Identification and Functional Characterization of CsMYCs in Cucumber Glandular Trichome Development

CmMYC2-CmMYBML1 module orchestrates the resistance to herbivory by synchronously regulating the trichome development and constitutive terpene biosynthesis in Chrysanthemum

Trichomes are specialized epidermal outgrowths covering the aerial parts of most terrestrial plants. There is a large species variability in occurrence of different types of trichomes such that the molecular regulatory mechanism underlying the formation and the biological function of trichomes in most plant species remain unexplored. Here, we used Chrysanthemum morifolium as a model plant to explore the regulatory network in trichome formation and terpenoid synthesis and unravel the physical and chemical roles of trichomes in constitutive defense against herbivore feeding. By analyzing the trichome-related genes from transcriptome database of the trichomes-removed leaves and intact leaves, we identified CmMYC2 to positively regulate both development of T-shaped and glandular trichomes as well as the content of terpenoids stored in glandular trichomes. Furthermore, we found that the role of CmMYC2 in trichome formation and terpene synthesis was mediated by interaction with CmMYBML1. Our results reveal a sophisticated molecular mechanism wherein the CmMYC2-CmMYBML1 feedback inhibition loop regulates the formation of trichomes (non-glandular and glandular) and terpene biosynthesis, collectively contributing to the enhanced resistance to Spodoptera litura larvae feeding. Our findings provide new insights into the novel regulatory network by which the plant synchronously regulates trichome density for the physical and chemical defense against herbivory.

Advances in Molecular Plant Sciences

In recent years, as biotechnological advancements have continued to unfold, our understanding of plant molecular biology has undergone a remarkable transformation [...].

Zinc Finger-Homeodomain Transcriptional Factors (ZHDs) in Cucumber (Cucumis sativus L.): Identification, Evolution, Expression Profiles, and Function under Abiotic Stresses

Cucumber (Cucumis sativus L.) is a globally prevalent and extensively cultivated vegetable whose yield is significantly influenced by various abiotic stresses, including drought, heat, and salinity. Transcription factors, such as zinc finger-homeodomain proteins (ZHDs), a plant-specific subgroup of Homeobox, play a crucial regulatory role in stress resistance. In this study, we identified 13 CsZHDs distributed across all six cucumber chromosomes except chromosome 7. Phylogenetic analysis classified these genes into five clades (ZHDI-IV and MIF) with different gene structures but similar conserved motifs. Collinearity analysis revealed that members of clades ZHD III, IV, and MIF experienced amplification through segmental duplication events. Additionally, a closer evolutionary relationship was observed between the ZHDs in Cucumis sativus (C. sativus) and Arabidopsis thaliana (A. thaliana) compared to Oryza sativa (O. sativa). Quantitative real-time PCR (qRT-PCR) analysis demonstrated the general expression of CsZHD genes across all tissues, with notable expression in leaf and flower buds. Moreover, most of the CsZHDs, particularly CsZHD9-11, exhibited varying responses to drought, heat, and salt stresses. Virus-induced gene silencing (VIGS) experiments highlighted the potential functions of CsZHD9 and CsZHD10, suggesting their positive regulation of stomatal movement and responsiveness to drought stress. In summary, these findings provide a valuable resource for future analysis of potential mechanisms underlying CsZHD genes in response to stresses.

The dual role of GoPGF reveals that the pigment glands are synthetic sites of gossypol in aerial parts of cotton

Gossypol and the related terpenoids are stored in the pigment gland to protect cotton plants from biotic stresses, but little is known about the synthetic sites of these metabolites. Here, we showed that GoPGF, a key gene regulating gland formation, was expressed in gland cells and roots. The chromatin immunoprecipitation sequencing (ChIP-seq) analysis demonstrated that GoPGF targets GhJUB1 to regulate gland morphogenesis. RNA-sequencing (RNA-seq) showed high accumulation of gossypol biosynthetic genes in gland cells. Moreover, integrated analysis of the ChIP-seq and RNA-seq data revealed that GoPGF binds to the promoter of several gossypol biosynthetic genes. The cotton callus overexpressing GoPGF had dramatically increased the gossypol levels, indicating that GoPGF can directly activate the biosynthesis of gossypol. In addition, the gopgf mutant analysis revealed the existence of both GoPGF-dependent and -independent regulation of gossypol production in cotton roots. Our study revealed that the pigment glands are synthetic sites of gossypol in aerial parts of cotton and that GoPGF plays a dual role in regulating gland morphogenesis and gossypol biosynthesis. The study provides new insights for exploring the complex relationship between glands and the metabolites they store in cotton and other plant species.

QTL mapping and stability analysis of trichome density in zucchini (Cucurbita pepo L.)

Trichomes provide an excellent model for studying cell differentiation and proliferation. The aboveground tissues of plants with long dense trichomes (LDTs) can cause skin itching in people working in a zucchini field, in which management, pollination, and fruit harvesting are difficult. In this study, an F2 population was constructed with the LDT inbred line "16" and the sparse micro trichome (SMT) inbred line "63" for QTL analysis of type I and II trichome density. Two QTLs were identified on chromosomes 3 and 15 using the QTL-seq method. Additionally, 191 InDel markers were developed on 20 chromosomes, a genetic map was constructed for QTL mapping, and three QTLs were identified on chromosomes 3, 6, and 15. Two QTLs, CpTD3.1 and CpTD15.1, were identified in both QTL-seq and genetic map-based QTL analyses, and CpTD15.1 was the major-effect QTL. The stability of CpTD3.1 and CpTD15.1 was confirmed using data from F2 plants under different environmental conditions. The major-effect QTL CpTD15.1 was located between markers chr15-4991349 and chr15-5766791, with a physical distance of 775.44 kb, and explained 12.71%-29.37% of the phenotypic variation observed in the three environments. CpTD3.1 was located between markers chr3-218350 and chr3-2891236, in a region with a physical distance of 2,672.89 kb, and explained 5.00%-10.64% of the phenotypic variation observed in the three environments. The functional annotations of the genes within the CpTD15.1 region were predicted, and five genes encoding transcription factors regulating trichome development were selected. Cp4.1LG15g04400 encoded zinc finger protein (ZFP) and harbored nonsynonymous SNPs in the conserved ring finger domain between the two parental lines. There were significant differences in Cp4.1LG15g04400 expression between "16" and "63", and a similar pattern was found between germplasm resources of LDT lines and SMT lines. It was presumed that Cp4.1LG15g04400 might regulate trichome density in zucchini. These results lay a foundation for better understanding the density of multicellular nonglandular trichomes and the regulatory mechanism of trichome density in zucchini.