Agrobacterium rhizogenes rolB oncogene: An intriguing player for many roles

Enhanced production of withaferin A from the hairy root culture of Withania somnifera via synergistic effect of Methyl jasmonate and β-cyclodextrin

Due to low amounts of withanolides produced in some plants and high demand for various applications, their biotechnological production is widely researched. The effects of two explant types (i.e., leaf and stem from the in vitro seedlings of three genotypes of Withania somnifera) and four Rhizobium strains (i.e., LBA 9402, A4, ATCC 15834, and C58C1) to improve hairy root formation efficiency was studied. Furthermore, the combined effects of β-cyclodextrin (β-CD) and methyl jasmonate (MeJA) on withaferin A production after 48 h exposure time was examined. Four hairy roots having the maximum percentage of induced roots and mean number of induced roots to analyze their growth kinetics and identified G3/ATCC/LEAF culture having the maximum specific growth rate (μ = 0.036 day-1) and growth index (GI = 9.18), and the shortest doubling time (Td = 18.82 day) were selected. After 48 h exposure of G3/ATCC/LEAF culture to different elicitation conditions, maximum amounts of withaferin A were produced in samples co-treated with 0.5 mM β-CD + 100 μM MeJA (9.57 mg/g DW) and 5.0 mM β-CD + 100 μM MeJA (17.45 mg/g DW). These outcomes represented a 6.8-fold and 12.5-fold increase, respectively, compared to the control. Similarly, combined β-CD/MeJA elicitation increased gene expression levels of HMGR, SQS, SMT-1, and SDS/CYP710A involved in withanolides biosynthetic pathway, of which just SMT-1 had significant correlation with withaferin A production. These results demonstrated the superiority of G1-leaf explant and ATCC 15834 for hairy root induction, and revealed synergistic effect of MeJA and β-CD on withaferin A production.

Salicylic acid and jasmonic acid biosynthetic pathways are simultaneously activated in transgenic Arabidopsis expressing the rolB/C gene from Ipomoea batatas

The Agrobacterium rhizogenes root oncogenic locus (rol) genes interfere with hormone balance by altering their synthesis and/or recognition, giving rise to varied impacts on the physiological characteristics of plants and cell cultures. The homolog of the rolB and rolC genes from Ipomoea batatas, named Ib-rolB/C, similarly induces morphological and physiological alterations in transgenic Arabidopsis thaliana; however, its role in plant hormonal homeostasis has not been previously defined. In this study, we found that external application of salicylic acid (SA) and methyl jasmonate (MeJA) significantly upregulated Ib-rolB/C in detached I. batatas leaves. Furthermore, heterologous expression of Ib-rolB/C in A. thaliana markedly enhanced the accumulation of SA and MeJA, and to a lesser extent, elevated abscisic acid (ABA) levels, through the modulation of genes specific to hormone biosynthesis. Even though the RolB/RolC homolog protein has a notable structural resemblance to the RolB protein from A. rhizogenes, it exhibits a distinct localization pattern, predominantly residing in the cytoplasm and certain discrete subcellular structures, instead of the nucleus. Consequently, the functions of RolB/RolC in both naturally and artificially transgenic plants are linked to changes in the hormonal state of the cells, though the underlying signaling pathways remain to be elucidated.

Accumulation of phenolic compounds and expression of phenylpropanoid biosynthesis-related genes in leaves of basil transformed with A. rhizogenes strains

Biotic factors affect the content of secondary metabolites by interfering with molecular and biochemical pathways. In the current study, A. rhizogenes strains were inoculated into basil (Ocimum basilicum) to examine the effect of plant-microbe interaction on the accumulation of monomeric phenolic metabolites and the transcript levels of selected genes involved in the biochemical synthesis of secondary compounds. Initially, the integration of the rolB gene was validated by performing PCR analysis on genomic DNA samples from the basil plant inoculated with A. rhizogenes strains. We have detected that the accumulation of mRNA transcripts linked to the biosynthesis pathway of phenolic compounds has higher transcript expression levels in the leaves of transformed basil in proportion to uninoculated plants. Basil plants inoculated with A. rhizogenes 39207 strain had higher transcript levels of CAD, C4H, TAT, FLS, EGS, HPPR, PAL, and RAS genes than other experimental groups. We have identified eleven phenolic components, and the level of rosmarinic acid, eugenol, chicoric acid, and rutin increased in the inoculated basil leaves. However, the inoculation of A. rhizogenes did not cause a change in the compounds of chlorogenic acid, methyl chavicol, cinnamic acid, quercetin, vanillic acid, and caffeic acid. In conclusion, the increase in basic secondary metabolites could be achieved by the A. rhizogenes-mediated transformation of basil plants, and especially ATCC 43057 strain may be one of the A. rhizogenes strains.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01320-w.

Proteomic Analysis of Proteins Related to Defense Responses in Arabidopsis Plants Transformed with the rolB Oncogene

During Agrobacterium rhizogenes-plant interaction, the rolB gene is transferred into the plant genome and is stably inherited in the plant's offspring. Among the numerous effects of rolB on plant metabolism, including the activation of secondary metabolism, its effect on plant defense systems has not been sufficiently studied. In this work, we performed a proteomic analysis of rolB-expressing Arabidopsis thaliana plants with particular focus on defense proteins. We found a total of 77 overexpressed proteins and 64 underexpressed proteins in rolB-transformed plants using two-dimensional gel electrophoresis and MALDI mass spectrometry. In the rolB-transformed plants, we found a reduced amount of scaffold proteins RACK1A, RACK1B, and RACK1C, which are known as receptors for activated C-kinase 1. The proteomic analysis showed that rolB could suppress the plant immune system by suppressing the RNA-binding proteins GRP7, CP29B, and CP31B, which action are similar to the action of type-III bacterial effectors. At the same time, rolB plants induce the massive biosynthesis of protective proteins VSP1 and VSP2, as well as pathogenesis-related protein PR-4, which are markers of the activated jasmonate pathway. The increased contents of glutathione-S-transferases F6, F2, F10, U19, and DHAR1 and the osmotin-like defense protein OSM34 were found. The defense-associated protein PCaP1, which is required for oligogalacturonide-induced priming and immunity, was upregulated. Moreover, rolB-transformed plants showed the activation of all components of the PYK10 defense complex that is involved in the metabolism of glucosinolates. We hypothesized that various defense systems activated by rolB protect the host plant from competing phytopathogens and created an effective ecological niche for A. rhizogenes. A RolB → RACK1A signaling module was proposed that might exert most of the rolB-mediated effects on plant physiology. Our proteomics data are available via ProteomeXchange with identifier PXD037959.

Overexpression of the A4-rolB gene from the pRiA4 of Rhizobium rhizogenes modulates hormones homeostasis and leads to an increase of flavonoid accumulation and drought tolerance in Arabidopsis thaliana transgenic plants

Increased flavonol accumulation and enhanced drought tolerance in A4-rolB-overexpressing plants can be explained by the cooperative action of the SA and ROS signalling pathways. Clarification of function of the A4-rolB plast gene from pRiA4 of Rhizobium rhizogenes will allow a better understanding of the biological principles of the natural transformation process and its use as a tool for plant bioengineering. In the present study, we investigated whether the overexpression of A4-rolB gene could regulate two important processes, flavonoid biosynthesis and drought tolerance. In addition, we investigated some aspects of the possible machinery of the A4-rolB-induced changes in plant physiology, such as crosstalk of the major signalling systems. Based on the data obtained in this work, it can be presumed that constitutive overexpression of A4-rolB leads to the activation of the salicylic acid signalling system. An increase in flavonol accumulation and enhanced drought tolerance can be explained by the cooperative action of SA and ROS pathways.

Antibacterial, Antihemolytic, Cytotoxic, Anticancer, and Antileishmanial Effects of Ajuga bracteosa Transgenic Plants

Herbal and traditional medicines can play a pivotal role in combating cancer and neglected tropical diseases. Ajuga bracteosa, family Lamiaceae, is an important medicinal plant. The genetic transformation of A. bracteosa with rol genes of Agrobacterium rhizogenes further enhances its metabolic content. This study aimed at undertaking the molecular, phytochemical, and in vitro biological analysis of A. bracteosa extracts. We transformed the A. bracteosa plant with rol genes and raised the regenerants from the hairy roots. Transgenic integration and expression of rolB were confirmed by conventional polymerase chain reaction (PCR) and qPCR analysis. The methanol: chloroform crude extracts of wild-type plants and transgenic regenerants were screened for in vitro antibacterial, antihemolytic, cytotoxic, anticancer, and leishmanial activity. Among all plants, transgenic line 3 (ABRL3) showed the highest expression of the rolB gene. Fourier transform infra-red (FTIR) analysis confirmed the enhanced number of functional groups of active compounds in all transgenic lines. Moreover, ABRL3 exhibited the highest antibacterial activity, minimum hemolytic activity (CC₅₀ = 7293.05 ± 7 μg/mL) and maximum antileishmanial activity (IC₅₀ of 56.16 ± 2 μg/mL). ABRL1 demonstrated the most prominent brine shrimp cytotoxicity (LD₅₀39.6 ± 4 μg/mL). ABRL3 was most effective against various human cancer cell lines with an IC₅₀ of 57.1 ± 2.2 μg/mL, 46.2 ± 1.1 μg/mL, 72.4 ± 1.3 μg/mL, 73.3 ± 2.1 μg/mL, 98.7 ± 1.6 μg/mL, and 97.1 ± 2.5 μg/mL against HepG2, LM3, A549, HT29, MCF-7, and MDA-MB-231, respectively. Overall, these transgenic extracts may offer a cheaper therapeutic source than the more expensive synthetic drugs.