Effects of Cytokinin Production under Two SAG Promoters on Senescence and Development of Tomato Plants

D. Swartzberg; N. Dai; S. Gan; R. Amasino; D. Granot

doi:10.1055/s-2006-924240

Plant Biology, Table of Contents

Plant Biol (Stuttg) 2006; 8(5): 579-586
DOI: 10.1055/s-2006-924240

Research Paper

Georg Thieme Verlag Stuttgart KG · New York

Effects of Cytokinin Production under Two SAG Promoters on Senescence and Development of Tomato Plants

D. Swartzberg¹ , N. Dai¹ , S. Gan² , R. Amasino³ , D. Granot¹

¹Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
²Department of Horticulture, Cornell University, Ithaca, NY 14853-5904, USA
³University of Wisconsin, 433 Babcock Drive, Madison, WI 53706, USA

Abstract

Two promoters of senescence-associated Arabidopsis genes, SAG12 and SAG13, were used in tomato plants to express IPT that catalyzes the rate-limiting step in cytokinin biosynthesis. Expression of these heterologous promoters in tomato plants was analyzed using the reporter gene β-glucuronidase. Both promoters are expressed in tomato leaves in a manner similar to their expression in Arabidopsis plants. The SAG12 promoter is very specific to senescing leaves, whereas the SAG13 promoter is expressed in mature leaves prior to the onset of visible senescence and its expression increases in senescing leaves. Expression of both promoters in tomato tissues other than leaves was very low. IPT expressed under the control of SAG12 and SAG13 promoters (P_SAG12::IPT and P_SAG13::IPT, respectively) resulted in suppression of leaf senescence and advanced flowering, as well as in a slight increase in fruit weight and fruit total soluble solids (TSS). However, expression of P_SAG13::IPT also led to stem thickening, short internodal distances and loss of apical dominance. In contrast to the autoregulation of P_SAG12::IPT, P_SAG13::IPT is expressed at higher levels in mature leaves. This difference is likely due to P_SAG13::IPT exhibiting two phases of expression - a senescence-independent expression prior to the onset of senescence that is not subjected to autoregulation by cytokinin, and enhanced expression throughout senescence which is autoregualted by cytokinin. This moderate different autoregulated behavior of P_SAG12::IPT and P_SAG13::IPT markedly influenced plant development, emphasizing the biological effects of cytokinin in addition to senescence inhibition.

Key words

Cytokinin - IPT - promoter - SAG - senescence - tomato

Full Text

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D. Granot

Institute of Plant Sciences
Agricultural Research Organization
The Volcani Center

P.O. Box 6

Bet Dagan 50250

Israel

Email: granot@agri.gov.il

Editor: J. T. M. Elzenga