The Arabidopsis genome possesses a number of sequences that are predicted to encode proteins that are similar to mammalian and yeast polyadenylation factor subunits. One of these resides on chromosome V and has the potential to encode a polypeptide related to the 100 kDa subunit of the mammalian cleavage and polyadenylation specificity factor (CPSF). This gene encodes a ca. 2400 nucleotide mRNA that in turn can be translated to yield a polypeptide that is 39% identical to the mammalian CPSF100 protein. Antibodies raised against the Arabidopsis protein recognized distinctive polypeptides in nuclear extracts prepared from pea and wheat germ, consistent with the hypothesis that the Arabidopsis protein is resident in a nuclear polyadenylation complex. Interestingly, the Arabidopsis CPSF100 was found to interact with a portion of a nuclear poly(A) polymerase. This interaction was attributable to a 60 amino acid domain in the CPSF100 polypeptide and the N-terminal 220 amino acids of the poly(A) polymerase. An analogous interaction has yet to be described in other eukaryotes. The interaction with PAP thus indicates that the plant CPSF100 polypeptide is likely part of the 3'-end processing machinery, but suggests that this complex may function differently in plants than it does in mammals and yeast.

It has been reported that the expression of the yeast poly(A) binding protein gene (PAB1) in plants leads to an induction of disease resistance responses, accompanied by alterations in the growth habit of the plant (Li et al. Plant Mol. Biol. (2000) 42 335). To capitalize on this observation, a feedback-regulated PAB1 gene was assembled and introduced into tobacco and Arabidopsis. The regulation entailed the linking of the expression of the PAB1 gene to control by the lac repressor, and by linking lac repressor expression to the disease resistance state of the plant, such that the induction of systemic defense responses by accumulation of the yeast poly(A) binding protein would turn off the expression of the PAB1 gene. Plants containing this system showed elevated and/or constitutive expression of disease-associated genes and significant resistance to otherwise pathogenic organisms. As well, they displayed a nearly normal growth habit under laboratory and greenhouse settings. These studies indicate that the expression of cytotoxic genes (such as the PAB1 gene) in plants can be controlled so that enhanced disease resistance can be achieved without significantly affecting plant growth and development.

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