NbJAZ3 is required for jasmonate-meditated glandular trichome development in Nicotiana benthamiana

NtHD9 modulates plant salt tolerance by regulating the formation of glandular trichome heads in Nicotiana tabacum

Salt stress is one of the main abiotic factor affecting plant growth. We have previously identified a key gene (NtHD9) in Nicotiana tabacum L. that positively regulates the formation of long glandular trichomes (LGTs). Here, we verified that both abiotic stress (aphids, drought and salt stress) could restore the phenotype lacking LGTs in NtHD9-knockout (NtHD9-KO) plants. The abiotic stress response assays indicated that NtHD9 is highly sensitive to salt stress. Compared with cultivated tobacco "K326" (CK) plants, NtHD9-overexpressing (NtHD9-OE) plants with more LGTs exhibited stronger salt tolerance, whereas NtHD9-KO with no LGTs showed weaker tolerance to salt. The densities and sizes of the glandular heads gradually increased with increasing NaCl concentrations in NtHD9-KO plants. Mineral element determination showed that leaves and trichomes of NtHD9-OE plants accumulated less Na+ but had higher K+ contents under salt stress, thus maintaining ion homeostasis in plants, which could contribute to a robust photosynthetic and antioxidant system under salt stress. Therefore, NtHD9-OE plants maintained a larger leaf area and root length under high-salt conditions than CK and NtHD9-KO plants. We verified that NtHD9 could individually interact with NtHD5, NtHD7, NtHD12, and NtJAZ10 proteins. Salt stress led to an increase in jasmonic acid (JA) levels and activated the expression of NtHDs while inhibiting the expression of NtJAZ. This study suggests that the glandular heads play an important role in plant resistance to salt stress. The activation of JA signaling leading to JAZ protein degradation may be key factors regulating the glandular heads development under salt stress.

Safe Farming: Ultrafine Bubble Water Reduces Insect Infestation and Improves Melon Yield and Quality

Melon pest management relies on the excessive application of pesticides. Reducing pesticide spraying has become a global issue for environmental sustainability and human health. Therefore, developing a new cropping system that is sustainable and eco-friendly is important. This study found that melon seedlings irrigated with ultrafine water containing H2 and O2 (UFW) produced more root hairs, increased shoot height, and produced more flowers than the control irrigated with reverse osmosis (RO) water. Surprisingly, we also discovered that UFW irrigation significantly reduced aphid infestation in melons. Based on cryo-scanning electron microscope (cryo-SEM) observations, UFW treatment enhanced trichome development and prevented aphid infestation. To investigate whether it was H2 or O2 that helped to deter insect infestation, we prepared UF water enrichment of H2 (UF+H2) and O2 (UF+O2) separately and irrigated melons. Cryo-SEM results indicated that both UF+H2 and UF+O2 can increase the density of trichomes in melon leaves and petioles. RT-qPCR showed that UF+H2 significantly increased the gene expression level of the trichome-related gene GLABRA2 (GL2). We planted melons in a plastic greenhouse and irrigated them with ultrafine water enrichment of hydrogen (UF+H2) and oxygen (UF+O2). The SPAD value, photosynthetic parameters, root weight, fruit weight, and fruit sweetness were all better than the control without ultrafine water irrigation. UFW significantly increased trichome development, enhanced insect resistance, and improved fruit traits. This system thus provides useful water management for pest control and sustainable agricultural production.

Metabolic engineering of a 1,8-cineole synthase enhances aphid repellence and increases trichome density in transgenic tobacco (Nicotiana tabacum L.)

BACKGROUND

The green peach aphid (Myzus persicae Sulzer) is a harmful agricultural pest that causes severe crop damage by directly feeding or indirectly vectoring viruses. 1,8-cineole synthase (CINS) is a multiproduct enzyme that synthesizes monoterpenes, with 1,8-cineole dominating the volatile organic compound profile. However, the relationship between aphid preference and CINS remains elusive.

RESULTS

Here, we present evidence that SoCINS, a protein from garden sage (Salvia officinalis), enhanced aphid repellence and increased trichome density in transgenic tobacco. Our results demonstrated that overexpression of SoCINS (SoCINS-OE) led to the emission of 1,8-cineole at a level of up to 181.5 ng per g fresh leaf. Subcellular localization assay showed that SoCINS localized to chloroplasts. A Y-tube olfactometer assay and free-choice assays revealed that SoCINS-OE plants had a repellent effect on aphids, without incurring developmental or fecundity-related penalties. Intriguingly, the SoCINS-OE plants displayed an altered trichome morphology, showing increases in trichome density and in the relative proportion of glandular trichomes, as well as enlarged glandular cells. We also found that SoCINS-OE plants had significantly higher jasmonic acid (JA) levels than wild-type plants. Furthermore, application of 1,8-cineole elicited increased JA content and trichome density.

CONCLUSION

Our results demonstrate that SoCINS-OE plants have a repellent effect on aphids, and suggest an apparent link between 1,8-cineole, JA and trichome density. This study presents a viable and sustainable approach for aphid management by engineering the expression of 1,8-cineole synthase gene in plants, and underscores the potential usefulness of monoterpene synthase for pest control. © 2023 Society of Chemical Industry.

Hormonal control of promoter activities of Cannabis sativa prenyltransferase 1 and 4 and salicylic acid mediated regulation of cannabinoid biosynthesis

Cannabis sativa aromatic prenyltransferase 4 (CsPT4) and 1 (CsPT1) have been shown to catalyze cannabigerolic acid (CBGA) biosynthesis, a step that rate-limits the cannabinoid biosynthetic pathway; both genes are highly expressed in flowers. CsPT4 and CsPT1 promoter driven β-glucuronidase (GUS) activities were detected in leaves of cannabis seedlings, and strong CsPT4 promoter activities were associated with glandular trichomes. Hormonal regulation of cannabinoid biosynthetic genes is poorly understood. An in silico analysis of the promoters identified putative hormone responsive elements. Our work examines hormone-responsive elements in the promoters of CsPT4 and CsPT1 in the context of physiological responses of the pathway to the hormone in planta. Dual luciferase assays confirmed the regulation of promoter activities by the hormones. Further studies with salicylic acid (SA) demonstrated that SA pretreatment increased the expression of genes located downstream of the cannabinoid biosynthetic pathway. The results from all aspects of this study demonstrated an interaction between certain hormones and cannabinoid synthesis. The work provides information relevant to plant biology, as we present evidence demonstrating correlations between molecular mechanisms that regulate gene expression and influence plant chemotypes.

Transcription factors NtHD9 and NtHD12 control long glandular trichome formation via jasmonate signaling

Glandular trichomes are universal epidermal structures that produce abundant specialized metabolites. However, knowledge of the initiation of glandular heads in glandular trichomes is limited. Herein, we found an intrinsic link of morphogenesis between glandular trichomes and non-glandular trichomes. Two novel homeodomain leucine zipper II members in tobacco (Nicotiana tabacum), NtHD9 and NtHD12, played important roles in long glandular trichome formation: NtHD9 was responsible for glandular head formation, while NtHD12 simultaneously controlled the formation of stalks and glandular heads. DAP-seq analysis suggested that NtHD9 can bind to the KKGCATTWAWTR motif of the cytochromes P450 94C1 (NtCYP94C1) promoter, which is involved in jasmonoyl-isoleucine oxidation. RNA-seq analysis of non-transformed tobacco and nthd9 plants revealed that NtHD9 modulates the expression of jasmonate (JA) signaling- and six trichome development-related genes. Notably, MeJA treatment restored the morphogenesis of long glandular trichomes in nthd9 and nthd12 plants, and the size of glandular heads increased with increasing MeJA concentration. However, the phenotype of long glandular trichome absence in double mutants of NtHD9 and NtHD12 could not be restored by MeJA. Our data demonstrate that NtHD9 and NtHD12 have distinct major functions yet overlapping roles in long glandular trichome formation via JA signaling.