Fruit‐specific expression of the A. tumefaciens isopentenyl transferase gene in tomato: effects on fruit ripening and defense‐related gene expression in leaves

Abstract

SummaryThis paper describes the analysis of tomato plants transformed with a chimeric gene consisting of the promoter region of a fruit specifically expressed tomato gene linked to the iptgene coding sequences from the Ti plasmid of Agrobacterium tumefaciens. The pattern of expression of this chimeric gene was found to be consistent with the expression of the endogenous fruit-specific gene and consequently, plants expressing the chimeric gene were phenotypically normal until fruit maturation and ripening. A dramatically altered fruit phenotype, islands of green pericarp tissue remaining on otherwise deep red ripe fruit, was then evident in many of the transformed plants. Cytokinin levels in transformed plant fruit tissues were 10 to lO0-fold higher than in control fruit. In the leaves of a fruitbearing transformant, despite a lack of detectable ipt mRNA accumulation, approximately fourfold higher than control leaf levels of cytokinin were detected. It is suggested that cytokinin produced in fruit is being transported to the leaves since accumulation in leaves of PR-1 and chitinase mRNAs, which encode defenserelated proteins known to be induced by cytokinin, occurred only when the transformant was reproductively active. Effects of elevated cytokinin levels on tomato fruit gene expression and cellular differentiation processes are also described.

Chromoplast Differentiation: Current Status and Perspectives

“…It was also reported that exogenous treatment with cytokinin can mimic the hp mutant phenotype ( Mustilli et al 1999 ) and that cytokinin hypersensitive Arabidopsis mutants show increased chloroplast development ( Kubo and Kakimoto 2000 ). The blotchy ripening phenotype was also induced by ectopic expression in tomato lines of the ipt gene from the Ti plasmid of Agrobacterium tumefaciens ( Martineau et al 1994 ). In this latter case, fruit displayed higher levels of cytokinin, and during ripening the fruit exhibited an altered phenotype, with green patches remaining within a deep red background.…”

Controlled Cytokinin Production in Transgenic Tobacco Using a Copper-Inducible Promoter

“…These have included promoters controlled by the external environment, e.g. light (Beinsberger et al, 1991), wounding (Smigocki et al, 1993), tetracycline (Redig et al, 1996;Faiss et al, 1997), and those related to a particular tissue or developmental state, such as fruit-specific (Martineau et al, 1994), hormone-specific (Li et al, 1992), or senescence-specific (Gan and Amasino, 1995) promoters. Generally, a higher level of control over ipt gene expression has been gained with these promoters than has been provided by the heat-shock promoters.…”

The Biotechnological Potential of Cytokinin Status Manipulation

“…The initial results in this area were not promising. For example, in tomato plants, IPT overexpression under a fruit-specific promotor produced islands of green pericarp tissue in otherwise ripe tomato fruits (Martineau et al 1994). In canola, IPT expression under the promotor of the 2S albumin seed storage gene from Arabidopsis caused IPT expression in seeds.…”