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Summary Plant genetic transformation is a crucial step for applying biotechnology such as genome editing to basic and applied plant science research. Its success primarily relies on the efficiency of gene delivery into plant cells and the ability to regenerate transgenic plants. In this study, we have examined the effect of several developmental regulators (DRs), including PLETHORA (PLT5), WOUND INDUCED DEDIFFERENTIATION 1 (WIND1), ENHANCED SHOOT REGENERATION (ESR1), WUSHEL (WUS) and a fusion of WUS and BABY‐BOOM (WUS‐P2A‐BBM), on in planta transformation through injection of Agrobacterium tumefaciens in snapdragons (Antirrhinum majus). The results showed that PLT5, WIND1 and WUS promoted in planta transformation of snapdragons. An additional test of these three DRs on tomato (Solanum lycopersicum) further demonstrated that the highest in planta transformation efficiency was observed from PLT5. PLT5 promoted calli formation and regeneration of transformed shoots at the wound positions of aerial stems, and the transgene was stably inherited to the next generation in snapdragons. Additionally, PLT5 significantly improved the shoot regeneration and transformation in two Brassica cabbage varieties (Brassica rapa) and promoted the formation of transgenic calli and somatic embryos in sweet pepper (Capsicum annum) through in vitro tissue culture. Despite some morphological alternations, viable seeds were produced from the transgenic Bok choy and snapdragons. Our results have demonstrated that manipulation of PLT5 could be an effective approach for improving in planta and in vitro transformation efficiency, and such a transformation system could be used to facilitate the application of genome editing or other plant biotechnology application in modern agriculture.

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The functions of sucrose transporters (SUTs) differ among family members. The physiological function of SUT1 has been studied intensively, while that of SUT4 in various plant species including tomato (Solanum lycopersicum) is less well understood. In this study, we characterized the function of tomato SlSUT4 in the regulation of flowering using a combination of molecular and physiological analyses. SlSUT4 displayed transport activity for sucrose when expressed in yeast (Saccharomyces cerevisiae), and it localized at both the plasma membrane and tonoplast. SlSUT4 interacted with SlSUT1, causing partial internalization of the latter, the main phloem loader of sucrose in tomato. Silencing of SlSUT4 promoted SlSUT1 localization to the plasma membrane, contributing to increased sucrose export and thus increased sucrose level in the shoot apex, which promoted flowering. Both silencing of SlSUT4 and spraying with sucrose suppressed gibberellin biosynthesis through repression of ent-kaurene oxidase and gibberellin 20-oxidase-1 (two genes encoding key enzymes in gibberellin biosynthesis) expression by SlMYB76, which directly bound to their promoters. Silencing of SlMYB76 promoted gibberellin biosynthesis. Our results suggest that SlSUT4 is a functional sucrose transporter in tomato; down-regulation of SlSUT4 expression enhances sucrose transport to the shoot apex, which promotes flowering by inhibiting gibberellin biosynthesis.

Snapdragon (Antirrhinum majus) has long been a very popular perennial in the United States due to its unique flower shape with a range of striking colors (Huo and Chen, 2018). Based on their height, snapdragons are typically classified into three categories: dwarf (6-15 inches), medium (1-2 feet), and tall (6-15 feet) . The dwarf variety has a dense, bushy growth pattern, producing numerous flower spikes. They grow on average 6 to 15 inches tall and are ideal plants for use as low borders or in containers. Mid-sized varieties grow 1-2 feet tall and are typically used in borders (either alone or with other bedding plants) and sometimes as cut flowers. Tall varieties range anywhere from 2 to 3 feet in height (Gilman et al. 2018). The magnificent flowers with a wide range of petal colors atop the long green spikes make the tall variety a desirable cut flower for container, bouquets, or gardens. In 2015, fresh-cut snapdragon sales increased 51.7% from 2010 and reached $12.93 million, making it a top ten fresh cut flower in United States（USDA, 2015). With all of their aesthetic attributes and versatility, snapdragons are also an important model system for genetics and molecular studies of various plant processes.   For example, snapdragon pigmentation mutants produced by transposon (a type of mobile DNAs) mutagenesis have provided researchers a good way to study anthocyanin biosynthesis and subsequently aid plant breeders in developing new varieties with novel flower colors (Jackson et al. 1992). Furthermore, snapdragon has a mechanism by which transposable mutations can be regulated into active and inactive states through temperature control (Hashida et al., 2006). Advantages of this elegant transposon mutagenesis system and how it relates to plant breeding are described in this paper.