Ying Li

SUMMARY: Trichomes are basic and important barriers necessary for plants to resist environmental stress. Although several regulatory transcription factors have been found to play an important role in tomato ( Solanum lycopersicum ) multicellular trichome development, the regulatory network underlying trichome density in tomato is still limited. Our results demonstrated that a non‐specific lipid transfer protein gene, SlnsLTP33 , was identified as a downstream target gene of the trichome regulator SlHDZIV8 (an HD‐Zip IV transcription factor). By knocking out or co‐suppressing the SlnsLTP33 gene, tomato plants exhibit fewer trichomes, while overexpressing plants exhibit more trichomes. We found that SlnsLTP33 directly interacts with SlHDZIV8 or CUTIN DEFICIENT2 (CD2) and synergistically activates the transcriptional activity of SlCycB2 by binding to the promoter of SlCycB2 . Collectively, our data uncover the essential role of the SlHDZIV8/CD2‐SlnsLTP33 regulatory module in regulating multicellular trichome density in tomato. Further research has shown that SlnsLTP33 plays a crucial role in the accumulation of glycerophospholipids, glycerides, and fatty acyl, which may be closely related to trichome development. Our findings provide a novel gene and new insights into the regulatory network controlling trichome formation in tomato.

Summary: Tomato (Solanum lycopersicum) stands as one of the most valuable vegetable crops globally, and fruit firmness significantly impacts storage and transportation. To identify genes governing tomato firmness, we scrutinized the firmness of 266 accessions from core collections. Our study pinpointed an ethylene receptor gene, SlEIN4, located on chromosome 4 through a genome‐wide association study (GWAS) of fruit firmness in the 266 tomato core accessions. A single‐nucleotide polymorphism (SNP) (A → G) of SlEIN4 distinguished lower (AA) and higher (GG) fruit firmness genotypes. Through experiments, we observed that overexpression of SlEIN4^AA significantly delayed tomato fruit ripening and dramatically reduced fruit firmness at the red ripe stage compared with the control. Conversely, gene editing of SlEIN4^AA with CRISPR/Cas9 notably accelerated fruit ripening and significantly increased fruit firmness at the red ripe stage compared with the control. Further investigations revealed that fruit firmness is associated with alterations in the microstructure of the fruit pericarp. Additionally, SlEIN4^AA positively regulates pectinase activity. The transient transformation assay verified that the SNP (A → G) on SlEIN4 caused different genetic effects, as overexpression of SlEIN4^GG increased fruit firmness. Moreover, SlEIN4 exerts a negative regulatory role in tomato ripening by impacting ethylene evolution through the abundant expression of ethylene pathway regulatory genes. This study presents the first evidence of the role of ethylene receptor genes in regulating fruit firmness. These significant findings will facilitate the effective utilization of firmness and ripening traits in tomato improvement, offering promising opportunities for enhancing tomato storage and transportation capabilities.

Trade-offs between survival and growth are widely observed in plants. Melon is an annual, trailing herb that produces economically valuable fruits that are traditionally cultivated in early spring in China. Melon seedlings are sensitive to low temperatures, and thus usually suffer from cold stress during the early growth period. However, little is known about the mechanism behind the trade-offs between seedling cold tolerance and fruit quality in melon. In this study, a total of 31 primary metabolites were detected from the mature fruits of eight melon lines that differ with respect to seedling cold tolerance; these included 12 amino acids, 10 organic acids, and nine soluble sugars. Our results showed that concentrations of most of the primary metabolites in the cold-resistant melons were generally lower than in the cold-sensitive melons; the greatest difference in metabolite levels was observed between the cold-resistant line H581 and the moderately cold-resistant line HH09. The metabolite and transcriptome data for these two lines were then subjected to WGCNA, resulting in the identification of five key candidate genes underlying the balancing between seedling cold tolerance and fruit quality. Among these genes, CmEAF7 might play multiple roles in regulating chloroplast development, photosynthesis, and the ABA pathway. Furthermore, multi-method functional analysis showed that CmEAF7 can certainly improve both seedling cold tolerance and fruit quality in melon. Our study identified an agriculturally important gene, CmEAF7, and provides a new insight into breeding methods to develop melon cultivars with seedling cold tolerance and high fruit quality.

Plant height is an important target trait for crop genetic improvement. Our previous work has identified a salt-tolerant C2H2 zinc finger, SlZF3, and its overexpression lines also showed a semi-dwarf phenotype, but the molecular mechanism remains to be elucidated. Here, we characterized the dwarf phenotype in detail. The dwarfism is caused by a decrease in stem internode cell elongation and deficiency of bioactive gibberellic acids (GAs), and can be rescued by exogenous GA3 treatment. Gene expression assays detected reduced expression of genes in the GA biosynthesis pathway of the overexpression lines, including SlGA20ox4. Several protein–DNA interaction methods confirmed that SlZF3 can directly bind to the SlGA20ox4 promoter and inhibit its expression, and the interaction can also occur for SlKS and SlKO. Overexpression of SlGA20ox4 in the SlZF3-overexpressing line can recover the dwarf phenotype. Therefore, SlZF3 regulates plant height by directly repressing genes in the tomato GA biosynthesis pathway.

SUMMARY: Folate (vitamin B9) is important for plant root development, but the mechanism is largely unknown. Here we characterized a root defective mutant, folb2, in Arabidopsis, which has severe developmental defects in the primary root. The root apical meristem of the folb2 mutant is impaired, and adventitious roots are frequently found at the root–hypocotyl junction. Positional cloning revealed that a 61‐bp deletion is present in the predicted junction region of the promoter and the 5′ untranslated region of AtFolB2, a gene encoding a dihydroneopterin aldolase that functions in folate biosynthesis. This mutation leads to a significant reduction in the transcript level of AtFolB2. Liquid chromatography–mass spectrometry analysis showed that the contents of the selected folate compounds were decreased in folb2. Arabidopsis AtFolB2 knockdown lines phenocopy the folb2 mutant. On the other hand, the application of exogenous 5‐formyltetrahydrofolic acid could rescue the root phenotype of folb2, indicating that the root phenotype is indeed related to the folate level. Further analysis revealed that folate could promote rootward auxin transport through auxin transporters and that folate may affect particular auxin/indole‐3‐acetic acid proteins and auxin response factors. Our findings provide new insights into the important role of folic acid in shaping root structure.

The RanBP2-type zinc finger (RBZ) protein genes, which are well-characterized in animals, are involved in the regulation of mRNA processing. Although they are diversely distributed in plants, their functions still remain largely unknown. In this study, we performed a comprehensive bioinformatic analysis of 22 RBZ genes in tomato. The gene structure analysis revealed that the SlRBZ genes have 2 to 17 exons. SlRBZ proteins contain typical conserved domains, including Motif 1 or Motif 2, or a combination of Motif 9 and Motif 4. Two paralogous pairs were identified in the tomato. Segmental duplication possibly contributed to the expansion of the SlRBZ genes in tomato. Interestingly, the SlRBZ15 gene generated four products, yielded by alternative splicing. A cis-regulatory element analysis revealed that SlRBZ genes might be involved in the complex regulatory networks during plant growth and development. The expression profiles of the SlRBZ genes were analyzed in different tissues using eight phytohormones and four abiotic stress treatments based on RNA sequencing data and qRT-PCR verification. The results showed that each gene responded differently to more than one phytohormone or abiotic stress type. This research provides a foundation for future functional research on SlRBZ genes in tomato.

The response regulators (RRs) that function as components in two-component systems play important roles in cytokinin signal transduction, plant development, and abiotic stress resistance. However, identification and functional characterization of RR gene family were not available in melon to date. In this study, a total of 18 CmRRs were identified across 11 out of 12 melon chromosomes and classified into three groups, type A, type B and clock PRR in the phylogenetic tree. A variety of abiotic stresses and hormone-related cis-elements were found in the promoters of CmRR genes, implying that these genes could respond to diverse abiotic stresses in plants. Most of CmRR genes exhibited tissue-specific expression patterns and some of CmRRs were cold-induced based on two sets of RNA-seq data. qRT-PCR assays confirmed that CmRR2/11/15 and CmPRR2/3 were up-regulated and CmRR6 was down-regulated under cold treatment. Further, the tobacco ringspot virus (TRSV) system was carried out to verify the gene function of CmRR6 and CmPRR3 which represent cold-induced CmRR genes. Silencing CmRR6 or CmPRR3 could significantly improve cold tolerance of melon plants, which were supported by determination of Chl fluorescence, ion leakage, reactive oxygen, proline and malondialdehyde in the virus-induced gene silencing (VIGS) plants. Finally, CmRR2/6 and CmPRR3 were predicted to interact with several classical cold-associated proteins; split luciferase complementation assay verified an interact between CmRR6 and CmARF5. Our findings suggest that CmRRs might contribute to biological functions under cold stress and provide new insights for further pursuing CmRRs molecular mechanisms underlying cold tolerance in melon.