Abstract
BackgroundFloral nectar (FN) contains not only energy-rich compounds to attract pollinators, but also defense chemicals and several proteins. However, proteomic analysis of FN has been hampered by the lack of publically available sequence information from nectar-producing plants. Here we used next-generation sequencing and advanced proteomics to profile FN proteins in the opportunistic outcrossing wild tobacco, Nicotiana attenuata.ResultsWe constructed a transcriptome database of N. attenuata and characterized its nectar proteome using LC-MS/MS. The FN proteins of N. attenuata included nectarins, sugar-cleaving enzymes (glucosidase, galactosidase, and xylosidase), RNases, pathogen-related proteins, and lipid transfer proteins. Natural variation in FN proteins of eleven N. attenuata accessions revealed a negative relationship between the accumulation of two abundant proteins, nectarin1b and nectarin5. In addition, microarray analysis of nectary tissues revealed that protein accumulation in FN is not simply correlated with the accumulation of transcripts encoding FN proteins and identified a group of genes that were specifically expressed in the nectary.ConclusionsNatural variation of identified FN proteins in the ecological model plant N. attenuata suggests that nectar chemistry may have a complex function in plant-pollinator-microbe interactions.
Highlights
Floral nectar (FN) contains energy-rich compounds to attract pollinators, and defense chemicals and several proteins
We found natural variation in FN proteins among different N. attenuata accessions collected across the plant’s native habitat and identified FN proteins through stringent and homology-based database searching against public (NCBInr) and an in-house N. attenuata protein subdatabase
Variations of FN proteins in N. attenuata accessions In the nectar redox cycle proposed by Thornburg and colleagues (2004), NEC1 and NEC5 enzymes produce H2O2 in nectar, and both are highly expressed in an ornamental tobacco [7]
Summary
Floral nectar (FN) contains energy-rich compounds to attract pollinators, and defense chemicals and several proteins. Proteomic analysis of FN has been hampered by the lack of publically available sequence information from nectar-producing plants. We used next-generation sequencing and advanced proteomics to profile FN proteins in the opportunistic outcrossing wild tobacco, Nicotiana attenuata. Floral nectar (FN) is produced in many flowers to promote outcrossing mediated by pollinator visitation [1]. Many are likely not directly involved in attracting or repelling pollinators [8,9], but rather function in sugar metabolism as well as in defense against microorganism proliferation, largely through the production of strong oxidants, such as hydrogen peroxide (H2O2) [10]. The over-accumulation of H2O2 produced by FN proteins has been shown to affect
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