Transcriptomic analysis reveals that reactive oxygen species and genes encoding lipid transfer protein are associated with tobacco hairy root growth and branch development

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.

Efficient CRISPR-mediated base editing in Agrobacterium spp

Agrobacterium spp. are important plant pathogens that are the causative agents of crown gall or hairy root disease. Their unique infection strategy depends on the delivery of part of their DNA to plant cells. Thanks to this capacity, these phytopathogens became a powerful and indispensable tool for plant genetic engineering and agricultural biotechnology. Although Agrobacterium spp. are standard tools for plant molecular biologists, current laboratory strains have remained unchanged for decades and functional gene analysis of Agrobacterium has been hampered by time-consuming mutation strategies. Here, we developed clustered regularly interspaced short palindromic repeats (CRISPR)-mediated base editing to enable the efficient introduction of targeted point mutations into the genomes of both Agrobacterium tumefaciens and Agrobacterium rhizogenes As an example, we generated EHA105 strains with loss-of-function mutations in recA, which were fully functional for maize (Zea mays) transformation and confirmed the importance of RolB and RolC for hairy root development by A. rhizogenes K599. Our method is highly effective in 9 of 10 colonies after transformation, with edits in at least 80% of the cells. The genomes of EHA105 and K599 were resequenced, and genome-wide off-target analysis was applied to investigate the edited strains after curing of the base editor plasmid. The off-targets present were characteristic of Cas9-independent off-targeting and point to TC motifs as activity hotspots of the cytidine deaminase used. We anticipate that CRISPR-mediated base editing is the start of "engineering the engineer," leading to improved Agrobacterium strains for more efficient plant transformation and gene editing.

Lipid Transfer Proteins (AaLTP3 and AaLTP4) Are Involved in Sesquiterpene Lactone Secretion from Glandular Trichomes in Artemisia annua

In Artemisia annua plants, glandular trichomes (GTs) are responsible for the biosynthesis and secretion of sesquiterpene lactones including artemisinin/arteannuin B. Nonspecific lipid transfer proteins (LTPs) in plants bind and carry lipid molecules across the cell membrane and are also known as secretary proteins. Interestingly, the transcripts of LTP genes are exceptionally abundant in the GTs of A. annua. In the present study, we isolated two trichome-specific LTP genes (AaLTP3 and AaLTP4) from a Korean ecotype of A. annua. AaLTP3 was expressed abundantly in shoots, whereas AaLTP4 was expressed in flowers. The GUS signal driven by the AaLTP3 or AaLTP4 promoter in transgenic A. annua plants revealed that the AaLTP3 promoter was active on hair-like non-GTs and that the AaLTP4 promoter was active on GTs. Analysis of enhanced cyan fluorescent protein (ECFP) fluorescence fused with the AaLTP3 or AaLTP4 protein in transgenic tobacco revealed that ECFP florescence was very bright on secreted lipids of long GTs. Moreover, the florescence was also bright on the head cells of short trichomes and their secreted granules. Immunoblotting analysis of GT exudates in petioles of A. annua revealed a strong positive signal against the AaLTP4 antibody. Overexpression of AaLTP3 or AaLTP4 in transgenic A. annua plants resulted in enhanced production of sesquiterpene lactones (arteannuin B, artemisinin, dihydroartemisinic acid and artemisinic acid) compared with those of wild type. The present study shows that LTP genes (AaLTP3 or AaLTP4) play important roles in the sequestration and secretion of lipids in GTs of A. annua, which is useful for the enhanced production of sesquiterpene lactones by genetic engineering.

Agrobacterium rhizogenes-mediated hairy roots transformation as a tool for exploring aluminum-responsive genes function

AIM

To develop a useful alternative approach to evaluate the gene function in hairy roots.

METHODS

Arabidopsis and tobacco (wild-type or mutant) were a host for Agrobacterium rhizogenes transformation.

RESULTS

The hairy roots formation efficiency ranged from 53 to 98% in tobacco and 53 to 66% in Arabidopsis. Hairy and intact roots showed similar gene expression pattern in response to salt and aluminum stress. Genomic polymerase chain reaction and fluorescent images showed high rate (>80%) of co-integration of T-DNAs and uniform cell transformation without use of any antibiotic selection. Whole processes of hairy roots were completed within 1 month after the infection of Agrobacterium.

CONCLUSION

Aluminum-responsive orthologous gene function could be evaluated by NtSTOP1-KD and Atstop1 as a host for hairy roots transformation.

Modulation of NADPH-oxidase gene expression in rolB-transformed calli of Arabidopsis thaliana and Rubia cordifolia

Expression of rol genes from Agrobacterium rhizogenes induces reprogramming of transformed plant cells and provokes pleiotropic effects on primary and secondary metabolism. We have previously established that the rolB and rolC genes impair reactive oxygen species (ROS) generation in transformed cells of Rubia cordifolia and Arabidopsis thaliana. In the present investigation, we tested whether this effect is associated with changes in the expression levels of NADPH oxidases, which are considered to be the primary source of ROS during plant-microbe interactions. We identified two full-length NADPH oxidase genes from R. cordifolia and examined their expression in non-transformed and rolB-transformed calli. In addition, we examined the expression of their homologous genes from A. thaliana in non-transformed and rolB-expressing cells. The expression of Rboh isoforms was 3- to 7-fold higher in both R. cordifolia and A. thaliana rolB-transformed cells compared with non-transformed cells. Our results for the first time show that Agrobacterium rolB gene regulates particular NADPH oxidase isoforms.