Germacrene A Synthases for Sesquiterpene Lactone Biosynthesis Are Expressed in Vascular Parenchyma Cells Neighboring Laticifers in Lettuce
Sesquiterpene lactone (STL) and natural rubber (NR) are characteristic isoprenoids in lettuce ( ). Both STL and NR co-accumulate in laticifers, pipe-like structures located along the vasculature. NR-biosynthetic genes are exclusively expressed in laticifers, but cell-type specific expression of STL-...
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Published in | Plants (Basel) Vol. 11; no. 9; p. 1192 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Switzerland
MDPI AG
28.04.2022
MDPI |
Subjects | |
Online Access | Get full text |
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Summary: | Sesquiterpene lactone (STL) and natural rubber (NR) are characteristic isoprenoids in lettuce (
). Both STL and NR co-accumulate in laticifers, pipe-like structures located along the vasculature. NR-biosynthetic genes are exclusively expressed in laticifers, but cell-type specific expression of STL-biosynthetic genes has not been studied. Here, we examined the expression pattern of germacrene A synthase (
), which catalyzes the first step in STL biosynthesis in lettuce. Quantitative PCR and Illumina read mapping revealed that the transcripts of two
isoforms (
/
) are expressed two orders of magnitude (~100-200) higher in stems than laticifers. This result implies that the cellular site for
/
expression is not in laticifers. To gain more insights, promoters of
/
were cloned and fused to β-glucuronidase (
), followed by transformations of lettuce with these promoter-
constructs. In in situ GUS assays, the
expression driven by the
promoters was tightly associated with vascular bundles. High-resolution microsections showed that GUS signals are not present in laticifers but are detected in the vascular parenchyma cells neighboring the laticifers. These results suggest that expression of
occurs in the parenchyma cells neighboring laticifers, while the resulting STL metabolites accumulate in laticifers. It can be inferred that active metabolite-trafficking occurs from the parenchyma cells to laticifers in lettuce. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 These authors contributed equally to this work. Present address: Department of Plant Biochemistry, University of Göttingen, Justus-von-Liebig-Weg 11 Göttingen, D-37077 Göttingen, Germany. Present address: Department of Chemistry, Irving K. Barber Faculty of Science, University of British Columbia, Kelowna, BC V1V 1V7, Canada. |
ISSN: | 2223-7747 2223-7747 |
DOI: | 10.3390/plants11091192 |