Factors contributing to deletion within Mungbean yellow mosaic virus partial dimers in binary vectors used for agroinoculation.

Mungbean yellow mosaic virus-Vigna (MYMV) sequences cloned as partial dimers within the T-DNA of a binary vector were deleted at a high frequency upon conjugal mobilization from Escherichia coli into Agrobacterium tumefaciens. This deletion involving the genome-length viral DNA did not occur when the binary plasmid was inside E. coli and when the binary plasmid was introduced into Agrobacterium by electroporation. Deletions occurred in both DNA A and DNA B partial dimers. A minimum of 500-nt continuity on either side of the nonanucleotide in the duplicated common region is required for deletion. A. tumefaciens cells in which deletion was complete, grew as larger colonies reflecting a growth advantage. The small, slow-growing colonies eventually lost the genome-length viral sequences after a few more cycles of growth. Partial dimers in binary plasmids pGA472 and pBin19 with RK2 replicon underwent deletion while those in pPZP with pVS1 replicon did not undergo deletion. Deletion was observed in A. tumefaciens strains C58, A136, A348 and A281 with C58 chromosome background, but not in Ach5 and T37. Interestingly, deletion did not occur in A. tumefaciens strain AGL1 with a recA mutation in C58 chromosome, implying a clear role for recombination in deletion. These observations suggest the choice of Agrobacterium strains and binary vectors for agroinoculation of geminiviruses.

Analysis of an isolate of Mungbean yellow mosaic virus (MYMV) with a highly variable DNA B component.

One DNA A (KA30) and five different DNA B components (KA21, KA22, KA27, KA28 and KA34) of a geminivirus, Mungbean yellow mosaic virus-Vigna (MYMV-Vig) were cloned from a pooled sample of field-infected Vigna mungo plants from Vamban, South India. MYMV-Vig DNA A (KA30) and one of the DNA B components (KA27) exhibited 97% and 95% sequence identities, respectively, to those of MYMV reported from Thailand. However, the DNA B components KA21, KA22, KA28 and KA34 exhibited only 71 to 72% sequence identity to MYMV DNA B. Co-existence of multiple DNA B components in field-infected V. mungo was proved by Southern and PCR analyses. Each of the five DNA B components was infective together with the DNA A upon agroinoculation. Agroinoculation with mixed cultures of Agrobacterium with partial dimers of DNA A and all five DNA Bs proved that all five DNA B components can co-infect a single V. mungo plant.

Effect of Calcium on Tuberization in Potato (Solanum tuberosum L.).

Tuberization response of single-node leaf cuttings from induced potato plants (Solanum tuberosum L.) was reversed when pretreated with 5 millimolar ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) + 50 micromolar calcium ionophore (A23187) and resumed when transferred to a CaCl(2)-containing medium. Tuberization was inhibited by LaCl(3), chlorpromazine, and trifluoperazine at 5 to 10 micromolar. These results suggest a role for calcium in the tuberization process.