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Copyright of Acta Agriculturae Zhejiangensis is the property of Acta Agriculturae Zhejiangensis Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The symplasmic phloem-unloading pathway is interrupted by an apoplasmic pathway in developing Xanthoceras sorbifolia fruit. • Sucrose influx XsSWEET10 as a key candidate is involved in sugar transport. • SUSY acts as the key enzyme catalyzing the progress of Suc degradation post-unloading pathways in pericarp and the seeds. • VINV (vacuolar acid invertase) and NINV (neutral invertase) play a compensation role in sucrose decomposition. • Sucrose phosphate synthase (SPS) played more important role in sucrose synthesis in pericarp and seeds. The process of phloem unloading and post-unloading transport of photoassimilate is critical to crop output. Xanthoceras sorbifolia is a woody oil species with great biomass energy prospects in China; however, underproduction of seeds seriously restricts its development. Here, our cytological studies by ultrastructural observation revealed that the sieve element-companion cell complex in carpellary bundle was symplasmically interconnected with surrounding parenchyma cells at the early and late fruit developmental stages, whereas it was symplasmically isolated at middle stage. Consistently, real-time imaging showed that fluorescent tracer 6(5)carboxyfluorescein was confined to phloem strands at middle stage but released into surrounding parenchymal cells at early and late stages. Enzymatic assay showed that sucrose synthase act as the key enzyme catalyzing the progress of Suc degradation post-unloading pathway whether in pericarp or in seed, while vacuolar acid invertase and neutral invertase play compensation roles in sucrose decomposition. Sugar transporter XsSWEET10 had a high expression profile in fruit, especially at middle stage. XsSWEET10 is a plasma membrane-localized protein and heterologous expression in SUC2- deficient yeast strain SUSY7/ura3 confirmed its ability to uptake sucrose. These findings approved the transition from symplasmic to apoplasmic phloem unloading in Xanthoceras sorbifolia fruit and XsSWEET10 as a key candidate in sugar transport. [ABSTRACT FROM AUTHOR]

The grain-filling process is crucial for cereal crop yields, but how the caryopsis of such plants is supplied with sugars, which are produced by photosynthesis in leaves and then transported long distance, is largely unknown. In rice (Oryza sativa), various SWEET family sucrose transporters are thought to have important roles in grain filling. Here, we report that OsSWEET14 plays a crucial part in this process in rice. ossweet14 knockout mutants did not show any detectable phenotypic differences from the wild type, whereas ossweet14;ossweet11 double-knockout mutants had much more severe phenotypes than ossweet11 single-knockout mutants, including strongly reduced grain weight and yield, reduced grain-filling rate, and increased starch accumulation in the pericarp. Both OsSWEET14 and OsSWEET11 exhibited distinct spatiotemporal expression patterns between the early stage of caryopsis development and the rapid grain-filling stage. During the rapid grain-filling stage, OsSWEET14 and OsSWEET11 localized to four key sites: vascular parenchyma cells, the nucellar projection, the nucellar epidermis, and cross cells. These results demonstrate that OsSWEET14 plays an important role in grain filling, and they suggest that four major apoplasmic pathways supply sucrose to the endosperm during the rapid grain-filling stage via the sucrose effluxers SWEET14 and SWEET11., (Copyright © 2021 Elsevier B.V. All rights reserved.)