Increase in Phloem Area in the Tomato hawaiian skirt Mutant Is Associated with Enhanced Sugar Transport

Abstract

The Hawaiian skirt (HWS) gene has been described in Arabidopsis, rice, tomato and poplar where it seems to perform distinct functions with relatively little overlap. In tomato, alteration of the gene function confers facultative parthenocarpy, thought to be a consequence of changes in the microRNA metabolism. In the rice mutant, improvement in panicle architecture is associated with an increase in grain yield. Knowing that hws tomato fruits show a higher Brix level, it was suspected that vascular bundles might also be altered in this species, in a similar fashion to the rice phenotype. The pedicel structure of the hws-1 line was therefore examined under the microscope and sugar concentrations from phloem exudate were determined in an enzymatic assay. A distinct increase in the phloem area was observed as well as a higher sugar content in mutant phloem exudates, which is hypothesized to contribute to the high Brix level in the mutant fruits. Furthermore, the described phenotype in this study bridges the gap between Arabidopsis and rice phenotypes, suggesting that the modulation of the microRNA metabolism by HWS influences traits of agricultural interest across several species.

Sugar loading of crop seeds – a partnership of phloem, plasmodesmal and membrane transport

“…Such investigations might be strengthened through including phloem development mutants (e.g. Lombardo et al ., 2021; Nam et al ., 2022). Do plasmodesmata located at se‐ccc/vascular parenchyma interfaces regulate sucrose import into developing seeds?…”

“…Such investigations might be strengthened through including phloem development mutants (e.g. Lombardo et al, 2021;Nam et al, 2022).…”

Variations in Pedicel Structural Properties Among Four Pear Species (Pyrus): Insights Into the Relationship Between the Fruit Characteristics and the Pedicel Structure

“…In tomato, Li et al (2021) found that the water deficit did not change the hydraulic resistance and the vascular structure in the pedicel; however, this could not provide any clue about how the structural differences of vascular affect the hydraulic transport in the plant. A mutant tomato ( hws-1 ) with wider phloem and narrower xylem rings showed a higher sugar concentration in the phloem exudates and a higher Brix level in the fruit, indicating that the increased phloem area ratio contributes to the higher fruit Brix in tomatoes ( Lombardo et al, 2021 ). In grape, Shigyoku ( Vitis vinifera ) showed 1.8-fold greater phloem area of the pedicel than that of Heukboseok ( V. vinifera ) after veraison, based on the number of cells constituting the phloem, whereas no difference of xylem area was found between them; the cell number and area of the phloem contributed to the accumulation of sugars and the main constituents of the cell wall, thus maintaining the firmness of grapes until late maturity; therefore, the phloem structure was considered to contribute to the increased softening of Heukboseok grapes ( Jung et al, 2016 ).…”

Revisiting yield in terms of phloem transport to grains suggests phloem sap movement might be homeostatic

“…Two recent reviews have suggested that improving phloem loading or unloading could be an avenue to improve crop yield (Braun et al, 2014; Reynolds et al, 2021). In several species including rice, phloem transport capacity has been suggested to play a role in grain, seed or fruit production (Deng et al, 2021; Lombardo et al, 2021; Nam et al, 2022; You et al, 2021; Zhai et al, 2023). To our knowledge, there is no overview of phloem transport properties amongst wheat cultivars and thus potential relationships with yield are not well known.…”