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Summary: The complexity of compound leaves results primarily from the leaflet initiation and arrangement during leaf development. However, the molecular mechanism underlying compound leaf development remains a central research question.SlTCP24 and SlTCP29, two plant‐specific transcription factors with the conserved TCP motif, are shown here to synergistically regulate compound leaf development in tomato. When both of them were knocked out simultaneously, the number of leaflets significantly increased, and the shape of the leaves became more complex. SlTCP24 and SlTCP29 could form both homodimers and heterodimers, and such dimerization was impeded by the leaf polarity regulator SlAS2, which interacted with SlTCP24 and SlTCP29.SlTCP24 and SlTCP29 could bind to the TCP‐binding cis‐element of the SlCKX2 promoter and activate its transcription. Transgenic plants with SlTCP24 and SlTCP29 double‐gene knockout had a lowered transcript level of SlCKX2 and an elevated level of cytokinin.This work led to the identification of two key regulators of tomato compound leaf development and their targeted genes involved in cytokinin metabolic pathway. A model of regulation of compound leaf development was proposed based on observations of this study. [ABSTRACT FROM AUTHOR]

Trichomes are specialized glandular or non-glandular structures that provide physical or chemical protection against insect and pathogen attack. Trichomes in Arabidopsis have been extensively studied as typical non-glandular structures. By contrast, the molecular mechanism underlying glandular trichome formation and elongation remains largely unknown. We previously demonstrated that Hair is essential for the formation of type I and type VI trichomes. Here, we found that overexpression of Hair increased the density and length of tomato trichomes. Biochemical assays revealed that Hair physically interacts with its close homolog SlZFP8-like (SlZFP8L), and SlZFP8L also directly interacts with Woolly. SlZFP8L -overexpressing plants showed increased trichome density and length. We further found that the expression of SlZFP6 , which encodes a C2H2 zinc finger protein, is positively regulated by Hair. Using chromatin immunoprecipitation, yeast one-hybrid, and dual-luciferase assays we identified that SlZFP6 is a direct target of Hair. Similar to Hair and SlZFP8L , the overexpression of SlZFP6 also increased the density and length of tomato trichomes. Taken together, our results suggest that Hair interacts with SlZFP8-like to regulate the initiation and elongation of trichomes by modulating SlZFP6 expression in tomato. [ABSTRACT FROM AUTHOR]

Summary: Plant hormones can adjust the physiology and development of plants to enhance their adaptation to biotic and abiotic challenges. Jasmonic acid (JA), one of the immunity hormones in plants, triggers genome‐wide transcriptional changes in response to insect attack and wounding. Although JA is known to affect the development of trichomes, epidermal appendages that form a protective barrier against various stresses, it remains unclear how JA interacts with developmental programs that regulate trichome development.In this study, we show that JA affects trichome length in tomato by releasing the transcriptional repression mediated by Jasmonate ZIM (JAZ) proteins. We identified SlJAZ4, a negative regulator preferentially expressed in trichomes, as the critical component in JA signaling in tomato trichomes.We also identified a homeodomain‐leucine zipper gene, SlHD8, as the downstream regulator of JA signaling that promotes trichome elongation. SlHD8 is also highly expressed in trichomes and physically interacts with SlJAZ4. Loss‐of‐function mutations in SlHD8 caused shorter trichomes, a phenotype that was only partially rescued by methyl jasmonate treatment.Our dual‐luciferase and chromatin immunoprecipitation–quantitative PCR assays revealed that SlHD8 regulates trichome elongation by directly binding to the promoters of a set of cell‐wall‐loosening protein genes and activating their transcription. Together, our findings define SlHD8‐SlJAZ4 as a key module mediating JA‐induced trichome elongation in tomato. [ABSTRACT FROM AUTHOR]

Trichomes are specialized epidermal appendages that serve as excellent models to study cell morphogenesis. Although the molecular mechanism underlying trichome morphogenesis in Arabidopsis has been well characterized, most of the regulators essential for multicellular trichome morphology remain unknown in tomato. In this study, we determined that the recessive hairless-2 (hl-2) mutation in tomato causes severe distortion of all trichome types, along with increased stem fragility. Using map-based cloning, we found that the hl-2 phenotype was associated with a 100 bp insertion in the coding region of Nck-associated protein 1, a component of the SCAR/WAVE complex. Direct protein-protein interaction was detected between Hl-2 and Hl (SRA1, specifically Rac1-associated protein) using yeast two-hybrid and co-immunoprecipitation assays, suggesting that these proteins may work together during trichome formation. In addition, knock-down of a HD-Zip IV transcription factor, HDZIPIV8 , distorted trichomes similar to the hl-2 mutant. HDZIPIV8 regulates the expression of Hl-2 by binding to the L1-box in the Hl-2 promoter region, and is involved in organizing actin filaments. The brittleness of hl-2 stems was found to result from decreased cellulose content. Taken together, these findings suggest that the Hl-2 gene plays an important role in controlling multicellular trichome morphogenesis and mechanical properties of stems in tomato plants. [ABSTRACT FROM AUTHOR]

SUMMARY: Cuticular waxes play a crucial role not only in plant defense against biotic and abiotic stresses, but also in the quality and storability of fruits, such as the tomato (Solanum lycopersicum). Although the biosynthetic pathways of waxes have been extensively characterized, the regulatory mechanisms underlying wax biosynthesis in tomato remain largely unclear. Here, we show that Woolly (Wo), a multicellular trichome regulator, is involved in modulating wax biosynthesis in tomato. Wo enhances the expression of the wax biosynthetic genes SlCER6, SlKCR1, and SlPAS2, and the wax transporter gene SlLTP, and thereby promotes wax accumulation. Furthermore, Wo directly binds to the L1‐box in the promoter of SlCER6, an essential element of the very‐long‐chain fatty acid elongase complex. Intriguingly, overexpression (OE) or knock‐down of SlMYB31, an MYB transcription factor that physically interacts with Wo in vivo and in vitro, produces marked changes in wax composition, and whereas Wo knock‐down inhibits wax accumulation in SlMYB31‐OE lines, SlMYB31 knock‐down inhibits wax accumulation in Wo‐OE lines, implying that these two genes function in the same pathway. Lastly, SlCER6 expression is induced by abscisic acid in a manner that is partially dependent on Wo. These results demonstrate that Wo and SlMYB31 cooperatively control tomato cuticular wax biosynthesis by regulating the expression of SlCER6. Significance Statement: Our results uncover a novel molecular mechanism whereby a Wo–SlMYB31 complex regulates cuticular wax biosynthesis in tomato. [ABSTRACT FROM AUTHOR]

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Summary: Carotenoids play important roles in many biological processes, such as light harvesting, photoprotection and visual attraction in plants. However, the regulation of carotenoid biosynthesis is still not fully understood.Here, we demonstrate that SlBBX20, a B‐box (BBX) zinc‐finger transcription factor, is a positive regulator of carotenoid accumulation in tomato (Solanum lycopersicum). Overexpression of SlBBX20 leads to dark green fruits and leaves and higher levels of carotenoids relative to the wild‐type. Interactions between SlBBX20 and DE‐ETIOLATED 1 (SlDET1) lead to the ubiquitination and 26S proteasome‐mediated degradation of SlBBX20. Moreover, deficiencies in the components of the CUL4‐DDB1‐DET1 complex enhanced the stability of the SlBBX20 protein. Thus, we conclude that SlBBX20 is a substrate of the CUL4‐DDB1‐DET1 E3 ligase.SlBBX20 can activate the expression of PHYTOENE SYNTHASE 1, encoding a key enzyme in carotenoid biosynthesis, by directly binding to a G‐box motif in its promoter, which results in the elevated levels of carotenoids in SlBBX20 overexpression lines.We identified a key regulator of carotenoid biosynthesis and demonstrated that the stability of SlBBX20 is regulated by ubiquitination. These findings provide us a new target for the genetic improvement of the nutritional quality of tomato fruit. [ABSTRACT FROM AUTHOR]

As a primary source of lycopene in the human diet, fleshy fruits synthesize this compound both de novo and via chlorophyll metabolism during ripening. Sl SGR1 encodes a STAY-GREEN protein that plays a critical role in the regulation of chlorophyll degradation in tomato leaves and fruits., We report that Sl SGR1 can regulate tomato ( Solanum lycopersicum) lycopene accumulation through direct interaction with a key carotenoid synthetic enzyme Sl PSY1, and can inhibit its activity. This interaction with Sl SGR1 mediates lycopene accumulation during tomato fruit maturation. We confirmed this inhibitory activity in bacteria engineered to produce lycopene, where the introduction of Sl SGR1 reduced dramatically lycopene biosynthesis., The repression of Sl SGR1 in transgenic tomato fruits resulted in altered accumulation patterns of phytoene and lycopene, whilst simultaneously elevating Sl PSY1 m RNA accumulation and plastid conversion at the early stages of fruit ripening, resulting in increased lycopene and β-carotene (four- and nine-fold, respectively) in red ripe fruits., Sl SGR1 influences ethylene signal transduction via the altered expression of ethylene receptor genes and ethylene-induced genes. Fruit shelf-life is extended significantly in Sl SGR1-repressed tomatoes. Our results indicate that Sl SGR1 plays a pivotal regulatory role in color formation and fruit ripening regulation in tomato, and further suggest that Sl SGR1 activity is mediated through direct interaction with PSY1. [ABSTRACT FROM AUTHOR]