James W. Demski

Production of fertile transgenic peanut (Arachis hypogaea L.) plants using Agrobacterium tumefaciens

Fertile transgenic plants of peanut (Arachis hypogaea L. cv. New Mexico Valencia A) were produced using an Agrobacterium-mediated transformation system. Leaf section explants were inoculated with A. tumefaciens strain EHA105 harboring the binary vector pBI121 containing the genes for β-glucuronidase (GUS) and neomycin phosphotransferase II (NPTII). Approximately 10% of the shoots regenerated on selection medium were GUS-positive. Five independent transformation events resulted in the production of 52 fertile transgenic peanut plants. On average, 240 d were required between seed germination for explant preparation and the production of mature t1 seed by T0 plants. Molecular analysis of transgenic plants confirmed the stable integration of the transgenes into the peanut genome. GUS expression segregated in a 3∶1 Mendelian ratio in most T1 generation plants.

Engineered resistance to tomato spotted wilt virus in transgenic peanut expressing the viral nucleocapsid gene

The nucleocapsid gene of tomato spotted wilt virus Hawaiian L isolate in a sense orientation, and the GUS and NPTII marker genes, were introduced into peanut (Arachis hypogaea cv. New Mexico Valencia A) using Agrobacterium-mediated transformation. Modifications to a previously defined transformation protocol reduced the time required for production of transformed peanut plants. Transgenes were stably integrated into the peanut genome and transmitted to progeny. RNA expression and production of nucleocapsid protein in transgenic peanut were observed. Progeny of transgenic peanut plants expressing the nucleocapsid gene showed a 10- to 15-day delay in symptom development after mechanical inoculations with the donor isolate of tomato spotted wilt virus. All transgenic plants were protected from systemic tomato spotted wilt virus infection. Inoculated non-transformed control plants and plants transformed with a gene cassette not containing the nucleocapsid gene became systemically infected and displayed typical tomato spotted wilt virus symptoms. These results demonstrate that protection against tomato spotted wilt virus can be achieved in transgenic peanut plants by expression of the sense RNA of the tomato spotted wilt virus nucleocapsid gene

Expression and inheritance of foreign genes in transgenic peanut plants generated byAgrobacterium-mediated transformation

To evaluate and characterize the stability of traits transferred viaAgrobacterium transformation, foreign gene expression must be examined in sexually derived progeny. The objective of this study was to analyze three transgenic peanut plants, 1-10, 12-1, and 17-1, for the inheritance and expression of their foreign genes. Segregation ratios for the introduced genes in T2 plants gave either 100% or 3:1 expression of the β-glucuronidase (GUS) gene, demonstrating recovery of both homozygous and heterozygous T1 plants. Fluorometric GUS assay in T1 and T2 generations of all three plants showed that the GUS gene was stably expressed in the progeny. DNA analyses showed 100% concordance between the presence of the foreign gene and enzyme activity. Our results demonstrate that transgenes in peanut introduced byAgrobacterium can be inherited in a Mendelian manner.

Shoot organogenesis from cultured seed explants of peanut (Arachis hypogaea L.) using thidiazuron

SummaryThidiazuron (TDZ) was utilized to induce adventitious shoot formation from the hypocotyl region of cultured seed explants of peanut (Arachis hypogaea L.). Excision of the radicle from seed explants was more stimulatory to shoot initiation than removal of the epicotyl alone. Removal of both the radicle and the epicotyl from seeds resulted in a 37-fold increase in the frequency of shoot production when compared to intact seeds. Half seed explants with epicotyl and radicle removed produced the greatest number of shoots per explant. Explants from mature seeds were more responsive to TDZ than immature seed-derived explants. A 1-wk exposure to 10 μM TDZ was sufficient to stimulate the initiation of adventitious shoots that subsequently developed into plants. High frequency of shoot initiation was readily induced in a variety of genotypes ofA. hypogaea and a wild peanut (A. glabrata). Plants regenerated from shoots induced by TDZ were phenotypically normal and fertile.

Efficient plant regeneration from protoplasts of Arachis paraguariensis Chod. et Hassl. using a nurse culture method

An efficient protocol has been developed for protoplast culture and plant regeneration from wild peanut (A. paraguariensis) using a nurse culture method. Protoplasts were isolated from suspension cultures initiated from leaf-derived callus, imbedded in agarose blocks and co-cultured with nurse cells of the same species. Up to 10% of the protoplasts divided and formed compact callus colonies. The protoplast plating efficiency was correlated with both the length of the nurse cell co-cultivation period and the protoplast plating density. The optimal nurse culture duration was 14 d. The optimal plating density was 2×104 protoplasts/ml plating medium. Multiple shoots (up to 10 shoots per colony) were readily regenerated from protoplast-derived callus after transfer of callus to semi-solid modified MS medium containing 0.5 mg l-1 NAA and 1 mg l-1 BA. Plantlets with normal leaflets were obtained by rooting shoots on porous rootcubes saturated with modified MS medium containing 1 mg l-1 NAA.

Regeneration of Plants From Protoplasts of Arachis Species (Peanut)

The genus Avachis (Leguminosae), native to South America, contains 30 to 50 species in seven distinct taxonomic sections (Gregory et al. 1973; Gregory and Gregory 1979). Avachis hypogaea L., the cultivated peanut, is one of the most important protein-rich oilseed crops in the world and is cultivated on all the continents throughout the tropical, subtropical, and warmer temperate areas of the earth. Average peanut production increased by 17% from 1979 to 1989 to a total of 19.8×105metric tons even though the average world land area in peanut cultivation remained unchanged (Fletcher et al. 1992).