Roberto Gaxiola

Assistant Professor, Plant Molecular Genetics
Department of Plant Science
University of Connecticut
Agricultural Biotechnology Laboratories
1390 Storrs Rd, U - 4163
Storrs, CT. 06269 - 4163

telephone: (860) 486- 5878, 486- 6866
fax: (860) 486- 0534
email: Roberto.Gaxiola@uconn.edu

Curriculum Vitae
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Education:

Ph.D. 1991 University of Heidelberg, Germany
M.S. 1987 Instituto Politecnico Nacional, Mexico
B.S. 1982 Unidad Guaymas, Mexico

Courses taught:

Introduction to Plant Science (Fall semesters)
Genetic Models for Crop Improvement (Spring semesters)

Current Projects:

My program focuses in two major areas of research, namely, improvement of tolerance to abiotic stresses (i.e.drought and salt) in higher plants, and regulation of cell division and morphogenesis. We are currently working with the model plant Arabidopsis thaliana.

Plant vacuoles play a central role in cellular mechanisms of adaptation to abiotic stresses such as salinity and drought. In principle, increased vacuolar solute accumulation should have a positive impact in the adaptation of plants to salinity and drought. But, how can we improve the existing solute accumulation capability of a plant vacuole?

We have engineered Arabidopsis thaliana plants to overexpress the vacuolar pyrophosphatase H+ pump, AVP1. These transgenic plants have enhanced tolerance to salinity and drought stresses. The enhanced tolerance is most easily explained by an enhanced uptake of ions into their vacuoles. Presumably, the greater AVP1 activity in vacuolar membranes provides increased H+ to drive the secondary active uptake of cations into the vacuole. Both of these transport processes will increase the membrane potential of the vacuole thereby impeding further transport of cations. Therefore, a compensatory transport of anions is expected in order to maintain electroneutrality. The resulting elevated vacuolar solute content would confer greater water retention, permitting plants to survive under conditions of low soil water potentials. Furthermore, at high Na+ concentrations, the increased H+ electrochemical gradient could also be used by Na+/H+ antiporters such as AtNHX1, thereby contributing to the Na+ sequestration within the vacuole of AVP1 transgenic plants. Presumably, any cytotoxic effects intrinsic to Na+ are mitigated by this sequestration in the vacuole.

Another phenotype of the AVP1 transgenic plants is that these plants are larger than wild type plants. The shoot and root regeneration capability of leaf explants of the trasngenic plants is dramatically enhanced when compared to wild type. A careful analysis of the cell size indicates that the transgenic AVP1 plants have normal size cells, ergo transgenic plants have more cells. These data point towards an enhanced cell division. We are currently addressing this issue. The identification of the mechanisms involved in this enhanced cell division phenotype promise to open an important avenue towards increasing plant biomass production.

My long term goals are to use genetic engineering to increase biomass production and tolerance to abiotic stresses (salinity, drought) of important crops. A more immediate goal is to understand the cellular mechanisms involved in the above phenotypes.

Selected Recent Publications:

Gaxiola, R., de Larrinoa, I. F., Villalba, J. M., and Serrano, R. (1992). A novel and conserved salt-induced protein is an important determinant of salt tolerance in yeast. Embo J 11, 3157-64.

Glaser, H. U., Thomas, D., R. Gaxiola, Montrichard, F., Surdin-Kerjan, Y., and Serrano, R. (1993). Salt tolerance and methionine biosynthesis in Saccharomyces cerevisiae involve a putative phosphatase gene. Embo J 12, 3105-10.

Serrano, R., & R. Gaxiola. (1994). Microbial models and salt stress tolerance in plants. CRC Critical Reviews in Plant Sciences 13, 121-138.

J.O. Mascorro-Gallardo, A.A. Covarrubias and R. Gaxiola "Construction of a CUP1 promoter-based vector to modulate gene expression in Saccharomyces cerevisiae. (1996) GENE 172, 169-170

Gaxiola, R., Matilde Corona and Samuel Zinker " A Halotolerant Mutant of Saccharomyces cerevisaei (1996) Journal of Bacteriology. Vol.178, No. 10. pp 2978-2981.

Gaxiola, R., Daniel Yuan, Richard Klausner and Gerald R. Fink.The Yeast CLC Chloride Channel Functions in Cation Homeostasis (1998) Proc. Natl. Acad. Sci. USA. Vol 95. pp4046-4050.

Christian Luschnig, R. Gaxiola, Paula Grisafi and Gerald R. Fink. EIR1, A Root Specific Protein Involved in Auxin Transport, is Required for Gravitropism in Arabidopsis thaliana.(1998) Genes and Development Vol12 No.14 pp 2175-2187.

Gaxiola, R., Rajini Rao, Amir Sherman, Paula Grisafi
Seth L. Alper and Gerald R. Fink. The Arabidopsis thaliana
proton transporters, AtNhx1 and Avp1, can function in cation detoxification in yeast. (1999) Proc. Natl. Acad. Sci.Vol.96 pp 1480-1485.

Zentella R, Mascorro-Gallardo JO, Van Dijck P, Folch-Mallol J, Bonini B, Van Vaeck C, R. Gaxiola, Covarrubias AA, Nieto-Sotelo J, Thevelein JM, Iturriaga G. A Seraginella lepidophylla Trehalose-6-Phosphate Synthase Complements Growth and Stress-Tolerance Defects in a Yeast tps1 Mutant. (1999) Plant Physiol Vol 119(4) pp 1473-1482.

Andrew C. Diener, R. Gaxiola, and Gerald R. Fink. Arabidopsis ALF5, a Multidrug Efflux Transporter Gene Family Member, Confers Resistance to Toxins (2001) The Plant Cell, Vol. 13, pp1625-1637.

Gaxiola, R., Jisheng, Li, Soledad Undurraga, Lien M. Dang, Gethyn J. Allen, Seth L. Alper, and Gerald R. Fink. Drought- and Salt-Tolerant Plants Results from Overexpression of the AVP1 H+-Pump. (2001) Proc. Natl. Acad. Sci Vol.98 no.20 pp11444-11449.

Gaxiola, Roberto A., Gerald R. Fink, and Kendal D. Hirschi. Genetic Manipulation of Vacuolar Proton Pumps and Transporters. (2002) Plant Physiology Vol. 129 pp. 967-973.

R. Serrano, C. Montesinos, R. Gaxiola, G. Rios, J. Forment, M. Leube, J.M. Mullet, M.A. Naranjo, M. Roldan, O. Vicente, R.A. Kanhonou, A. Rausell and R. Ros. Functional Genomics of Salt Tolerance: the Yeast Overexpression Approach. (2003) Acta Hort Vol. 609 pp 31-38.

Richard W. Mercier, Natasha M. Rabinowitz, Rashid Ali, Roberto A. Gaxiola, Gerald A. Berkowitz Yeast hygromycin sensitivity as a functional assay of cyclic nucleotide gated cation channels. (2004) Plant Physiology and Biochemistry Vol. 42 pp 529-536.

Brini, F., Gaxiola, R.A., Berkowitz, G.A., and Masmoudi, K. Cloning and characterization of wheat vacuolar cation/proton antiporter and pyrophosphatase proton pump (In press) Plant Physiology and Biochemistry.