Radicchio Rosso lines RM3-3, RM3-4, and RM3-6 (male sterile chicory
plants) contain a ribonuclease encoded by barnase gene. The
ribonuclease, which is expressed only in the tapetum cells of the
pollen sac during anther development, blocks pollen development,
thus producing a male sterile plant. To direct the expression of
barnase to pollen cells, a pollen specific promoter, pTA 29 was
used to direct the synthesis of ribonuclease enzyme.
Expression of barnase in pollen cells apparently results in
degradation of host RNAs and blocking development of mature viable
pollen. The barnase gene encodes for an extracellular ribonuclease
protein in Bacillus amyloliquefaciens, a common soil microorganism.
B. amyloliquefaciens also contains an intracellular protein called
barstar which specifically inhibits barnase by combining with it in
a one-to-one complex. Thus, barstar is produced intracellularly by
the same organism that secretes barnase.
The second gene (bar) inserted into the Radicchio Rosso lines
RM3-3, RM3-4, and RM3-6 genome encodes for phosphinothricin
acetyltransferase (PAT) enzyme which inactivates phosphinothricin,
the active component in the herbicide glufosinate. The bar gene is
produced in the lines under the direction of Arabidospsis thaliana
PssuAra promoter and nopaline synthase termination/polyadenylation
sequences. Although these lines are tolerant to the herbicide,
hybrid progeny (the seeds that would be available to the farmers)
developed from these lines may or may not be tolerant to the
herbicide.
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