Regeneration and identification of interspecific asymmetric somatic hybrids obtained by donor-recipient fusion in cotton

A highly efficient protocol for isolation of protoplast from China, Assam and Cambod types of tea plants [Camellia sinensis (L.) O. Kuntze]

BACKGROUND

Tea is the most popular beverage worldwide second only to water. Its demand is tremendously rising due to increased awareness of its medicinal importance. The quality and uses of tea depend on the tea-types which are mainly three types including China, Assam and Cambod type having distinct compositions of secondary metabolites. Huge variation in secondary metabolites in different tea-types and cultivars limited the successful application of various approaches used for its trait improvement. The efficiency of a protocol for isolation of protoplast is specific to the types and cultivars of tea plants. The existing tea protoplast-isolation protocols [which were optimized for tea-types (China and Assam type) and Chinese cultivars grown in China] were found ineffective on types/cultivars grown in India due to type/cultivar variability. Therefore, optimization of protoplast-isolation protocol is essential for tea-types/cultivars grown in India, as it is the second largest producer of tea and the largest producer of black tea. Here, efforts were made to develop an efficient protoplast-isolation protocol from all major types of tea (China, Assam and Cambod types) grown in India and also from three types of tender leaves obtained from field-grown, hydroponically-grown and tissue culture-grown tea plants.

RESULTS

Developed protoplast-isolation protocol was effective for different types of leaf tissue obtained from the tender leaves of field-grown, hydroponically-grown and tissue culture-grown tea plants. Moreover, optimized protocol effectively worked on all three types of tea including China, Assam and Cambod types cultivated in India. The digestion of leaves with 3% cellulase R-10, 0.6% macerozyme, 1% hemicellulase and 4% polyvinylpyrrolidone for 12 h at 28ºC yielded approximately 3.8-4.6 × 107 protoplasts per gram fresh tissue and 80-95% viability in selected tea cultivars, and tissue culture plant material was found most appropriate for protoplast isolation.

CONCLUSIONS

In conclusion, we reported an efficient protocol for isolation of protoplasts from tender tea leaves of all major tea-types (China, Assam and Cambod) grown in India. Moreover, the protocol is also effective for tender-leaf tissue of field-grown, hydroponically-grown and tissue culture-grown tea plants. The findings are expected to contribute to the genetic improvement of tea traits widely.

Isolation, purification and PEG-mediated transient expression of mesophyll protoplasts in Camellia oleifera

BACKGROUND

Camellia oleifera (C. oleifera) is a woody edible oil crop of great economic importance. Because of the lack of modern biotechnology research, C. oleifera faces huge challenges in both breeding and basic research. The protoplast and transient transformation system plays an important role in biological breeding, plant regeneration and somatic cell fusion. The objective of this present study was to develop a highly efficient protocol for isolating and purifying mesophyll protoplasts and transient transformation of C. oleifera. Several critical factors for mesophyll protoplast isolation from C. oleifera, including starting material (leaf age), pretreatment, enzymatic treatment (type of enzyme, concentration and digestion time), osmotic pressure and purification were optimized. Then the factors affecting the transient transformation rate of mesophyll protoplasts such as PEG molecular weights, PEG4000 concentration, plasmid concentration and incubation time were explored.

RESULTS

The in vitro grown seedlings of C. oleifera 'Huashuo' were treated in the dark for 24 h, then the 1st to 2nd true leaves were picked and vacuumed at - 0.07 MPa for 20 min. The maximum yield (3.5 × 10⁷/g·FW) and viability (90.9%) of protoplast were reached when the 1st to 2nd true leaves were digested in the enzymatic solution containing1.5% (w/v) Cellulase R-10, 0.5% (w/v) Macerozyme R-10 and 0.25% (w/v) Snailase and 0.4 M mannitol for 10 h. Moreover, the protoplast isolation method was also applicable to the other two cultivars, the protoplast yield for 'TXP14' and 'DP47' was 1.1 × 10⁷/g·FW and 2.6 × 10⁷/g·FW, the protoplast viability for 'TXP14' and 'DP47' was 90.0% and 88.2%. The purification effect was the best when using W buffer as a cleaning agent by centrifugal precipitation. The maximum transfection efficiency (70.6%) was obtained with the incubation of the protoplasts with 15 µg plasmid and 40% PEG4000 for 20 min.

CONCLUSION

In summary, a simple and efficient system for isolation and transient transformation of C. oleifera mesophyll protoplast is proposed, which is of great significance in various aspects of C. oleifera research, including the study of somatic cell fusion, genome editing, protein function, signal transduction, transcriptional regulation and multi-omics analyses.

An integrated proteomic and metabolomic study to evaluate the effect of nucleus-cytoplasm interaction in a diploid citrus cybrid between sweet orange and lemon

Our results provide a comprehensive overview how the alloplasmic condition might lead to a significant improvement in citrus plant breeding, developing varieties more adaptable to a wide range of conditions. Citrus cybrids resulting from somatic hybridization hold great potential in plant improvement. They represent effective products resulting from the transfer of organelle-encoded traits into cultivated varieties. In these cases, the plant coordinated array of physiological, biochemical, and molecular functions remains the result of integration among different signals, which derive from the compartmentalized genomes of nucleus, plastids and mitochondria. To dissect the effects of genome rearrangement into cybrids, a multidisciplinary study was conducted on a diploid cybrid (C2N), resulting from a breeding program aimed to improve interesting agronomical traits for lemon, the parental cultivars 'Valencia' sweet orange (V) and 'femminello' lemon (F), and the corresponding somatic allotetraploid hybrid (V + F). In particular, a differential proteomic analysis, based on 2D-DIGE and MS procedures, was carried out on leaf proteomes of C2N, V, F and V + F, using the C2N proteome as pivotal condition. This investigation revealed differentially represented protein patterns that can be associated with genome rearrangement and cell compartment interplay. Interestingly, most of the up-regulated proteins in the cybrid are involved in crucial biological processes such as photosynthesis, energy production and stress tolerance response. The cybrid differential proteome pattern was concomitant with a general increase of leaf gas exchange and content of volatile organic compounds, highlighting a stimulation of specific pathways that can be related to observed plant performances. Our results contribute to a better understanding how the alloplasmic condition might lead to a substantial improvement in plant breeding, opening new opportunities to develop varieties more adaptable to a wide range of conditions.

GhHmgB3 deficiency deregulates proliferation and differentiation of cells during somatic embryogenesis in cotton

The proteins of high-mobility group box (HmgB) family were involved in the regulation of transcription and other DNA-dependent processes. To investigate the function of HmgB proteins during cotton somatic embryogenesis (SE), four Gossypium hirsutum HmgB genes were characterized. The gene GhHmgB3 preferentially expressed in embryonic tissues and was studied in detail. RNA interference and over-expression was used to regulate the expression of GhHmgB3 during cotton SE by transforming both hypocotyl and embryogenic calli (ECs) via Agrobacterium tumefaciens. The GhHmgB3-deficient somatic cells of hypocotyls dedifferentiated more vigorously than the control cells, but they failed to differentiate to ECs. In another case, the proliferation and differentiation of GhHmgB3-deficient ECs were significantly improved, but failed to form plantlets. Over-expression of GhHmgB3 had no significant differences in callus initiation and differentiation compared with the control cell lines. The different expression genes between the control and GhHmgB3-deficient ECs were identified by Solexa sequencing technology. The bioinformatics analysis and experimental verification revealed series of abnormal mechanism associated with β-catenin signalling. These results in response to the down-regulation of GhHmgB3 revealed series of β-catenin-related mechanisms might be responsible for the deregulation of proliferation and differentiation of cells in cotton SE.