Biology subjects

Kilambi, H. V.

Publications and source records attributed to Kilambi, H. V..

4 recordsLinked to original sources

bioRxiv2025

Loss-of-Function RUP-Variants Influence Ubiquitin-Proteasome System and Enhance Carotenoid and Folate Levels in Tomato

REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) negatively regulates UV- B signalling, yet its broader physiological roles in crop plants remain largely unexplored. We compared two tomato accessions bearing truncated RUP proteins--rup-1 and rup-2 (rup- variants)--with the cultivar Arka Vikas (AV), which harbours the native RUP protein. Seedlings of rup-variants exhibited enhanced tolerance to supplemental UV-B light. Red ripe (RR) fruits of rup-variants showed significantly elevated carotenoid and folate levels compared to AV. Introgression of rup-variants into AV confirmed that the increased carotenoid accumulation is genetically linked to RUP truncation. Metabolomic profiling of rup-variants revealed a substantial shift in primary metabolic homeostasis, particularly at the breaker stage, marked by a pronounced reduction in sugars and amino acids. Proteomic analyses of rup- variants across ripening stages identified that a significant proportion of differentially expressed proteins belonged to chaperones and ubiquitin-proteasome system (UPS). Upregulation of four key enzymes in the carotenoid biosynthesis pathway likely contributed to increased lycopene content in rup-variants. Elevated folate levels in rup-variants were associated with the upregulation of folate biosynthesis and C1 metabolism enzymes. Despite widespread metabolic reprogramming in rup-variants, hormonal regulatory pathways remained largely unaltered. Our results suggest that RUP modulates metabolic pathways during fruit ripening, and its loss triggers metabolic reprogramming associated with elevated folate/carotenoid levels.

plant biology↗

bioRxiv2023

A tomato ethylene-insensitive mutant displays altered growth and higher β-carotene levels in fruit

The mutants insensitive to ethylene are helpful in deciphering the role of ethylene in plant development. We isolated an ethylene-insensitive tomato (Solanum lycopersicum) mutant by screening for acetylene-resistant (atr-1) seedlings. The atr-1 mutant displayed resistance to kinetin, suggesting attenuation of the ethylene sensing response. atr-1 also exhibited resistance to ABA- and glucose-mediated inhibition of seed germination. Unlike the Never- ripe (Nr) mutant, atr-1 seedlings were resistant to glucose, indicating ethylene sensing in atr-1 is located in a component distinct from Nr. Metabolically, atr-1 seedlings had lower levels of amino acids but higher levels of several phytohormones, including ABA. atr-1 plants grew faster and produced more flowers, leading to a higher fruit set. However, the atr- 1 fruits took a longer duration to reach the red-ripe (RR) stage. The ripened atr-1 fruits had higher {beta}-carotene levels, retained high {beta}-carotene and lycopene levels post-RR stage. The metabolome profiles of post-RR stage atr-1 fruits revealed increased levels of sugars. The atr-1 had a P279L mutation in the GAF domain of the ETR4, a key ethylene receptor regulating tomato ripening. Our study highlights that novel alleles in ethylene receptors may aid in enhancing the nutritional quality of tomato.

plant biology↗

bioRxiv2022

Reduced γ-glutamyl hydrolase activity likely contributes to high folate levels in Periyakulam-1 tomato

Tomato cultivars show wide variation in nutraceutical folate in ripe fruits, yet the loci regulating folate levels in fruits remain unexplored. To decipher regulatory points, we compared two contrasting tomato cultivars: Periyakulam-1 (PKM-1) with high folate and Arka Vikas (AV) with low folate. The progression of ripening in PKM-1 was nearly similar to AV but had substantially lower ethylene emission. In parallel, the levels of phytohormones salicylic acid, ABA, and jasmonic acid were substantially lower than AV. The fruits of PKM-1 were also metabolically distinct from AV, with upregulation of several amino acids. Consistent with higher {degrees}Brix levels, the red ripe fruits also showed upregulation of sugars and sugar-derived metabolites. In parallel with higher folate, PKM-1 fruits also had higher carotenoid levels, especially lycopene and {beta}-carotene. Transcript levels of genes encoding folate biosynthesis did not show a perceptible difference in relative expression. The proteome analysis showed upregulation of carotenoid sequestration and folate metabolism-related proteins in PKM-1. The deglutamylation pathway mediated by {gamma}-glutamyl hydrolase (GGH) was substantially reduced in PKM-1 at the red-ripe stage. The red-ripe fruits had reduced transcript levels of GGHs and lower GGH activity than AV. Conversely, the percent polyglutamylation of folate was much higher in PKM-1. Our analysis indicates the regulation of GGH activity as a potential target to elevate folate levels in tomato fruits.

plant biology↗

bioRxiv2020

The new kid on the block: A dominant-negative mutation of phototropin1 enhances carotenoid content in tomato fruits

Phototropins, the UVA-blue light photoreceptors, endow plants to detect the direction of light and optimize photosynthesis by regulating chloroplasts positioning and stomatal gas exchange. Little is known about their functions in other developmental responses. A tomato Non-phototropic seedling1 (Nps1) mutant, bearing an Arg495His substitution in the vicinity of LOV2 domain in phototropin1, dominant-negatively blocks phot1 and phot2 responses. The fruits of Nps1 mutant were enriched in carotenoids, particularly lycopene, than its parent, Ailsa Craig. Contrarily, CRISPR/CAS9-edited loss of function phototropin1 mutants displayed subdued carotenoids than the parent. The enrichment of carotenoids in Nps1 fruits is genetically linked with the mutation and exerted in a dominant-negative fashion. Nps1 also altered volatile profiles with high levels of lycopene-derived 6-methyl 5-hepten2-one. The transcript levels of several MEP and carotenogenesis pathways genes were upregulated in Nps1. Nps1 fruits showed altered hormonal profiles with subdued ethylene emission and reduced respiration. Proteome profiles showed a causal link between higher carotenogenesis and increased levels of protein protection machinery, which may stabilize proteins contributing to MEP and carotenogenesis pathways. Given the enhancement of carotenoid content by Nps1 in a dominant-negative fashion, it offers a potential tool for high lycopene-bearing hybrid tomatoes. One-sentence summaryA dominant-negative phototropin1 mutation enhances carotenoid levels, alters metabolite homeostasis, and protein quality control machinery in tomato fruits.

plant biology↗