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Steroidal glycoalkaloids (SGAs) are specialized metabolites in Solanaceae that serve as defensive compounds and undergo significant compositional changes during fruit ripening. This study explored the roles of transcription factors SlNOR and SlNOR-like1 in SGAs biosynthesis during tomato fruit development. UPLC-MS/MS revealed dynamic changes in four major SGAs: tomatidine, β-tomatine, α-tomatine, and Esculeoside A. Transgenic studies with knockout and overexpression lines demonstrated that both SlNOR and SlNOR-like1 positively regulated SGAs accumulation. RT-qPCR analysis showed that these transcription factors modulated multiple GAME genes in the SGAs biosynthetic pathway. Through EMSA and DLR assays, we established that SlNOR and SlNOR-like1 directly bound to and activated GAME25 and GAME40 promoters, two key genes involved in tomatidine synthesis and α-tomatine conversion, respectively. These findings reveal a previously unknown regulatory mechanism of SGAs metabolism and suggest potential strategies for optimizing tomato fruit quality through molecular breeding., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)

(22S,25S)-5alpha-tomatanin-3beta-ol, N-acetyl-(22S,25S)-5alpha-tomatanin-3beta-ol, (22R,25R)-5alpha-tomatanin-3beta-ol and (22R, 25S)-22, 26-epimino-5alpha-cholestane-3beta, 16beta, 16beta-diol are transformed by Nocardia restrictus into corresponding 3alpha-ol compounds with yields from 7o to 5%.

The planar distribution of 3-beta-hydroxysterols in the plasmalemma of the green flagellate Chlamydomonas reinhardii has been studied with the freeze-fracture technique using the polyene antibiotic filipin and the saponin tomatin as cytochemical markers. Filipin-sterol complexes were predominantly observed as 25 to 30 nm protuberances on the E-face of the plasmalemma with corresponding invaginations on the P-face. Generally filipin-sterol and tomatin-sterol complexes were randomly distributed, but were virtually absent from sites of intramembrane particle arrays (IMP-arrays, i.e. the flagellar necklace, the flagellar bracelet including strut arrays, the eyespot membrane). The results suggest that IMP-arrays of Chlamydomonas are deficient in 3-beta-hydroxysterols and may therefore be regarded as special lipid arrays. IMP-arrays might require an altered lipid environment for proper function. Some functional aspects of IMP-arrays in Chlamydomonas are discussed.