Alan B. Bennett

Professor 1117 Plant Reproductive Biology Building 530-752-1411 530-297-4496 Fax: 530-752-2278 e-mail: Lab web page

Education

B.S. University of California Plant Physiology 1977
Ph.D. Cornell University Plant Physiology 1982

Professional Experience

1993-present Associate Dean, Plant Sciences, College of Agricultural & Environmental Sciences
1991-present Professor, Department of Vegetable Crops, University of California, Davis
1990-1993 Chair, Department of Vegetable Crops, University of California, Davis
1987-1991 Associate Professor, Department of Vegetable Crops, University of California, Davis
1983-1987 Assistant Professor, Department of Vegetable Crops, University of California, Davis
1982-1983 Postdoctoral Research Associate, Section of Plant Biology, Cornell University

Research

My research program focuses on genetic modification of fruit quality, particularly as related to postharvest performance. Our research combines biochemical, genetic and molecular genetic experimental approaches to understand the biochemical basis of fruit quality parameters and then to engineer genetically modifications for their improvement. Research in my lab has focused in three primary areas of fruit quality: determinants of sugar composition and the regulation of cell wall disassembly during fruit ripening. In the area of determinants of sugar composition our goal has been to dissect the biochemical and genetic complexity of soluble sugar accumulation by identifying single biochemical processes that may contribute incrementally to enhancing total sugar levels or to enhance the proportion of particular sugars. We have studied, in detail, a single trait, originally identified in L. chmielewskii, which confers sucrose rather than hexose accumulation. To examine the underlying basis of sucrose accumulation, we have taken a genetic and biochemical approach. The genetic approach consisted of an RFLP-assisted backcross breeding program. The first crosses indicated that sucrose-accumulation was controlled by a recessive genes and subsequent segregation analysis indicated that the trait is controlled by a single recessive gene, designated sucr (Chetelat et al., 1993). Utilizing RFLP markers to map the chromosomal location of the trait and found that it is closely linked to the gene encoding acid invertase, thus providing a connection between the genetic and biochemical determinants of this trait. We subsequently demonstrated that transgenic expression of an antisense invertase gene is sufficient to confer the trait of sucrose accumulation in tomato fruit (Bennett et al., 1995). Because fructose is nearly twice as sweet as glucose, our current research is examining strategies to enhance fructose/glucose ratios in fruit. Research in the area of ripening-associated cell wall disassembly has the primary goal of identifying molecular genetic targets that may be useful in regulating the process of fruit softening. In practical terms this information could be utilized to delay softening in order to prolong storage life or modify rheological properties of the fruit to enhance processing characteristics of the fruit. The initial phase of this research focused on a single enzyme, polygalacturonase. Previously, we carried out an experiment to critically test the function of polygalacturonase by expression of a chimeric gene in a non-ripening mutant background and showed that polygalacturonase resulted in pectin solubilization and an increased susceptibility to certain pathogens but did not significantly promote fruit softening (Fischer and Bennett, 1991). Based on the above experiments, we concluded that enzymes other than polygalacturonase must also play critical roles in the softening process. Our research has been directed to examine non-pectolytic determinants of fruit softening and because hemicellulose structure is extensively modified during fruit ripening, we have focused on endo-*-1,4-glucanases as potential determinants of hemicellulose degradation during fruit ripening. To this end we isolated cDNAs encoding seven distinct, and divergent, endo-*-1,4-glucanases from tomato (Lashbrook et al., 1994). We are currently evaluating transgenic plants that express individual antisense endo-*-1,4-glucanase genes. The results to date indicate that, consistent with their pattern of overlapping expression, inhibition of expression of a single endo-b-1,4-glucanase gene has only partial effects on physiological processes such as flower abscission and cell wall disassembly in fruit.

Teaching

I teach Plants and People (PLB12), a general education course for non-majors and provides an overview of agriculture and the relationships between food production and global population. I also teach two graduate courses, Plant Membrane Biology (PLB217) and Plant Cell Biogenesis (PLB218A).

Selected References

Fischer R.L., Bennett A.B. 1991. Role of cell wall hydrolases in fruit ripening. Annu. Rev. Plant Physiol. & Plant Molec. Biol. 42:675-703.

Chetelat R., Yelle S., DeVerna J., Klann, E., Bennett A.B. 1993. Inheritance and genetic mapping of fruit sucrose accumulation in Lycopersicon chmielewskii. Plant J. 4:643-650.

Lashbrook C.L., Gonzalez-Bosch C., Bennett A.B. 1994. Two divergent endo-ß-1,4-glucanase genes exhibit overlapping expression in ripening fruit and abscission zones. Plant Cell 6:1485-1493.

Bennett A.B., Chetelat R.T., Klann E. 1995. Exotic germplasm or engineered genes: Comparison of genetic strategies to improve fruit quality. In: K-H Engel, G. Takeoka, R. Teranishi (eds), Amer. Chem. Soc. Symposium Series, Genetically Modified Foods; Safety Aspects 605:88-99.

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