A cold-tolerant evergreen interspecific hybrid of Ocimum kilimandscharicum and Ocimum basilicum: analyzing trichomes and molecular variations

Genetic linkage mapping and quantitative trait locus (QTL) analysis of sweet basil (Ocimum basilicum L.) to identify genomic regions associated with cold tolerance and major volatiles

Chilling sensitivity is one of the greatest challenges affecting the marketability and profitability of sweet basil (Ocimum basilicum L.) in the US and worldwide. Currently, there are no sweet basils commercially available with significant chilling tolerance and traditional aroma profiles. This study was conducted to identify quantitative trait loci (QTLs) responsible for chilling tolerance and aroma compounds in a biparental mapping population, including the Rutgers advanced breeding line that served as a chilling tolerant parent, 'CB15', the chilling sensitive parent, 'Rutgers Obsession DMR' and 200 F2 individuals. Chilling tolerance was assessed by percent necrosis using machine learning and aroma profiling was evaluated using gas chromatography (GC) mass spectrometry (MS). Single nucleotide polymorphism (SNP) markers were generated from genomic sequences derived from double digestion restriction-site associated DNA sequencing (ddRADseq) and converted to genotype data using a reference genome alignment. A genetic linkage map was constructed and five statistically significant QTLs were identified in response to chilling temperatures with possible interactions between QTLs. The QTL on LG24 (qCH24) demonstrated the largest effect for chilling response and was significant in all three replicates. No QTLs were identified for linalool, as the population did not segregate sufficiently to detect this trait. Two significant QTLs were identified for estragole (also known as methyl chavicol) with only qEST1 on LG1 being significant in the multiple-QTL model (MQM). QEUC26 was identified as a significant QTL for eucalyptol (also known as 1,8-cineole) on LG26. These QTLs may represent key mechanisms for chilling tolerance and aroma in basil, providing critical knowledge for future investigation of these phenotypic traits and molecular breeding.

Low-temperature perception and modulations in Ocimum basilicum commercial cultivar CIM-Shishir: Biosynthetic potential with insight towards climate-smart resilience

The newly released interspecific hybrid variety CIM-Shishir, resulting from a cross between Ocimum basilicum and Ocimum kilimandscharicum claims to be a multicut, lodging resistant, cold tolerant, high essential oil yielding with linalool rich variety. It has a purple-green stem and has a unique feature and advantage of better survival in the winter season than other O. basilicum varieties, illustrating its physiological mechanisms for cold tolerance. In this study, we subjected both the CIM-Shishir variety and a control plant to cold stress to investigate the impact of low temperatures on various physiological, trichome developments, secondary metabolite constitution aspects related to essential oil production, and gene expression. The analysis revealed a significantly higher density and altered morphology of trichomes on the leaf surface of the variety subjected to low temperatures, indicating its adaptation to cold conditions. Furthermore, when comparing the treated plants under low-temperature stress, it was observed that the relative electrolyte leakage and Malondialdehyde (MDA) contents substantially increased in the control in contrast to the CIM-Shishir variety. This finding suggests that CIM-Shishir exhibits superior cold tolerance. Additionally, an increase in proline content was noted in the variety exposed to low temperatures compared to the control. Moreover, the chlorophyll and anthocyanin content gradually increased with prolonged exposure to low-temperature stress in the newly developed variety, indicating its ability to maintain photosynthetic capacity and adapt to cold conditions. The activities of superoxide dismutase (SOD) also increased under low-temperature conditions in the CIM-Shishir variety, further highlighting its cold tolerance behaviour. In our research, we investigated the comprehensive molecular mechanisms of cold response in Ocimum. We analyzed the expression of key genes associated with cold tolerance in two plant groups: the newly developed hybrid variety known as CIM-Shishir Ocimum, which exhibits cold tolerance, and the control plants susceptible to cold climates that include WRKY53, ICE1, HOS1, COR47, LOS15, DREB5, CBF4, LTI6, KIN, and ERD2. These genes exhibited significantly higher expression levels in the CIM-Shishir variety compared to the control, shedding light on the genetic basis of its cold tolerance. The need for climate-smart, resilient high-yielding genotype is of high importance due to varied climatic conditions as this will hit the yield drastically and further to the economic sectors including farmers and many industries that are dependent on the bioactive constituents of Ocimum.

Formation mechanism of glandular trichomes involved in the synthesis and storage of terpenoids in lavender

BACKGROUND

Lavender (genus Lavandula, family Lamiaceae) is an aromatic plant widely grown as an ornamental plant. The chemical composition of lavender is characterized by monoterpenoids, sesquiterpenoids, and other compounds, which are primarily synthesized and stored in epidermal secretory structures called glandular trichomes (GTs). Volatile organic compounds (VOCs) are responsible for the aroma characteristics of plant oil that drive consumer preference. Aroma is usually regarded as a characteristic trait for the classification of aromatic plants. Interestingly, VOCs are synthesized and stored in GTs. Lamiaceae species such as purple perilla, peppermint, basil, thyme, and oregano usually possess two types of GTs: peltate glandular trichomes (PGTs) and capitate glandular trichomes (CGTs). But the development process of PGTs in lavender has been reported in only a few studies to date.

RESULTS

In this study, we identified and quantified the VOCs in four lavender cultivars by headspace-solid phase micro extraction-gas chromatography mass spectrometry (HS-SPME-GC-MS). A total of 66 VOCs were identified in these four cultivars, the most prominent of which were linalyl acetate and linalool, and flowers were the main site of accumulation of these VOCs. Here, we examined the developmental process of PGTs, including the formation of their base, body, and apex. The apex cells contained secretory cavities, which produced VOCs. Based on the reference genome sequence of the lavender cultivar 'Jingxun 2', several R2R3-MYB subfamily genes related to GT formation were identified. These results will guide the engineering of GTs and molecular breeding of lavender for improving the VOC content.

CONCLUSIONS

In this study, we identified the VOCs in four lavender cultivars. We analyzed the formation of GTs, and compared the number and diameter size of PGTs among four lavender cultivars. Additionally, we identified four candidate genes belonging to the R2R3-MYB family.

DNA Fingerprinting and Genetic Relationships Similarities Among the Accessions/Species of Ocimum Using SCoT and ISSR Markers System

Studies on genetic diversity could enhance taxonomic authentication and evolutionary relationship among the species of Ocimum. Therefore, diversity among 36 Ocimum accessions representing species from different regions of world were analyzed using Start Codon-Targeted Polymorphism (SCoT) and inter-simple sequences repeat (ISSR) marker. Marker systems used in this study was potentially targeted the different regions of the genome and included 18 SCoT and 15 ISSR primers, which showed successful amplification profile for Ocimum. Between these two, SCoT revealed the highest mean value of percentage of Polymorphism (84.6%), polymorphic information content (PIC, 0.65), and resolving power (Rp, 8.80), which were higher than ISSR. A total of 140 and 111 amplicons were obtained with SCoT and ISSR marker. The Mantel test indicted a significant correlation (r² = 0.44) between ISSR and SCoT, which suggested a common genetical background among the accessions. The principal coordinate study showed the selection of different Ocimum genotypes by the cluster analysis. This study will help and support identification, genetic mapping, and molecular ecology to enhance the breeding program's efficiency for developing elite varieties to meet industrial demand globally. The present study is the first report of the genetic diversity, and relationship determination with SCoT-based molecular marker among Ocimum accessions.

Epicormic bud protection traits vary along a latitudinal gradient in a neotropical savanna

Regrowth via production of epicormic shoots is an important strategy for many woody plants after environmental disturbances such as fire, drought, and herbivory. Populations spreading across a broad latitudinal gradient offer opportunities to investigate if essential traits vary with heterogenous environmental conditions, such as in savanna ecosystems. This information can help us predict plant responses to climate change. Here, we evaluated if epicormic bud protection traits varied among populations of three focal savanna species (Miconia albicans, Solanum lycocarpum, and Zeyheria montana) that have a wide distribution and grow under variable climatic conditions. We randomly sampled 225 individuals over five spatially independent sites (7°, 10°, 15°, 18°, and 24° S) in Brazil, totaling 15 individuals per species per area. We analyzed anatomical transverse sections of five buds per species per area to assess the relative area occupied by crystal and phenolic idioblasts, the thickness of the trichome boundary layer, and to test if these traits were associated with climatic conditions. The buds were protected by cataphylls and composed of a variable number of undeveloped leaves enveloping the shoot apex. For M. albicans, we found an association between maximum temperature and both phenolic idioblasts and trichome boundary layer, but no association with crystal idioblasts. In S. lycocarpum, only the trichome boundary layer was associated with maximum temperature plus high radiation. Z. montana showed no variation. Combination of two or more traits can lead to the development of adaptative strategies to different climatic conditions. We present for the first time an analysis of epicormic bud traits in plant populations occurring in an extensive latitudinal gradient and shed light on how maximum temperature is associated with these traits, contributing to a better understanding of plant resprouting capabilities in widespread savanna plant species.

Morpho-Physiological and Genomic Evaluation of Juglans Species Reveals Regional Maladaptation to Cold Stress

Climate change may have unpredictable effects on the cold hardiness of woody species planted outside of their range of origin. Extreme undulations in temperatures may exacerbate susceptibility to cold stress, thereby interfering with productivity and ecosystem functioning. Juglans L. and their naturally occurring interspecific F1 hybrids, are distributed natively across many temperate regions, and J. regia has been extensively introduced. Cold hardiness, an environmental and genetic factor yet to be evaluated in many native and introduced Juglans species, may be a limiting factor under future climate change and following species introductions. We evaluated cold hardiness of native North American and Eastern Asian Juglans along with J. regia genotypes using field data from the Midwestern United States (Indiana), controlled freezing tests, and genome sequencing with close assessment of Juglans cold hardy genes. Many Juglans species previously screened for cold-hardiness were genotypes derived from the Midwest, California, and Europe. In 2014, despite general climate adaptation, Midwestern winter temperatures of -30°C killed J. regia originating from California; however, naturalized Midwestern J. regia survived and displayed low damage. Hybridization of J. regia with black walnut (J. nigra) and butternut (J. cinerea) produced F1s displaying greater cold tolerance than pure J. regia. Cold hardiness and growth are variable in Midwestern J. regia compared to native Juglans, East Asian Juglans, and F1 hybrids. Phylogeny analyses revealed that J. cinerea sorted with East Asian species using the nuclear genome but with North American species using the organellar genome. Investigation of selected cold hardy genes revealed that J. regia was distinct from other species and exhibited less genetic diversity than native Juglans species Average whole genome heterozygosity and Tajima's D for cold hardy genes was low within J. regia samples and significantly higher for hybrid as well as J. nigra. We confirmed that molecular and morpho-physiological data were highly correlated and thus can be used effectively to characterize cold hardiness in Juglans species. We conclude that the genetic diversity within local J. regia populations is low and additional germplasm is needed for development of more regionally adapted J. regia varieties.

Ocimum basilicum (Basil) Modulates Apoptosis and Neurogenesis in Olfactory Pulp of Mice Exposed to Chronic Unpredictable Mild Stress

BACKGROUND

Ocimum basilicum (O. basilicum) was described to have antidepressant and anxiolytic activities. Although the relationship between the main olfactory bulb (MOB) and depression was recently reported, the chronic stress-induced dysfunction of the MOB is not clearly described.

OBJECTIVES

This study aimed to assess the efficacy of inhalation of O. basilicum essential oils in improving chronic unpredictable mild stress (CUMS)-induced changes in MOB of mice and understand the mechanism underlying such effect.

MATERIALS AND METHODS

Adult male mice (n=40) were assigned into four groups included the control, CUMS-exposed, CUMS + fluoxetine (FLU), CUMS + O. basilicum. Behavioral changes, serum corticosterone level, and gene expression of GFAP, Ki 67, and caspase-3 were assessed using real-time PCR (RT-PCR). Histopathological and immunochemical examination of the MOB was performed.

RESULTS

FLU and O. basilicum significantly down-regulated (p = 0.002, p<0.001) caspase-3 gene expression indicating reduced apoptosis and up-regulated (p = 0.002, p < 0.001) Ki67 gene expression indicating enhanced neurogenesis in MOB, respectively. FLU and O. basilicum-treated mice markedly improved MOB mitral cell layer distortion and shrinkage induced by CUMS.

CONCLUSION

O. basilicum relieved both biochemically and histopathological chronic stress-induced changes in the main olfactory bulb possibly through up-regulation of gene expression of GFAP and Ki67 and down-regulation of caspase-3 in the MOB.

Interspecies comparative features of trichomes in Ocimum reveal insights for biosynthesis of specialized essential oil metabolites

Ocimum species commonly referred to as "Tulsi" are well-known for their distinct medicinal and aromatic properties. The characteristic aroma of Ocimum species and cultivars is attributed to their specific combination of volatile phytochemicals mainly belonging to terpenoid and/or phenylpropanoid classes in their essential oils. The essential oil constituents are synthesized and sequestered in specialized epidermal secretory structures called as glandular trichomes. In this comparative study, inter- and intra-species diversity in structural attributes and profiles of expression of selected genes related to terpenoid and phenylpropanoid biosynthetic pathways have been investigated. This is performed to seek relationship of variations in the yield and phytochemical composition of the essential oils. Microscopic analysis of trichomes of O. basilicum, O. gratissimum, O. kilimandscharicum, and O. tenuiflorum (green and purple cultivars) revealed substantial variations in density, size, and relative proportions of peltate and capitate trichomes among them. The essential oil yield has been observed to be controlled by the population, dominance, and size of peltate and capitate glandular trichomes. The essential oil sequestration in leaf is controlled by the dominance of peltate glandular trichome size over its number and is also affected by the capitate glandular trichome size/number with variations in leaf area albeit at lower proportions. Comprehension and comparison of results of GC-MS analysis of essential oils showed that most of the Ocimum (O. basilicum, O. tenuiflorum, and O. gratissimum) species produce phenylpropanoids (eugenol, methyl chavicol) as major volatiles except O. kilimandscharicum, which is discrete in being monoterpenoid-rich species. Among the phenylpropanoid-enriched Ocimum (O. basilicum, O. gratissimum, O. tenuiflorum purple, O. tenuiflorum green) as well, terpenoids were important constituents in imparting characteristic aroma. Further, comparative abundance of transcripts of key genes of phenylpropanoid (PAL, C4H, 4CL, CAD, COMT, and ES) and terpenoid (DXS and HMGR) biosynthetic pathways was evaluated vis-à-vis volatile oil constituents. Transcript abundance demonstrated that richness of their essential oils with specific constituent(s) of a chemical group/subgroup was manifested by the predominant upregulation of phenylpropanoid/terpenoid pathway genes. The study provides trichomes as well as biosynthetic pathway-based knowledge for genetic improvement in Ocimum species for essential oil yield and quality.

Biochemical characterization and spatio-temporal analysis of the putative L-DOPA pathway in Mucuna pruriens

Transcriptome analysis and biochemical characterization of the putative l-3,4-dihydroxyphenylalanine (l-DOPA) pathway in Mucuna pruriens (L.) DC have been performed. Spatio-temporal quantification of the putative l-DOPA biosynthetic pathway genes and its correlation with respective metabolites was established. l-tyrosine, l-DOPA, and dopamine from all plant parts were quantified. The de novo transcriptome analysis was performed using leaves of the selected M. pruriens mutant T-IV-9 during maturity. The putative L-DOPA pathway and its regulatory genes were retrieved from transcriptome data and the L-DOPA pathway was biochemically characterized. The spatial and temporal gene expression for the L-DOPA pathway was identified with respect to the chemical constituents. L-tyrosine, L-DOPA, and dopamine contents were highest in leaves during maturity (about 170-day-old plants). The polyphenol oxidase (PPO) was highly expressed in tender stems (230-fold higher as compared to seeds) as well as a high L-DOPA content. The PPO gene was highly expressed in leaves (3367.93 in FPKM) with a 79-fold increase compared to control plants during maturity. L-DOPA was found in every part with varied levels. The highest L-DOPA content was found in mature dried seed (3.18-5.8%), whereas the lowest amount was recorded in mature and dried leaves. The reproductive parts of the plant had a higher amount of L-DOPA content (0.9-5.8%) compared to the vegetative parts (0.2-0.91%). Various amino acid transporters and permeases were expressed in M. pruriens. The transcripts of dopa decarboxylase (DDC) were found in almost all parts of the plant, but its higher content was limited to the leaf.

Comparative transcriptome study of hairy and hairless tea plant (Camellia sinensis) shoots

Trichome (also referred to as 'háo' in tea) is a key feature in both tea products and tea plant (Camellia sinensis) selection breeding. Although trichomes are used as a model for studying cell differentiation and have been well studied in many plant species, the regulation of trichome formation at the molecular level is poorly understood in tea plants. In the present study, the hairy and hairless tea plant cultivars Fudingdabaicha (FDDB) and Rongchunzao (RCZ), respectively, were used to study this mechanism. We characterised tea plant trichomes as unicellular and unbranched structures. High-throughput Illumina sequencing yielded approximately 277.0 million high-quality clean reads from the FDDB and RCZ cultivars. After de novo assembly, 161,444 unigenes were generated, with an average length of 937 bp. Among these unigenes, 81,425 were annotated using public databases, and 55,201 coding sequences and 4004 transcription factors (TFs) were identified. In total, 21,599 differentially expressed genes (DEGs) were identified between RCZ and FDDB, of which 10,785 DEGs were up-regulated and 10,814 DEGs were down-regulated. Genes involved in the DNA replication pathway were significantly enriched. Furthermore, between FDDB and RCZ, DEGs related to TFs, phytohormone signals, and cellulose synthesis were identified, suggesting that certain genes involved in these pathways are crucial for trichome initiation in tea plants. Together, the results of this study provide novel data to improve our understanding of the potential molecular mechanisms of trichome formation and lay a foundation for additional trichome studies in tea plants.

Analyzing trichomes and spatio-temporal expression of a cysteine protease gene Mucunain in Mucuna pruriens L. (DC)

Mucuna pruriens is a well-known legume for the itching attributes of the trichome and a valuable medicinal herb that is used for the treatment of Parkinson's disease, sexual debilities, etc. Its cultivation was deprived due to its itching behavior. The wild genotype of M. pruriens have the largest trichome length (2015 ± 29 μm) compared to other genotype and mutants. The white-seeded variety of M. pruriens was found to be the most suitable for large-scale cultivation due to the small trichome size and less trichome density on the pod. The external surface trichomes have protuberance with unknown function. The unicellular trichomes of Mucuna show the flowing fluid or cytoplasm inside the trichome. The unigenes regulating the differentiation and development of the trichome such as GLABRA-1, GLABRA-2, and cpr-5 have been identified in M. pruriens transcriptome of the leaf. The Mucunain shows a higher transcript abundance in the flower and pod cover compared to the seeds. The Mucunain was found in every stage of plant growth, but it was highly expressed during maturity (about 170 days) with a high fragment per kilobase per million value.

Ocimum Genome Sequencing—A Futuristic Therapeutic Mine

Next-generation sequencing (NGS) platforms from the past decade are in the continuous efforts of changing the impact of sequencing on our current knowledge about plant genes, genomes, and their regulation. Holy basil (Ocimum tenuiflorum L. or sanctum L.) genome sequencing has also paved the path for deeper exploration of the medicinal properties of this beneficial herb making it a true ‘elixir of life.’ The draft genome sequence of the holy basil has not only opened the avenues for the drug discovery but has also widened the prospects of the molecular breeding for development of new improved plant varieties.

Inducing mutations through γ-irradiation in seeds of Mucuna pruriens for developing high L-DOPA-yielding genotypes

PURPOSE

To develop elite genotypes in Mucuna pruriens (L.) DC with high L-DOPA (L-3, 4 dihydroxyphenylalanine) yields, with non-itching characteristics and better adaptability by applying γ-irradiation. Molecular and chemical analysis was performed for screening based on specific characteristics desired for developing suitable genotypes.

MATERIALS AND METHODS

Developed, mutant populations were analyzed for L-DOPA % in seeds through TLC (thin layer chromatography), and the results obtained were validated with the HPLC (High performance liquid chromatography). The DNA (Deoxyribonucleic acid) was isolated from the leaf at the initial stage and used for DNA polymorphism. RNA (Ribonucleic acid) was isolated from the leaf during maturity and used for expression analysis.

RESULTS

The selected mutant T-I-7 showed 5.7% L-DOPA content compared to 3.18% of parent CIM-Ajar. The total polymorphism obtained was 57% with the molecular marker analysis. The gene expression analysis showed higher fold change expression of the dopadecarboxylase gene (DDC) in control compared to selected mutants (T-I-7, T-II-23, T-IV-9, T-VI-1).

CONCLUSION

DNA polymorphism was used for the screening of mutants for efficient screening at an early stage. TLC was found suitable for the large-scale comparative chemical analysis of L-DOPA. The expression profile of DDC clearly demonstrated the higher yields of L-DOPA in selected mutants developed by γ-irradiation in the seeds of the control.