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Summary: Abiotic stresses affect plant growth and development by causing cellular damage and/or restricting resources. Plants often respond to stresses through abscisic acid (ABA) signaling. Exogenous ABA application can therefore be used to mimic stress responses, which can be overridden by glucose (Glc) addition during seed germination. It remains unclear whether ABA‐mediated germination inhibition is due to regional or global suppression of Glc availability in germinating Arabidopsis seeds.We used a genetically engineered Förster resonance energy transfer (FRET) sensor to ascertain whether ABA affects the spatiotemporal distribution of Glc, 14C‐Glc uptake assays to track potential effects of ABA on sugar import, and transcriptome and mutant analyses to identify genes associated with Glc availability that are involved in ABA‐inhibited seed germination.Abscisic acid limits Glc in the hypocotyl largely by suppressing sugar allocation as well as altering sugar metabolism. Mutant plants carrying loss‐of‐function ABA‐inducible sucrose‐phosphate synthase (SPS) genes accumulated more Glc, leading to ABA‐insensitive germination. We reveal that Glc antagonizes ABA by globally counteracting the ABA influence at the transcript level, including expansin (EXP) family genes suppressed by ABA.This study presents a new perspective on how ABA affects Glc distribution, which likely reflects what occurs when seeds are subjected to abiotic stresses such as drought and salt stress. [ABSTRACT FROM AUTHOR]

Soybean accounts for more than half of the global production of oilseed and more than a quarter of the protein used globally for human food and animal feed. Soybean domestication involved parallel increases in seed size and oil content, and a concomitant decrease in protein content. However, science has not yet discovered whether these effects were due to selective pressure on a single gene or multiple genes. Here, re-sequencing data from >800 genotypes revealed a strong selection during soybean domestication on GmSWEET10a. The selection of GmSWEET10a conferred simultaneous increases in soybean-seed size and oil content as well as a reduction in the protein content. The result was validated using both near-isogenic lines carrying substitution of haplotype chromosomal segments and transgenic soybeans. Moreover, GmSWEET10b was found to be functionally redundant with its homologue GmSWEET10a and to be undergoing selection in current breeding, leading the the elite allele GmSWEET10b , a potential target for present-day soybean breeding. Both GmSWEET10a and GmSWEET10b were shown to transport sucrose and hexose, contributing to sugar allocation from seed coat to embryo, which consequently determines oil and protein contents and seed size in soybean. We conclude that past selection of optimal GmSWEET10a alleles drove the initial domestication of multiple soybean-seed traits and that targeted selection of the elite allele GmSWEET10b may further improve the yield and seed quality of modern soybean cultivars. [ABSTRACT FROM AUTHOR]

Dedicated water channels are involved in the facilitated diffusion of water molecules across the cell membrane in plants. Transporter proteins are also known to transport water molecules along with substrates, however the molecular mechanism of water permeation is not well understood in plant transporters. Here, we show plant sugar transporters from the SWEET ( S ugar W ill E ventually be E xported T ransporter) family act as water-conducting carrier proteins via a variety of passive and active mechanisms that allow diffusion of water molecules from one side of the membrane to the other. This study provides a molecular perspective on how plant membrane transporters act as water carrier proteins, a topic that has not been extensively explored in literature. Water permeation in membrane transporters could occur via four distinct mechanisms which form our hypothesis for water transport in SWEETs. These hypothesis are tested using molecular dynamics simulations of the outward-facing, occluded, and inward-facing state of AtSWEET1 to identify the water permeation pathways and the flux associated with them. The hydrophobic gates at the center of the transport tunnel act as a barrier that restricts water permeation. We have performed in silico single and double mutations of the hydrophobic gate residues to examine the changes in the water conductivity. Surprisingly, the double mutant allows the water permeation to the intracellular half of the membrane and forms a continuous water channel. These computational results are validated by experimentally examining the transport of hydrogen peroxide molecules by the AtSWEET family of transporters. We have also shown that the transport of hydrogen peroxide follows the similar mechanism as water transport in AtSWEET1. Finally, we conclude that similar water-conduction states are also present in other SWEET transporters due to the high sequence and structure conservation exhibited by this transporter family.

Sweet sorghum has emerged as a promising source of bioenergy mainly due to its high biomass and high soluble sugar yield in stems. Studies have shown that loss-of-function Dry locus alleles have been selected during sweet sorghum domestication, and decapitation can further boost sugar accumulation in sweet sorghum, indicating that the potential for improving sugar yields is yet to be fully realized. To maximize sugar accumulation, it is essential to gain a better understanding of the mechanism underlying the massive accumulation of soluble sugars in sweet sorghum stems in addition to the Dry locus. We performed a transcriptomic analysis upon decapitation of near-isogenic lines for mutant ( d , juicy stems, and green leaf midrib) and functional ( D , dry stems and white leaf midrib) alleles at the Dry locus. Our analysis revealed that decapitation suppressed photosynthesis in leaves, but accelerated starch metabolic processes in stems. SbbHLH093 negatively correlates with sugar levels supported by genotypes ( DD vs. dd ), treatments (control vs. decapitation), and developmental stages post anthesis (3d vs.10d). D locus gene SbNAC074A and other programmed cell death-related genes were downregulated by decapitation, while sugar transporter-encoding gene SbSWEET1A was induced. Both SbSWEET1A and Invertase 5 were detected in phloem companion cells by RNA in situ assay. Loss of the SbbHLH093 homolog , AtbHLH093 , in Arabidopsis led to a sugar accumulation increase. This study provides new insights into sugar accumulation enhancement in bioenergy crops, which can be potentially achieved by reducing reproductive sink strength and enhancing phloem unloading., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Xue, Beuchat, Wang, Yu, Moose, Chen and Chen.)

Galactose is an abundant and essential sugar used for the biosynthesis of many macromolecules in different organisms, including plants. Galactose metabolism is tightly and finely controlled, since excess galactose and its derivatives are inhibitory to plant growth. In Arabidopsis (Arabidopsis thaliana), root growth and pollen germination are strongly inhibited by excess galactose. However, the mechanism of galactose-induced inhibition during pollen germination remains obscure. In this study, we characterized a plasma membrane-localized transporter, Arabidopsis Sugars Will Eventually be Exported Transporter 5, that transports glucose and galactose. SWEET5 protein levels started to accumulate at the tricellular stage of pollen development and peaked in mature pollen, before rapidly declining after pollen germinated. SWEET5 levels are responsible for the dosage-dependent sensitivity to galactose, and galactokinase is essential for these inhibitory effects during pollen germination. However, sugar measurement results indicate that galactose flux dynamics and sugar metabolism, rather than the steady-state galactose level, may explain phenotypic differences between sweet5 and Col-0 in galactose inhibition of pollen germination., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

It has long been recognized that stomatal movement modulates CO 2 availability and as a consequence the photosynthetic rate of plants, and that this process is feedback-regulated by photoassimilates. However, the genetic components and mechanisms underlying this regulatory loop remain poorly understood, especially in monocot crop species. Here, we report the cloning and functional characterization of a maize ( Zea mays ) mutant named closed stomata1 ( cst1 ). Map-based cloning of cst1 followed by confirmation with the clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR associated protein 9 system identified the causal mutation in a Clade I Sugars Will Eventually be Exported Transporters (SWEET) family gene, which leads to the E81K mutation in the CST1 protein. CST1 encodes a functional glucose transporter expressed in subsidiary cells, and the E81K mutation strongly impairs the oligomerization and glucose transporter activity of CST1. Mutation of CST1 results in reduced stomatal opening, carbon starvation, and early senescence in leaves, suggesting that CST1 functions as a positive regulator of stomatal opening. Moreover, CST1 expression is induced by carbon starvation and suppressed by photoassimilate accumulation. Our study thus defines CST1 as a missing link in the feedback-regulation of stomatal movement and photosynthesis by photoassimilates in maize., (© 2019 American Society of Plant Biologists. All rights reserved.)