Poster: Plant-pathogen interactions

Abs # 554: Antisense suppression of Bax Inhibitor (LeBI-1) in tomato leads to expression of lesion mimic phenotype and suppressed plant growth

Presenter:	Pan, Zhiqiang , zpan@olemiss.edu
Authors	Pan, Zhiqiang  (A)   Lincoln, James E. (A)   Richard, Bostock M. (A)   Gilchrist, David G. (A)
Affiliations:	(A): Department of Plant Pathology, University of California, One Shields Ave., Davis, CA 95616

Programmed cell death (PCD) plays an important role in development, stress response and disease in plants and shares many of the morphological characteristics of apoptosis as defined in animal systems. Both chemical and genetic anti-apoptotic effectors derived from animal systems have been demonstrated to block disease-related death in plant systems. AAL toxins secreted by Alternaria alternata f.sp. lycopersici induce PCD in tomato as primary determinants of the Alternaria stem canker disease . During our study of cell death associated with this disease in tomato, we cloned and studied the tomato homolog (LeBI-1) of theArabidopsis AtBI-1 Bax inhibitor that was first identified as a suppressor of Bax-induced death in yeast. In tomato, Northern blot analysis indicated that LeBI-1 is upregulated within one hour following uptake of AAL toxin by leaves. Conversely, PR1 transcripts were not detected until 12 hours after toxin uptake, indicating that signaling of LeBI-1 is upstream and prior to the expression of PR1. To study the role of LeBI in cell death, a plasmid was constructed with the LeBI-1 linked in both the sense and antisense orientation to the CaMV 35S promoter for Agrobacterium-mediated transformation. The transgenic plants with suppressed endogenous sense transcripts of LeBI-1 expressed a distinct lesion mimic phenotype early in plant development, which subsequently led to either greatly suppressed growth or death. These results suggest that the Bax inhibitor is induced rapidly in cells that are triggered to undergo PCD to limit localized death or the spread of death inducing signals, especially when death is the result of stress or disease. (Pan’s current address: USDA-ARS-NPURU, University of Mississippi, University, MS 38655)