Characterization of transcription of genes involved in hairy root induction on pRi1724 core-T-DNA in two Ajuga reptans hairy root lines

Hairy root culture as a valuable tool for allelopathic studies in apple

Allelopathic plants exploit their chemical 'weapons' to prevail over the competition, suppress neighboring plants and consequently use the available resources more efficiently. However, the investigation of plant allelopathic interactions in rhizosphere is difficult to perform because of its high complexity due to interactions of biotic and abiotic factors. Thus, autonomous, aseptic root cultures of apple (Malus × domestica Borkh.) could facilitate allelopathic studies. We report on the successful genetic transformation of apple cultivars Melrose, Golden Delicious, Čadel and Gloster using Agrobacterium rhizogenes (Riker et al. 1930) Conn 1942 strain 15834 and for the first time the establishment of apple autonomous and permanent in vitro hairy root cultures that could be used as a new tool for apple allelopathic assays. Molecular characterization of transgenic hairy root lines was conducted to elucidate the possible relationship between expression of T-DNA genes and root growth characteristics that include branching. Similar content of phenolic acids (chlorogenic, caffeic, syringic, p-coumaric and ferulic), glycosilated flavonoids (rutin, quercitrin, isoquercitrin, kaempferol-3-glucoside) and flavonoid aglycones (quercetin and naringenin), and dihydrochalcone phloridzin, was detected in untransformed and transgenic apple root tissue by ultra high-performance liquid chromatography with mass spectrometry (UHPLC/(+/-)HESI-MS/MS) analyses, confirming that genetic transformation did not disturb secondary metabolite production in apple. Chlorogenic and caffeic acids and dihydrochalcones phloridzin and phloretin were detected as putative allelochemicals exuded into the growth medium in which transgenic roots were maintained for 4 weeks. Apple hairy root exudates significantly affected shoot and root development and growth of test plant Arabidopsis thaliana (L.) Heynh. seedlings after 5 or 10 days of treatment. Additionally, core cell-cycle genes CDKA1;1, CDKB2;1, CYCA3;1 and CYCB2;4 were down regulated in Arabidopsis shoots suggesting, in part, their role in inhibition of shoot growth. The present work highlighted an autonomous and permanent in vitro hairy root culture system as a valuable tool for studying allelopathic potential of apple, offering new perspective for allelopathy background elucidation in this important fruit species.

Overexpression of Cinnamate 4-Hydroxylase and 4-Coumaroyl CoA Ligase Prompted Flavone Accumulation inScutellaria baicalensisHairy Roots

Scutellaria baicalensis Georgi, a species of the Lamiaceae family, is considered as one of the 50 fundamental herbs used in traditional Chinese medicine. In order to enhance flavone (baicalein, baicalin, and wogonin) content in S. baicalensis roots, we overexpressed a single gene of cinnamate 4-hydroxylase (C4H) and 4-coumaroyl coenzyme A ligase (4CL) using an Agrobacterium rhizogenes-mediated system. SbC4H- and Sb4CL-overexpressed hairy root lines enhanced the transcript levels of SbC4H and Sb4CL compared with those in the control and also increased flavones contents by approximately 3- and 2.5-fold, respectively. We successfully engineered the flavone biosynthesis pathway for the production of beneficial flavones in S. baicalensis hairy roots. The importance of upstream gene C4H and 4CL in flavone biosynthesis and the efficiency of metabolic engineering in promoting flavone biosynthesis in S. baicalensis hairy roots have been indicated in this study.

Hairy root cultures for secondary metabolites production

Hairy roots (HRs) are differentiated cultures of transformed roots generated by the infection of wounded higher plants with Agrobacterium rhizogenes. This pathogen causes the HR disease leading to the neoplastic growth of roots that are characterized by high growth rate in hormone free media and genetic stability. HRs produce the same phytochemicals pattern of the corresponding wild type organ. High stability and productivity features allow the exploitation of HRs as valuable biotechnological tool for the production of plant secondary metabolites. In addition, several elicitation methods can be used to further enhance their accumulation in both small and large scale production. However, in the latter case, cultivation in bioreactors should be still optimized. HRs can be also utilised as biological farm for the production of recombinant proteins, hence holding additional potential for industrial use. HR technology has been strongly improved by increased knowledge of molecular mechanisms underlying their development. The present review summarizes updated aspects of the hairy root induction, genetics and metabolite production.

Nuclear localization and interaction of RolB with plant 14-3-3 proteins correlates with induction of adventitious roots by the oncogene rolB

The rooting-locus gene B (rolB) on the T-DNA of the root-inducing (Ri) plasmid in Agrobacterium rhizogenes is responsible for the induction of transformed adventitious roots, although the root induction mechanism is unknown. We report here that the RolB protein of pRi1724 (1724RolB) is associated with Nicotianatabacum14-3-3-like protein omegaII (Nt14-3-3 omegaII) in tobacco bright yellow (BY)-2 cells. Nt14-3-3 omegaII directly interacts with 1724RolB protein. Green fluorescent protein (GFP)-fused 1724RolB is localized to the nucleus. GFP-fused mutant 1724RolB proteins having a deletion or amino acid substitution are unable to interact with Nt14-3-3 omegaII and also show impaired nuclear localization. Moreover, these 1724RolB mutants show decreased capacity for adventitious root induction. These results suggest that adventitious root induction by 1724RolB protein correlates with its interaction with Nt14-3-3 omegaII and the nuclear localization of 1724RolB protein.

Gene expression activity and pathway selection for sucrose metabolism in developing storage root of sweet potato

Development of sweet potato (Ipomoea batatas) storage root coincides with starch accumulation made using cleaved products of imported photoassimilate sucrose. The genes and pathways are predominantly active for sucrose metabolism in developing storage root were unknown. In this study, we used both an expressed sequence tag (EST) approach and a reverse transcription-polymerase chain reaction (RT-PCR) approach to answer this question. Sucrose synthase (SuSy) was found to be significantly more frequent in storage root ESTs than in fibrous root ESTs. SuSy was the most abundant carbohydrate-metabolism gene in the storage-root ESTs. RT-PCR results confirmed this by showing that invertase was active in fibrous roots but rapidly decreased to an undetectable level during storage root development while SuSy became predominant. Invertase expression was also detectable in young immature storage root and shoot tips, suggesting an involvement in cell formation. SuSy expression pattern showed considerable similarity to that of ADP-glucose pyrophosphorylase, an essential enzyme for starch synthesis. The results indicated that (i). SuSy was the most actively expressed enzyme in sucrose metabolism in developing storage root and was correlated with sink strength, and (ii). whereas invertase was active at cell formation stages, SuSy pathway was predominant for sucrose cleavage related to starch-accumulation.

Tobacco plants were transformed by Agrobacterium rhizogenes infection during their evolution

We discovered that the origin of cT-DNA in the genome of wild-type Nicotiana glauca is the T-DNA of the mikimopine-type Ri plasmid (pRi) harbored in Agrobacterium rhizogenes. The cT-DNA was inserted into the genomic DNA of N. glauca from the position corresponding to the right border of mikimopine-type pRi. The cT-DNA contained two mikimopine synthase gene (mis) homologs, NgmisL and NgmisR, both of which were transcribed at low level in all N. glauca organs. NgMisR protein expressed in Escherichia coli has preserved Mis activity, which converts l-histidine and alpha-ketoglutaric acid to mikimopine. The mis homolog was also found in the genome of three other Nicotiana species: N. tomentosa, N. tomentosiformis, and N. tabacum; however, the site of insertion differed from that in N. glauca, suggesting that A. rhizogenes harboring mikimopine-type pRi independently infected the ancestors of some Nicotiana plants. This is the first clear evidence of a host-parasite relationship during the early evolution of Nicotiana plants. We propose that a new phylogenetic approach using opine type cT-DNA is applicable for presuming divergence in the genus Nicotiana.

Mikimopine synthase (mis) gene on pRi1724

By determination of the nucleotide sequence adjacent to the right border of T-DNA of the mikimopine-type Ri plasmid (pRi1724) in Agrobacterium rhizogenes, a new open reading frame (ORF) encoding 318 amino acids was found. A transcript of 1.35 kb derived from this ORF was observed in hairy roots of Ajuga reptans by northern blotting analysis. Including its own promoter and terminator, this ORF was isolated from the pRi1724 T-DNA and introduced into tobacco plants by the Agrobacterium-binary vector system. Since mikimopine, an opine and a stereoisomer of cucumopine, was accumulated in all organs of the transgenic tobacco plants, the new ORF was deduced to be the mikimopine synthase gene. For comparison, the nucleotide sequence of cucumopine synthase encoded on pRi2659 was also determined. No homology was found between mikimopine synthase and cucumopine synthase at the nucleotide, but partial homology was found at the amino acid level. Mikimopine synthase and cucumopine synthase produced by a protein expression system using E. coli catalyzed the synthesis of mikimopine and cucumopine from L-histidine and alpha-ketoglutaric acid, requiring NADH as a cofactor. These synthesized opines were identified by paper electrophoresis, TLC and HPLC analyses. The synthesized mikimopine or cucumopine could be degraded by A. rhizogenes strains harboring Ri plasmids encoding the respective catabolic enzyme.