid hydrocarbons accumulate in discrete regions of the biosphere, including within bacteria and algae as a carbon and/or energy store, and the cuticles of plants and insects, where they may protect against environmental stresses. The cuticle is produced and secreted by epidermal cells and consists of a polyester cutin matrix, which is embedded with and coated by a complex mixture of unique, and readily extractable, non-polar extracellular cuticular surface lipids [1, 2]. These surface lipid metabolites, commonly referred to as cuticular waxes or cuticular lipids, can include very-long chain fatty acids (VLCFAs) of 20 carbons or greater and derivatives of these VLCFAs, including fatty aldehydes, primary and secondary alcohols, wax esters, and hydrocarbons. Silks are rich in hydrocarbons, comprising 40-90% of the silk surface lipid metabolome in specific inbred lines [18,19,20]
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