Transport in Plants I

Zimmermann, Martina; Milburn, J. A.

doi:10.1007/978-3-642-66161-7

Cited by 66 publications

(1 citation statement)

References 255 publications

(359 reference statements)

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“…Although, thiamine, pantothenate, coenzyme A, niacin, pyridoxal and biotin can be found in the phloem (free or bounded to transporter proteins) (Pirson and Zimmermann, 1975), their concentrations might be not sufficient for many phloem-feeding species. This could explain why the capability to produce some of these compounds has been kept in bacterial endosymbionts while it has been lost in others.…”

Section: Discussionmentioning

confidence: 99%

To B or not to B: Arsenophonus as a source of B-vitamins in whiteflies

Santos-García

Juravel

Freilich

et al. 2018

Preprint

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and francisco.silva@uv.es AbstractInsect lineages feeding on nutritionally restricted diets such as phloem, xylem, or blood, were able to diversify by acquiring bacterial species that complemented the missing nutrients. These bacteria, considered obligate/primary endosymbionts, share a long evolutionary history with their hosts. In some cases, however, these endosymbionts are not able to fulfill all the nutritional requirements of their host, driving the acquisition of additional symbiotic species. Whiteflies, which feed on phloem, established an obligate relationship with Candidatus Portiera aleyrodidarum, who provides essential amino acids and carotenoids to the host. As many Whiteflies species harbor additional endosymbionts, they could provide their hosts with missing nutrients. To test this hypothesis, genomes of several endosymbionts from the whiteflies Aleurodicus dispersus, A. floccissimus and Trialeurodes vaporariorum were sequenced and analyzed. All three species were found to harbor an endosymbiont from the genus Arsenophonus, and the two former also host Wolbachia. A comparative analysis of the three Arsenophonus genomes revealed that although all of them are capable of synthesizing B-vitamins and cofactors, such as pyridoxal, riboflavin, or folate, their genomes and phylogenetic relationship vary greatly. Arsenophonus of A. floccissimus and T. vaporariorum belong to the same clade and display characteristics of facultative endosymbionts, such as large genomes (3 Mb) with thousands of genes, many pseudogenes, intermediate GC content, and mobile genetic elements (MGEs). In contrast, Arsenophonus of A. dispersus belongs to a different lineage and displays the characteristics of a primary endosymbiont, such as a reduced genome (670 kb) with 400 genes, 32% GC content, and no MGEs. However, the presence of 274 pseudogenes suggests that this symbiotic association is more recent than other reported hemipteran's primary endosymbionts. Arsenophonus of A. dispersus gene repertoire is completely integrated in the symbiotic consortia, and the biosynthesis of most vitamins occurs in shared pathways with its host. In addition, Wolbachia have also retained the ability to produce riboflavin, FAD, and folate, and may have a nutritional contribution. Taken together, our results show that Arsenophonus have a pivotal place in whiteflies nutrition by their ability to produce B-vitamins, even if they diverge and/or go through a genome reduction process.

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Section: Discussionmentioning

confidence: 99%

To B or not to B: Arsenophonus as a source of B-vitamins in whiteflies

Santos-García

Juravel

Freilich

et al. 2018

Preprint

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The Floral and Extra‐floral Nectaries of Passiflora. I. The Floral Nectary

Durkee

1981

American J of Botany

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Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane‐bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre‐nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.

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