Abstract
The olive leaf trichomes are multicellular peltate hairs densely distributed mainly at the lower leaf epidermis. Although, non-glandular, they have gained much attention since they significantly contribute to abiotic and biotic stress tolerance of olive leaves. The exact mechanisms by which olive trichomes achieve these goals are not fully understood. They could act as mechanical barrier but they also accumulate high amounts of flavonoids among other secondary metabolites. However, little is currently known about the exact compounds they produce and the respective metabolic pathways. Here we present the first EST analysis from olive leaf trichomes by using 454-pyrosequencing. A total of 5368 unigenes were identified out of 7258 high quality reads with an average length of 262 bp. Blast search revealed that 27.5% of them had high homologies to known proteins. By using Blast2GO, 1079 unigenes (20.1%) were assigned at least one Gene Ontology (GO) term. Most of the genes were involved in cellular and metabolic processes and in binding functions followed by catalytic activity. A total of 521 transcripts were mapped to 67 KEGG pathways. Olive trichomes represent a tissue of highly unique transcriptome as per the genes involved in developmental processes and the secondary metabolism. The results indicate that mature olive trichomes are trancriptionally active, mainly through the potential production of enzymes that contribute to phenolic compounds with important roles in biotic and abiotic stress responses.
Highlights
Trichomes are epidermal appendages on leaves or other vegetative and reproductive aerial organs
EST Analysis and Annotation of Transcripts Since the olive genome has not been sequenced as yet and the olive trichome represents a highly specialized tissue, we applied 454-pyrosequencing which results in long read lengths
Considering that we identified several transcripts encoding ribosomal proteins along with factors involved in initiation of transcription or translation (Table S2), it is plausible that the protein synthesis machinery in olive trichomes is very active
Summary
Trichomes are epidermal appendages on leaves or other vegetative and reproductive aerial organs. They are widespread in the plant kingdom, while their morphology varies substantially among tissue and species. They are categorized into two major groups: glandular trichomes and non-glandular trichomes, referred to as “simple hairs”. Accumulate, and often secrete a variety of secondary metabolites, such as terpenes, fatty acid derivatives, alkaloids or defense proteins, most of which protect the plant from abiotic and biotic stresses (Eisner et al, 1998; Iijima et al, 2004; Schilmiller et al, 2008). Significant efforts have been made to elucidate their biosynthetic pathways and to manipulate
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