Exploring research trends and priorities of genus Melia

The genus Melia is known for its secondary metabolites and recently, this genus is being explored for its timber. There are vast differences among its species. For instance, Melia azedarach is reported to be invasive and while another species, M. dubia, has diverse utility with complex germination and regeneration characteristics. Researchers globally have been working on various aspects of this genus; In this study, using topic modelling and science mapping approach, we attempted to understand research facets on this genus. The literature corpus of the Web of Science database was explored using a single keyword-"Melia" which yielded 1523 publications (1946-2022) and after scrutiny metadata of 1263 publications were used in the study. Although nine individual species were cited in the publications, only three species are accepted viz., M. dubia, M. azedarach, and M. volkensii. This implies taxonomic uncertainty, with potential confusion in assigning scientific findings to particular species. Thus, a taxonomic relook on this genus is warranted for a better assessment of the economic utility in many countries. More importantly, our results indicate that the research interests have recently shifted from the secondary metabolite constituents towards growth, biomass, wood properties, germination, plantation, and green synthesis. The shift in research focus toward wood properties of Melia sp. can impact the wood demand-supply at a global scale owing to its fast growth and the possibility of cultivation over a wider geographical range.

Diaporthe phaseolorum causing dieback disease on Melia dubia cav. in Karnataka state (India)

Melia dubia is an important tree species grown worldwide for its medicinal and timber values. It is widely used in timber and pulp industry and also as an organic pesticide, fertilisers, agro-forestry and herbal formulations. During 2019-2022, a dieback disease in plantations of M. dubia was recorded in Mysore, Mandya, Chamarajanagar, Hassan and Tumkur districts of Karnataka state (India) with disease incidence of 26.25%. The associated pathogen was isolated on PDA medium and its morpho-cultural characteristics were studied. The genomic DNA of the pathogen was isolated, and rDNA was amplified and sequenced using universal primers. Based on the microscopic, morpho-cultural, sequence data and phylogenetic analysis, the pathogen was identified as Diaporthe phaseolorum (Cooke & Ellis) Sacc. Koch's postulates were performed both in vitro and in vivo and the typical symptoms of dieback disease were recorded on post-inoculated saplings. The dieback disease is responsible for the poor growth of Melia species in the region, and hence, there is an urgent need to manage the disease in plantations using integrated management practices. This is the first report of the occurrence of D. phaseolorum on M. dubia plantations in India.

Differential gene expression analysis reveals the fast-growth mechanisms in Melia dubia at different stand ages

BACKGROUND

Melia dubia Cav. is a fast-growing multipurpose tree suitable for agroforestry and has been widely cultivated for wood-based industries, particularly pulp and paper production. Despite its high economic value in India, there is a lack of information regarding the molecular mechanism driving its fast-growth. Therefore, this study aimed to elucidate the molecular mechanisms responsible for fast-growth by expression analysis of selective candidate genes.

METHODS AND RESULTS

Initially, growth traits were assessed, including tree height and diameter at breast height (DBH), across three different ages (one-year-old, two-year-old, and three-year-old) of M. dubia plantations. Tree volume based on tree height and DBH, was also calculated. The analysis of annual tree height increment revealed that the second-year plantation exhibited the higher increment, followed by first and third years. In contrast, DBH was maximum in third-year plantation, followed by the second and first years. Similarly, annual tree volume increment showed a similar trend with DBH that maximum in the third year, followed by second and first years. Furthermore, a differential gene expression analysis was performed using qRT-PCR on four genes such as Phloem Intercalated with Xylem (PXY), Clavata3/Embryo Surrounding Region-Related 41 (CLE41), 1-aminocyclopropane-1-carboxylic acid synthase (ACS-1) and Hemoglobin1 (Hb1) for downstream analysis. The relative gene expression showed up-regulation of CLE41, ACS-1, and Hb1 genes, while the PXY gene was downregulated across the tree ages. Interestingly, a positive association was observed between tree growth and the expression of the selected candidate genes.

CONCLUSION

Our results pave the way for further research on the regulatory mechanisms of genes involved in fast-growth and provide a basis for genetic improvement of Melia dubia.

MS diagnostic model and rapid distinguishing of bioactive limonoids in fruits of Melia toosendan using solid-phase extraction coupled with LC-MS/MS

INTRODUCTION

Melia toosendan Sieb. et Zucc. has been used as a Chinese folk medicine for roundworm treatment since ancient times. Many diverse limonoids have been isolated from Meliaceae plants, but it remains difficult to isolate and identify other limonoids because of their small natural concentrations.

OBJECTIVE

This study was performed to overcome the difficulties associated with fast and accurate identification of limonoids and establish a reliable and sensitive method for the analysis of minor limonoids in M. toosendan fruits.

METHODS

An efficient strategy for enrichment, detection, and identification of minor limonoids from M. toosendan fruits using solid-phase extraction with high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (SPE-HPLC-Q-TOF-MS/MS) was developed herein.

RESULTS

Characteristic fragmentations and fragmentation ions containing trichilin-, nimbin-, and vilasinin-class limonoid skeletons were initially studied, and characteristic diagnostic ions involved retro Diels-Alder (RDA) reactions or homolytic cleavages, which were used to identify minor limonoids. In total, 13 limonoids, including four new ones, were identified.

CONCLUSION

This is the first report on the analysis of M. toosendan fruits to identify limonoids. This novel analysis method may stimulate further research regarding the identification of limonoids in other plant species.

Characterization of a 2,3-oxidosqualene cyclase in the toosendanin biosynthetic pathway of Melia toosendan

Toosendanin, bearing a furan ring, is a limonoid belonging to the group of tetranortriterpenoids. Toosendanin is a phytochemical found in the medicinal plant Melia toosendan Sieb. et Zucc. of the Meliaceae family. Toosendanin and its derivatives demonstrate high insecticidal activity and are important pesticides derived from plants. Despite intensive investigation of limonoids over several decades, the biosynthetic pathway of these triterpenoids is less understood. To identify the key enzymes involved in the toosendanin biosynthetic pathway, we analyzed the contents of toosendanin in various plant tissues and parts and found that the highest level of toosendanin was found in the developing fruit and gradually decreased as the fruit matured. More than 346 116 transcripts were assembled based on 394 million paired-end Illumina reads and 6 million PacBio reads from the pooled RNA samples of fruits, leaves and young barks. A total of 186 263 genes were predicted. Six 2,3-oxidosqualene cyclase (OSC) genes were identified by analyzing the association between gene expression and metabolite profiles. Functional analyses using the Nicotiana benthamiana transient expression assay showed that MtOSC1 catalyzed 2,3-oxidosqualene to produce a tetracyclic triterpene skeleton, tirucalla-7,24-dien-3β-ol, which is predicted as the precursor for toosendanin biosynthesis. We identified another OSC, MtOSC6, which is a lupeol synthase. Using synthetic biology methods, these identified enzymes could be used to model a biosynthetic pathway to produce large quantities of toosendanin.

Anti-amyloidogenic effects of ID1201, the ethanolic extract of the fruits of Melia toosendan, through activation of the phosphatidylinositol 3-kinase/Akt pathway

Amyloid beta (Aβ) peptides, which are generated from amyloid precursor protein (APP), are thought to play a major role in the pathogenesis of Alzheimer's disease (AD). This study investigated the anti-amyloidogenic effects of the ethanolic extract of Meliae Fructus (ID1201) using human embryonic kidney 293 cells with stably expressed human wild-type or Swedish mutant APP695 and β-secretase 1. ID1201 treatment enhanced the non-amyloidogenic metabolism of APP; increases in soluble APPα levels and decreases in soluble APPβ and Aβ levels resulted from the α-secretase activation through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. In addition, ID1201-treated 5×familial AD (FAD) mice with 5 mutations in APP and presenilin 1 showed reduced levels of Aβ and amyloid plaques in the brain relative to those of 5×FAD mice with vehicle treatments. These results indicate that ID1201 possesses anti-amyloidogenic effects via the activation of the PI3K/Akt pathway, suggesting that it is a potential therapeutic agent for AD.

Impact of botanical extracts derived from leaf extracts Melia azedarach L. (Meliaceae) and Amaranthus viridis L. (Amaranthaceae) on populations of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) and detoxification enzyme activities

Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), an important insect pest of many field crops, has developed resistance to various insecticides, making its control increasingly difficult. This study explored the effects of senescent Leaf Melia azedarach L. (Meliaceae) and Amaranthus viridis L. (Amaranthaeae) extract on second instar S. exigua Larvae survival by the dipping method. We also analyzed detoxification enzyme activities of carboxylesterase and gLutathione-s-transferase in in vitro tests with extract-treated insects. The leaf extract showed strong insecticide activity with a LC50 value of 9.793 mg/ml (r2 = 0.965) and 50.5702 mg/mi (r2 = 0.95) at 24 after exposure for M. azedarach L. and A. viridis L. extract, respectivrly but no significant increase in toxicity over time. The M. azedarach L. extract strongly inhibited all enzyme activities. In contrast with A. viridis L. extract, they inhibit only glutathione-s-transferase. This is the first report of highly effective insecticidal activity of the senescent leaf extract of A. viridis and M. azedarach L. against S. exigua. Both plant materials are a less expensive (0.5 $US per 1 kg leaf), suggesting this extract is a promising alternative tool for the management of this pest.

Antifungal synergistic effect of scopoletin, a hydroxycoumarin isolated from Melia azedarach L. fruits

In the continuous search for antifungal compounds from plants, the hydroxycoumarin scopoletin (1) was isolated from seed kernels of Melia azedarach L. from which three other compounds, vanillin (2), 4-hydroxy-3-methoxycinnamaldehyde (3), and (+/-) pinoresinol (4), have also been isolated. Guided fractionation through autobiography on TLC using Fusarium verticillioides (Saccardo) Nirenberg as test organism led to the isolation of 1, which exhibited a minimum inhibitory concentration (MIC) of 1.50 mg/mL in the microbroth dilution method. Despite its own weak activity, when the coumarin was combined with the above-mentioned compounds, a strong enhancement of the antifungal effect was observed, even showing a complete inhibition in the growth of the pathogen when 1 was added at a concentration of up to 5% of its MIC value. The same level of effectiveness was observed when the synthetic antifungal agents Mancozeb and Carboxin were each combined with compounds 1-4, in which cases it became possible to decrease the effective concentrations of these commercial compounds by up to 2.5 and 3%, respectively.