Genetic transformation of cauliflower (Brassica oleracea var. botrytis) by direct DNA uptake into mesophyll protoplasts

An Efficient and Universal Protoplast Isolation Protocol Suitable for Transient Gene Expression Analysis and Single-Cell RNA Sequencing

The recent advent of single-cell RNA sequencing (scRNA-seq) has enabled access to the developmental landscape of a complex organ by monitoring the differentiation trajectory of every specialized cell type at the single-cell level. A main challenge in this endeavor is dissociating plant cells from the rigid cell walls and some species are recalcitrant to such cellular isolation. Here, we describe the establishment of a simple and efficient protocol for protoplast preparation in Chirita pumila, which includes two consecutive digestion processes with different enzymatic buffers. Using this protocol, we generated viable cell suspensions suitable for an array of expression analyses, including scRNA-seq. The universal application of this protocol was further tested by successfully isolating high-quality protoplasts from multiple organs (petals, fruits, tuberous roots, and gynophores) from representative species on the key branches of the angiosperm lineage. This work provides a robust method in plant science, overcoming barriers to isolating protoplasts in diverse plant species and opens a new avenue to study cell type specification, tissue function, and organ diversification in plants.

High efficiency transformation of Brassica oleracea var. botrytis plants by Rhizobium rhizogenes

Brassica oleracea var. botrytis, a very popular crop grown for its edible inflorescence, is bred only as a mutated annual cultivar and does not naturally occur in environment. Since cauliflower is still described as the most troublesome of all the B. oleracea vegetables regarding transformation processes, it is fully justified to focus on the improvement of tools for its genetic modifications. Here, we present a successful protocol for genetic transformation of cauliflower employing the process of agroinfection. The primary analysis of in vitro response of five cultivars allowed us to have chosen Pionier as the most promising cultivar; in consequence the Pionier was transformed via Rhizobium-mediated techniques in order to evaluate both, R. radiobacter (EHA 105, LBA 4404) and R. rhizogenes (ATCC 18534, A4) species. However, the latter system turned out to be more effective and, the A4 strain, in particular (72% transformation efficiency, 55% confirmed by GUS assay). That shows a promising technical advance especially when compared to the results of previous literature reports (e.g. 8.7% reported efficiency using R. rhizogenes). The transgenic cauliflower was obtained from hairy roots via organogenic callus induction. The potential transformants were analysed at the genomic and proteomic levels and their transgenic character was fully confirmed.

A novel in vitro transformation of Lepidium draba L. using rapid direct shoot regeneration

The present research is carried out to study Lepidium draba gene transformation for the first time, using direct shoot explants. As a prerequisite for gene transformation, the regeneration conditions in L. draba were optimized. We achieved an efficient and reproducible protocol for successful direct shoot regeneration without intervening callus formation. The results indicate that L. draba is the insistent species of Brassicaceae in direct shoot regeneration. Various explants of L. draba were genetically transformed with different strains of Agrobacterium tumefaciens, viz., LBA4404, GV3850, GV3101, and EHA105, using the vector pBI121. Expression of GUS reporter protein was assayed by histochemical staining. In addition, using the PCR method with specific primers proved the integration of GUS gene into the plants. The highest transformation efficiency was achieved with Agrobacterium strain GV3850. Moreover, we found that infected hypocotyl and root explants of L. draba interestingly yielded higher transformation efficiency, so that in hypocotyls on average exceeded 70% of the explants. This study showed that L. draba, in addition to the numerous desirable traits, has a high potential for gene transfer.

Biotechnological advancement in genetic improvement of broccoli (Brassica oleracea L. var. italica), an important vegetable crop

With the advent of molecular biotechnology, plant genetic engineering techniques have opened an avenue for the genetic improvement of important vegetable crops. Vegetable crop productivity and quality are seriously affected by various biotic and abiotic stresses which destabilize rural economies in many countries. Moreover, absence of proper post-harvest storage and processing facilities leads to qualitative and quantitative losses. In the past four decades, conventional breeding has significantly contributed to the improvement of vegetable yields, quality, post-harvest life, and resistance to biotic and abiotic stresses. However, there are many constraints in conventional breeding, which can only be overcome by advancements made in modern biology. Broccoli (Brassica oleracea L. var. italica) is an important vegetable crop, of the family Brassicaceae; however, various biotic and abiotic stresses cause enormous crop yield losses during the commercial cultivation of broccoli. Thus, genetic engineering can be used as a tool to add specific characteristics to existing cultivars. However, a pre-requisite for transferring genes into plants is the availability of efficient regeneration and transformation techniques. Recent advances in plant genetic engineering provide an opportunity to improve broccoli in many aspects. The goal of this review is to summarize genetic transformation studies on broccoli to draw the attention of researchers and scientists for its further genetic advancement.

An alginate-layer technique for culture of Brassica oleracea L. protoplasts

Ten accessions belonging to the Brassica oleracea subspecies alba and rubra, and to B. oleracea var. sabauda were used in this study. Protoplasts were isolated from leaves and hypocotyls of in vitro grown plants. The influence of selected factors on the yield, viability, and mitotic activity of protoplasts immobilized in calcium alginate layers was investigated. The efficiency of protoplast isolation from hypocotyls was lower (0.7 ± 0.1 × 10(6) ml(-1)) than for protoplasts isolated from leaf mesophyll tissue (2 ± 0.1 × 10(6) ml(-1)). High (70-90%) viabilities of immobilized protoplasts were recorded, independent of the explant sources. The highest proportion of protoplasts undergoing divisions was noted for cv. Reball F1, both from mesophyll (29.8 ± 2.2%) and hypocotyl (17.5 ± 0.3%) tissues. Developed colonies of callus tissue were subjected to regeneration and as a result plants from six accessions were obtained.

Quantitative trait loci affecting plant regeneration from protoplasts of Brassica oleracea

Quantitative trait loci (QTLs) controlling the plant-regeneration ability of Brassica oleracea protoplasts were mapped in a population of 128 F(2) plants derived from a cross between the high-responding, rapid-cycling line and a low-responding, broccoli breeding line of B. oleracea. A modified bulked segregant analysis with AFLP markers identified two QTLs for plant regeneration. In a multiple regression analysis, the two QTLs explained 83% of the total genetic variation for regeneration recorded 15 weeks after initial transfer of microcalli to regeneration medium. Both QTLs showed additive effects, and the alleles contributing to the high regeneration frequencies were derived from the high-responding, rapid-cycling line. Using microsatellites with known location, the two QTLs were mapped to linkage groups O2 and O9 on the map published by Sebastian et al. [(2000) Theor Appl Genet 100:75-81] or to chromosomes C8 and C7 on the map published by Saal et al. [(2001) Theor Appl Genet 102:695-699]. QTLs for the early flowering trait of the rapid-cycling parent have previously been mapped to the same two linkage groups. Association between flowering time and regeneration ability was, however, not found in the present material, indicating that plant-regeneration ability can be transferred between cultivars independently of the early flowering trait. The detection of two major QTLs for plant regeneration in B. oleracea may provide the initial step towards the identification of markers suitable for marker-assisted selection of regeneration ability.