Advance in sex differentiation in cucumber

Research on the function of CsMYB36 based on an effective hair root transformation system

The hairy root induction system was used to efficiently investigate gene expression and function in plant root. Cucumber is a significant vegetable crop worldwide, with shallow roots, few lateral roots, and weak root systems, resulting in low nutrient absorption and utilization efficiency. Identifying essential genes related to root development and nutrient absorption is an effective way to improve the growth and development of cucumbers. However, genetic mechanisms underlying cucumber root development have not been explored. Here, we report a novel, rapid, effective hairy root transformation system. Compared to the in vitro cotyledon transformation method, this method shortened the time needed to obtain transgenic roots by 13 days. Furthermore, we combined this root transformation method with CRISPR/Cas9 technology and validated our system by exploring the expression and function of CsMYB36, a pivotal gene associated with root development and nutrient uptake. The hairy root transformation system established in this study provides a powerful method for rapidly identifying essential genes related to root development in cucumber and other horticultural crop species. This advancement holds promise for expediting research on root biology and molecular breeding strategies, contributing to the broader understanding and improvements crop growth and development.

Revisit and explore the ethylene-independent mechanism of sex expression in cucumber (Cucumis sativus)

KEY MESSAGE

This review provides a thorough and comprehensive perspective on the topic of cucumber sexual expression. Specifically, insights into sex expression mediated by pathways other than ethylene are highlighted. Cucumber (Cucumis sativus L.) is a common and important commercial crop that is cultivated and consumed worldwide. Additionally, this species is commonly used as a model for investigating plant sex expression. Cucumbers exhibit a variety of floral arrangements, comprising male, female, and hermaphroditic (bisexual) flowers. Generally, cucumber plants that produce female flowers are typically preferred due to their significant impact on the overall output. Various environmental conditions, such as temperature, light quality, and photoperiod, have been also shown to influence the sex expression in this species. Multiple lines of evidence indicate that ethylene and its biosynthesis genes are crucial in regulating cucumber sex expression. Gibberellins, another well-known phytohormone, can similarly influence cucumber sex expression via an ethylene-independent route. Further studies employing the next-generation sequencing technology also visualized a deeper slice of the molecular mechanism such as the role of the cell cycle program in the cucumber sex expression. This review aims to provide an overview of the sex expression of cucumber including its underlying molecular mechanism and regulatory aspects based on recent investigations.

Transcriptomic analysis reveals the molecular basis of photoperiod-regulated sex differentiation in tropical pumpkins (Cucurbita moschata Duch.)

BACKGROUND

Photoperiod, or the length of the day, has a significant impact on the flowering and sex differentiation of photoperiod-sensitive crops. The "miben" pumpkin (the main type of Cucurbita moschata Duch.) is well-known for its high yield and strong disease resistance. However, its cultivation has been limited due to its sensitivity to photoperiod. This sensitivity imposes challenges on its widespread cultivation and may result in suboptimal yields in regions with specific daylength conditions. As a consequence, efforts are being made to explore potential strategies or breeding techniques to enhance its adaptability to a broader range of photoperiods, thus unlocking its full cultivation potential and further promoting its valuable traits in agriculture.

RESULTS

This study aimed to identify photoperiod-insensitive germplasm exhibiting no difference in sex differentiation under different day-length conditions. The investigation involved a phenotypic analysis of photoperiod-sensitive (PPS) and photoperiod-insensitive (PPIS) pumpkin materials exposed to different day lengths, including long days (LDs) and short days (SDs). The results revealed that female flower differentiation was significantly inhibited in PPS_LD, while no differences were observed in the other three groups (PPS_SD, PPIS_LD, and PPIS_SD). Transcriptome analysis was carried out for these four groups to explore the main-effect genes of sex differentiation responsive to photoperiod. The main-effect gene subclusters were identified based on the principal component and hierarchical cluster analyses. Further, functional annotations and enrichment analysis revealed significant upregulation of photoreceptors (CmCRY1, F-box/kelch-repeat protein), circadian rhythm-related genes (CmGI, CmPRR9, etc.), and CONSTANS (CO) in PPS_LD. Conversely, a significant downregulation was observed in most Nuclear Factor Y (NF-Y) transcription factors. Regarding the gibberellic acid (GA) signal transduction pathway, positive regulators of GA signaling (CmSCL3, CmSCL13, and so forth) displayed higher expression levels, while the negative regulators of GA signaling, CmGAI, exhibited lower expression levels in PPS_LD. Notably, this effect was not observed in the synthetic pathway genes. Furthermore, genes associated with ethylene synthesis and signal transduction (CmACO3, CmACO1, CmERF118, CmERF118-like1,2, CmWIN1-like, and CmRAP2-7-like) showed significant downregulation.

CONCLUSIONS

This study offered a crucial theoretical and genetic basis for understanding how photoperiod influences the mechanism of female flower differentiation in pumpkins.

Genome-Wide Identification and Expression Analysis of the Cucumber FKBP Gene Family in Response to Abiotic and Biotic Stresses

The FKBP (FK506-binding protein) gene family is an important member of the PPlase protease family and plays a vital role during the processes of plant growth and development. However, no studies of the FKBP gene family have been reported in cucumber. In this study, 19 FKBP genes were identified in cucumber, which were located on chromosomes 1, 3, 4, 6, and 7. Phylogenetic analysis divided the cucumber FKBP genes into three subgroups. The FKBP genes in the same subgroup exhibited similar structures and conserved motifs. The cis-acting elements analysis revealed that the promoters of cucumber FKBP genes contained hormone-, stress-, and development-related cis-acting elements. Synteny analysis of the FKBP genes among cucumber, Arabidopsis, and rice showed that 12 kinds of syntenic relationships were detected between cucumber and Arabidopsis FKBP genes, and 3 kinds of syntenic relationships were observed between cucumber and rice FKBP genes. The tissue-specific expression analysis showed that some FKBP genes were expressed in all tissues, while others were only highly expressed in part of the 10 types of tissues. The expression profile analysis of cucumber FKBP genes under 13 types of stresses showed that the CsaV3_1G007080 gene was differentially expressed under abiotic stresses (high temperature, NaCl, silicon, and photoperiod) and biotic stresses (downy mildew, green mottle mosaic virus, Fusarium wilt, phytophthora capsica, angular leaf spot, and root-knot nematode), which indicated that the CsaV3_1G007080 gene plays an important role in the growth and development of cucumber. The interaction protein analysis showed that most of the proteins in the FKBP gene family interacted with each other. The results of this study will lay the foundation for further research on the molecular biological functions of the cucumber FKBP gene family.

Sex determination in papaya: Current status and perspectives

Papaya (Carica papaya L.) is an economically significant plant that produces fruit consumed worldwide due to its organoleptic characteristics. Since their commercial production, papaya fruits have faced several problems, such as pests, which have been partly resolved using transgenic varieties. Nevertheless, a principal challenge in this cultivation is the plant's sex determination. The sex issue in papaya is complex because papaya flowers can bear three sex forms: male, female, and hermaphrodite, which affects their fruit production, shape, and yield. Fruits from hermaphrodite plants are preferred more by consumers than female ones, and male plants rarely produce fruits without commercial value. Chromosomes are responsible for sex determination in papaya, denoted as XY for male, XX for female, and XYh for hermaphrodite. However, genes related to sex have been reported but are not conclusive. Factors such as the environment, hormones, and genetic and epigenetic background can also affect sex expression. Therefore, in this review, we will discuss recent research on the sex of papaya, from reported genes to date, their biology, and sexing approaches using molecular markers and their advantages.