Genetic transformation of western clover (Trifolium occidentale D. E. Coombe.) as a model for functional genomics and transgene introgression in clonal pasture legume species

Production of Bovine Rotavirus VP6 Subunit Vaccine in a Transgenic Fodder Crop, Egyptian Clover (Berseem, Trifolium alexandrinum) that Elicits Immune Responses in Rabbit

Group A rotavirus causes acute gastroenteritis in young ones of animals worldwide and is responsible for a high rate of their morbidity and mortality leading to huge economic losses. Developing affordable and safer vaccine on large scale is imperative to reach cattle population worldwide for the long-term control of diarrhea. Rotavirus middle capsid protein layer, VP6, is the most immunogenic and highly conserved protein that induces immune responses against rotavirus. In the present study, bovine group A rotavirus VP6 protein has been expressed for the first time in a highly nutritious and palatable forage crop, Trifolium alexandrinum, using Agrobacterium tumefaciens-mediated stable nuclear transformation. Transgenic nature of the shoots regenerated from cotyledon explants and rooted on hygromycin-containing medium was confirmed by polymerase chain reaction (PCR), Southern blot hybridization, reverse transcription-PCR (RT-PCR) and quantitative real-time PCR (qPCR), and protein expression and quantification by Western blot and enzyme-linked immune-sorbent assay (ELISA), respectively. The transformation efficiency of 2.10% was obtained. The highest amount of VP6 protein produced in a transgenic line was 402 ng/g fresh weights (0.03% of total soluble protein). Oral feeding of transgenic leafy shoots expressing VP6 protein stimulated systemic immunity by inducing significantly higher titers of anti-VP6 serum IgG antibodies in rabbit to reduce rotavirus infection. These transgenic fodder plants offer safer vaccine produced on large scale at low cost with reduced regulatory issues to improve livestock's health and wealth. These plants would be used as alternative to the current live attenuated vaccines to protect young calves against rotavirus infection.

Optimization of Protocols for the Induction of Callus and Plant Regeneration in White Clover (Trifolium repens L.)

White clover is a widely grown temperate legume forage with high nutritional value. Research on the functional genomics of white clover requires a stable and efficient transformation system. In this study, we successfully induced calluses from the cotyledons and leaves of 10 different white clover varieties. The results showed that the callus formation rate in the cotyledons did not vary significantly among the varieties, but the highest callus formation rate was observed in 'Koala' leaves. Subsequently, different concentrations of antioxidants and hormones were tested on the browning rate and differentiation ability of the calluses, respectively. The results showed that the browning rate was the lowest on MS supplemented with 20 mg L^-1 AgNO₃ and 25 mg L^-1 VC, respectively, and the differentiation rate was highest on MS supplemented with 1 mg L^-1 6-BA, 1 mg L^-1 KT and 0.5 mg L^-1 NAA. In addition, the transformation system for Agrobacterium tumefaciens-mediated transformation of 4-day-old leaves was optimized to some extent and obtained a positive callus rate of 8.9% using green fluorescent protein (GFP) as a marker gene. According to our data, by following this optimized protocol, the transformation efficiency could reach 2.38%. The results of this study will provide the foundation for regenerating multiple transgenic white clover from a single genetic background.

Knock-down of transcript abundance of a family of Kunitz proteinase inhibitor genes in white clover (Trifolium repens) reveals a redundancy and diversity of gene function

The transcriptional regulation of four phylogenetically distinct members of a family of Kunitz proteinase inhibitor (KPI) genes isolated from white clover (Trifolium repens; designated Tr-KPI1, Tr-KPI2, Tr-KPI4 and Tr-KPI5) has been investigated to determine their wider functional role. The four genes displayed differential transcription during seed germination, and in different tissues of the mature plant, and transcription was also ontogenetically regulated. Heterologous over-expression of Tr-KPI1, Tr-KPI2, Tr-KPI4 and Tr-KPI5 in Nicotiana tabacum retarded larval growth of the herbivore Spodoptera litura, and an increase in the transcription of the pathogenesis-related genes PR1 and PR4 was observed in the Tr-KPI1 and Tr-KPI4 over-expressing lines. RNA interference (RNAi) knock-down lines in white clover displayed significantly altered vegetative growth phenotypes with inhibition of shoot growth and a stimulation of root growth, while knock-down of Tr-KPI1, Tr-KPI2 and Tr-KPI5 transcript abundance also retarded larval growth of S. litura. Examination of these RNAi lines revealed constitutive stress-associated phenotypes as well as altered transcription of cellular signalling genes. These results reveal a functional redundancy across members of the KPI gene family. Further, the regulation of transcription of at least one member of the family, Tr-KPI2, may occupy a central role in the maintenance of a cellular homeostasis.

Heterologous expression of AtMYB12 in kale (Brassica oleracea var. acephala) leads to high flavonol accumulation

Overexpression of Arabidopsis AtMYB12 transcription factor greatly increases the total phenolic and flavonol content in transgenic kale leaves. Flavonoids are a diverse group of plant secondary metabolites exhibiting a number of health-promoting effects. There has been a growing interest to develop biotechnological methods for the enhanced production of flavonoids in crop plants. AtMYB12 is an Arabidopsis transcription factor which specifically activates flavonol synthesis and its overexpression has led to increased flavonol accumulation in several transgenic plants. In the present study, AtMYB12 was overexpressed in a commercial cultivar of kale and the transgenic plants were tested both in in vitro and in semi-field conditions in cages under natural light. Using this method, a severalfold increase in both total phenolics content and flavonol accumulation was achieved. This study provides a reliable and efficient transformation protocol for kale and suggests the potential of this flavonol-enriched vegetable for the production of kaempferol.