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As a plant-specific transcription factor, lateral organ boundaries domain (LBD) protein was reported to regulate plant growth and stress response, but the functional research of subfamily II genes is limited. SlMYC2, a master regulator of Jasmonic acid response, has been found to exhibit high expression levels in fruit and has been implicated in the regulation of fruit ripening and resistance to Botrytis. However, its role in fruit expansion remains unknown. In this study, we present evidence that a subfamily II member of LBD, namely SlLBD40, collaborates with SlMYC2 in the regulation of fruit expansion. Overexpression of SlLBD40 significantly promoted fruit growth by promoting mesocarp cell expansion, while knockout of SlLBD40 showed the opposite result. Similarly, SlMYC2 knockout resulted in a significant decrease in cell expansion within the fruit. Genetic analysis indicated that SlLBD40-mediated cell expansion depends on the expression of SlMYC2. SlLBD40 bound to the promoter of SlEXPA5, an expansin gene, but did not activate its expression directly. While, the co-expression of SlMYC2 and SlLBD40 significantly stimulated the activation of SlEXPA5, leading to an increase in fruit size. SlLBD40 interacted with SlMYC2 and enhanced the stability and abundance of SlMYC2. Furthermore, SlMYC2 directly targeted and activated the expression of SlLBD40, which is essential for SlLBD40-mediated fruit expansion. In summary, our research elucidates the role of the interaction between SlLBD40 and SlMYC2 in promoting cell expansion in tomato fruits, thus providing novel insights into the molecular genetics underlying fruit growth., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Jasmonic acid (JA) is a key regulator of plant defense responses. Although the transcription factor MYC2, the master regulator of the JA signaling pathway, orchestrates a hierarchical transcriptional cascade that regulates the JA responses, only a few transcriptional regulators involved in this cascade have been described. Here, we identified the basic helix-loop-helix (bHLH) transcription factor gene in tomato (Solanum lycopersicum), METHYL JASMONATE (MeJA)-INDUCED GENE (SlJIG), the expression of which was strongly induced by MeJA treatment. Genetic and molecular biology experiments revealed that SlJIG is a direct target of MYC2. SlJIG knockout plants generated by gene editing had lower terpene contents than the wild type from the lower expression of TERPENE SYNTHASE (TPS) genes, rendering them more appealing to cotton bollworm (Helicoverpa armigera). Moreover, SlJIG knockouts exhibited weaker JA-mediated induction of TPSs, suggesting that SlJIG may participate in JA-induced terpene biosynthesis. Knocking out SlJIG also resulted in attenuated expression of JA-responsive defense genes, which may contribute to the observed lower resistance to cotton bollworm and to the fungus Botrytis cinerea. We conclude that SlJIG is a direct target of MYC2, forms a MYC2-SlJIG module, and functions in terpene biosynthesis and resistance against cotton bollworm and B. cinerea., (© 2022 Institute of Botany, Chinese Academy of Sciences.)

In tomato, red color is a key commercial trait and arises from the accumulation of carotenoids. Previous studies have revealed that melatonin promotes lycopene accumulation and ethylene production. However, it is unclear if melatonin similarly increases other carotenoids, and whether any increase of carotenoids in tomato fruit is directly related to ethylene production. In this study, changes in carotenoid profiles during fruit ripening were investigated in control (CK) and in fruits treated with melatonin (M50). The α, β-carotene, and lycopene levels were significantly increased in M50, and there was increased carotenoid biosynthetic gene expression. We also observed up-regulated transcript levels of SlRIN, SlCNR, and SlNOR in M50 compared to CK. To better understand the regulation of carotenoid biosynthesis by melatonin and its potential response to endogenous ethylene, we tested an ethylene-insensitive mutant, Never ripe (Nr). Melatonin-treated Nr failed to accumulate more carotenoids compared to CK, although there was significantly changed ethylene production. Additionally, there was no general upregulation of expression of ripening-related genes in this mutant under melatonin treatment. These results suggest melatonin function might require ethylene to promote carotenoid synthesis in tomato., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The SNAT enzyme participates in the biosynthesis of melatonin, which is reported to regulate thermotolerance in many plants. However, the mechanistic basis of this regulation remains unclear. In this study, we identified the SlSNAT gene, which is responsible for melatonin biosynthesis in tomato. SlSNAT expression levels were 3- and 5-fold higher in SlSNAT overexpression lines OX-2 and OX-6, respectively. The melatonin levels were 3- and 4-fold higher than those in wild type. The melatonin levels decreased by 50% when the expression of SlSNAT was downregulated to 40%. Overexpression of SlSNAT in tomato plants provided significantly enhanced thermotolerance with better growth performance in Photosystem II (PSII) maximum photochemical quantum yield (Fv/Fm) and alleviated heat injury. Both exogenous melatonin treatment and endogenous melatonin manipulation by SlSNAT overexpression decreased the levels of reactive oxygen species�accumulation and Fv/Fm. The SlSNAT overexpression line showed protected ribulose bisphosphate carboxylase oxygenase proteins and upregulated response of heat transcription factors and heat shock proteins under heat stress. HSP40, a DnaJ-type chaperone, was found to interact with SlSNAT in the chloroplast. Downregulation of HSP40 showed lower melatonin synthesis under heat stress. HSP40 functions as a chaperone to protect the SNAT enzyme during melatonin synthesis under heat stress. HSP40 interacted with SlSNAT and together participated in melatonin-related thermotolerance regulation in tomato., (� The Author(s) 2020. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)