Biology subjects

Hassan Muralidhar, S.

Publications and source records attributed to Hassan Muralidhar, S..

3 recordsLinked to original sources

bioRxiv2026

Pathogen-induced red pigmentation uncovers a conserved floral defense in Asteraceae

Flower colour is predominantly selected for visual appeal and pollinator-driven evolution, however its role in plant-pathogen interaction remains unclear. Here, we investigated the relationship between anthocyanin accumulation and resistance to the necrotrophic pathogen Botrytis cinerea in Chrysanthemum morifolium. Using a unique set of spontaneous colour mutants sharing a common genetic background, we demonstrate that higher anthocyanin levels are associated with enhanced resistance to B. cinerea. Furthermore, we also observed pathogen induced anthocyanin accumulation at pathogen penetration sites in the white cultivars. Transcriptomics and metabolomics analyses revealed shift in metabolic pathways from flavonols towards flavone and anthocyanin biosynthesis during infections. A broader survey of taxonomically distant flowering species identified pathogen-induced red pigmentation is largely restricted to the members of the Asteraceae family. Notably, we observed divergence between wild and domesticated species, where the wild species retained the inducible pigmentation response and exhibited resistant to B. cinerea, whereas the cultivated species showed loss of this response, correlating with its increased susceptibility. Overall, our findings indicate that breeding for ornamental traits may have inadvertently selected against floral immunity.

plant biology↗

bioRxiv2026

The role of two GLYCOALKALOID METABOLISM genes in α-tomatine biosynthesis and basal defense in tomato

Steroidal glycoalkaloids and saponins are plant cholesterol-based steroid metabolites with antimicrobial activities and potential pharmacological value. The saponin uttroside B from black nightshade (Solanum nigrum) plays an important role in defense against herbivorous insect and exhibits anti-hepatocellular carcinoma activity. The tomato (S. lycopersicum) glycoalkaloid -tomatine has been studied because of its antinutritional effects, however, its role in protecting plants from fungal pathogens remains understudied. The biosynthetic pathway of -tomatine involves multiple clustered genes designated as glycoalkaloid metabolism (GAME) genes. In this study, we generated single knockout mutants of SlGAME4 and SlGAME2 by CRISPR/Cas9-based genome editing. The SlGAME4 mutants did not accumulate glycoalkaloids but instead redirected resources towards steroidal saponin (uttroside B) synthesis. SlGAME2 mutants contained unaltered -tomatine contents indicating that the SlGAME2 gene, previously reported to catalyze the transfer of xylose to {beta}1-tomatine, is not involved in -tomatine biosynthesis. Infection assays with four fungal tomato pathogens demonstrated that the SlGAME4 mutant plants were slightly more susceptible to Botrytis cinerea, but equally susceptible to the other three fungi. Up-regulation of -tomatine-responsive genes in B. cinerea was observed during infection on SlGAME4 mutant tomato, as well as on S. nigrum suggesting that uttroside B induces a fungal transcriptional response similar to -tomatine. Furthermore, we observed that tolerance mechanisms to plant saponins mediated by glycosyl hydrolases and a glycosyltransferase contribute to virulence of B. cinerea on SlGAME4 mutant plants and S. nigrum. This indicates that also uttroside B contributes to defense against fungal pathogens and can be detoxified by B. cinerea.

plant biology↗

bioRxiv2025

When flowers turn red: Pathogen induced flavonoid and anthocyanin biosynthesis in Chrysanthemum seticuspe confers resistanceto Botrytis cinerea

Botrytis cinerea is a major threat to ornamental crops, yet floral defence responses remain poorly understood. In Chrysanthemum seticuspe, we found that flower petals, unlike leaves, mount a localized resistance response resulting in red spots appearing at fungal penetration sites. We observed an intensification of the coloured response as infections progressed. To investigate the basis of this phenotype, we performed a time-course paired transcriptomic and metabolomic analysis on mock-inoculated vs B. cinerea-inoculated petals and leaves. Infection triggered strong transcriptional reprogramming in petals, with clear induction of phenylpropanoid and flavonoid/anthocyanin pathway genes and candidate regulators, consistent with the visible pigmentation. Metabolite profiles reflected this response, showing time-dependent accumulation of infection induced flavonoids such as quercetin, tilianin, and their derivatives, as well as cyanidin-based anthocyanins in infected petals. Integrating both omics datasets with MEANtools highlighted an anthocyanin-associated transcript-metabolite module, including a module putatively involved in the synthesis of polyyne-type phytoalexins. Antifungal assays demonstrated that selected flavonoids and cyanidin derivatives inhibit B. cinerea in a dose-dependent manner, supporting a direct antifungal role of these compounds. Altogether, our results show that C. seticuspe petals deploy a spatially confined, multi-layered chemical defence in which pathogen-induced flavonoids and anthocyanins operate as active components of resistance against a necrotrophic pathogen. We anticipate that future paired omics analyses in combination with spatial omics and bioactivity assays will yield insights into the role of specialised defence molecules in response to biotic and abiotic stresses. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/695701v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@e5dbeborg.highwire.dtl.DTLVardef@c94bd1org.highwire.dtl.DTLVardef@190c030org.highwire.dtl.DTLVardef@39a7b5_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗