Nectar biosynthesis is conserved among floral and extrafloral nectaries

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2021-04
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Chatt, Elizabeth C.
Mahalim, Siti-Nabilla
Mohd-Fadzil, Nur-Aziatull
Roy, Rahul
Klinkenberg, Peter M.
Hampton, Marshall
Carter, Clay J.
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Oxford University Press on behalf of American Society of Plant Biologists
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Nectar is a primary reward mediating plant–animal mutualisms to improve plant fitness and reproductive success. Four distinct trichomatic nectaries develop in cotton (Gossypium hirsutum), one floral and three extrafloral, and the nectars they secrete serve different purposes. Floral nectar attracts bees for promoting pollination, while extrafloral nectar attracts predatory insects as a means of indirect protection from herbivores. Cotton therefore provides an ideal system for contrasting mechanisms of nectar production and nectar composition between different nectary types. Here, we report the transcriptome and ultrastructure of the four cotton nectary types throughout development and compare these with the metabolomes of secreted nectars. Integration of these datasets supports specialization among nectary types to fulfill their ecological niche, while conserving parallel coordination of the merocrine-based and eccrine-based models of nectar biosynthesis. Nectary ultrastructures indicate an abundance of rough endoplasmic reticulum positioned parallel to the cell walls and a profusion of vesicles fusing to the plasma membranes, supporting the merocrine model of nectar biosynthesis. The eccrine-based model of nectar biosynthesis is supported by global transcriptomics data, which indicate a progression from starch biosynthesis to starch degradation and sucrose biosynthesis and secretion. Moreover, our nectary global transcriptomics data provide evidence for novel metabolic processes supporting de novo biosynthesis of amino acids secreted in trace quantities in nectars. Collectively, these data demonstrate the conservation of nectar-producing models among trichomatic and extrafloral nectaries.
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Systems analyses of key metabolic modules of floral and extrafloral nectaries of cotton
( 2019-11-27) Chatt, Elizabeth ; Mahalim, Siti-Nabilla ; Horner, Harry ; Mohd-Fadzil, Nur-Aziatull ; Roy, Rahul ; Klinkenberg, Peter ; Nikolau, Basil ; Hampton, Marshall ; Carter, Clay ; Department of Genetics, Development, and Cell Biology (LAS)

Nectar is a primary reward mediating plant-animal mutualisms to improve plant fitness and reproductive success. In Gossypium hirsutum (cotton), four distinct trichomatic nectaries develop, one floral and three extrafloral. The secreted floral and extrafloral nectars serve different purposes, with the floral nectar attracting bees to promote pollination and the extrafloral nectar attracting predatory insects as a means of indirect resistance from herbivores. Cotton therefore provides an ideal system to contrast mechanisms of nectar production and nectar composition between floral and extrafloral nectaries. Here, we report the transcriptome, ultrastructure, and metabolite spatial distribution using mass spectrometric imaging of the four cotton nectary types throughout development. Additionally, the secreted nectar metabolomes were defined and were jointly composed of 197 analytes, 60 of which were identified. Integration of theses datasets support the coordination of merocrine-based and eccrine-based models of nectar synthesis. The nectary ultrastructure supports the merocrine-based model due to the abundance of rough endoplasmic reticulum positioned parallel to the cell walls and profusion of vesicles fusing to the plasma membranes. The eccrine-based model which consist of a progression from starch synthesis to starch degradation and to sucrose biosynthesis was supported by gene expression data. This demonstrates conservation of the eccrine-based model for the first time in both trichomatic and extrafloral nectaries. Lastly, nectary gene expression data provided evidence to support de novo synthesis of amino acids detected in the secreted nectars.

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This article is published as Chatt, Elizabeth C., Siti-Nabilla Mahalim, Nur-Aziatull Mohd-Fadzil, Rahul Roy, Peter M. Klinkenberg, Harry T. Horner, Marshall Hampton, Clay J. Carter, and Basil J. Nikolau. "Nectar biosynthesis is conserved among floral and extrafloral nectaries." Plant Physiology 185, no. 4 (2021): 1595-1616. DOI: 10.1093/plphys/kiab018. Copyright 2021 The Author(s). Attribution 4.0 International (CC BY 4.0). Posted with permission.
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