Activation tagging identifies a gene fromPetunia hybridaresponsible for the production of active cytokinins in plants

Abstract

SummaryCytokinins (CKs) are phytohormones that play an important role in plant growth and development. Although the ®rst naturally produced CK, zeatin, was isolated almost four decades ago, no endogenous gene has been shown to produce active CKs in planta. In an activation tagging experiment we have identi®ed a petunia line that showed CK-speci®c effects including enhanced shooting, reduced apical dominance and delayed senescence and¯owering. This phenotype correlated with the enhanced expression of a gene we labelled Sho (Shooting). Sho, which encodes a protein with homology to isopentenyl transferases (IPTs), also causes CK-speci®c effects when expressed in other plant species. In contrast to the ipt gene from Agrobacterium, which primarily increases zeatin levels, Sho expression in petunia and tobacco especially enhances the levels of certain N 6 -(D 2 -isopentenyl) adenosine (2iP) derivatives. Our data suggest that Sho encodes a plant enzyme whose activity is suf®cient to produce active CKs in plants.

Ectopic Expression of KNOTTED1-Like Homeobox Protein Induces Expression of Cytokinin Biosynthesis Genes in Rice

“…KNOX overproducer phenotypes are similar to those of transformants expressing the bacterial ipt gene (Faiss et al, 1997) and the petunia IPT gene Sho (Zubko et al, 2002), and therefore the phenotypic similarity between CK overproducers and ectopic expressers of KNOX proteins suggests that KNOX proteins are involved in a CK-related pathway in plant development. Overexpression of knox genes in transgenic plants increases CK levels (Tamaoki et al, 1997;Kusaba et al, 1998;Ori et al, 1999;Hewelt et al, 2000;Frugis et al, 2001).…”

“…The first and rate-limiting step is prenylation of adenosine 5# phosphates, such as ATP and ADP, at the N 6 -terminus with dimethylallyl diphosphate (DMAPP); this reaction is catalyzed by adenosine phosphate isopentenyltransferase (IPT). So far, plant IPT genes have been identified in dicots such as Arabidopsis (Kakimoto, 2001;Takei et al, 2001), petunia (Petunia hybrida; Zubko et al, 2002), and hop (Humulus lupulus; Sakano et al, 2004). The Arabidopsis genome encodes seven IPT genes (AtIPT1 and AtIPT3-AtIPT8; Kakimoto, 2001;Takei et al, 2001), which have different spatial expression patterns and hormone responses (Miyawaki et al, 2004;Takei et al, 2004).…”

Analysis of the SHP2 enhancer for the use of tissue specific activation tagging in Arabidopsis thaliana

“…Walden et al (1994) designed a T-DNA based activation tagging approach to identify and isolate novel genes from tobacco, and since then it has been largely applied using either T-DNA insertion strategies Ito and Meyerowitz, 2000;Lee et al, 2000;van der Graaff et al, 2000;Weigel et al, 2000;Huang et al, 2001) or transposon based approaches (Wilson et al, 1996;Marsch-Martinez et al, 2002). This technology has been applied successfully to many plant species like Arabidopsis, rice, tomato, petunia and tobacco (Weigel et al, 2000;Jeong et al, 2002;Zubko et al, 2002;Ahad et al, 2003;Mathews et al, 2003).…”

“…In some cases, the mutant displays a phenotype that can either be directly associated with the gene function of the activated gene (Zubko et al, 2002) or may provide an indication of the pathway in which the gene is involved (Kardailsky et al, 1999;Zhao et al, 2001;Yuen et al, 2003). The activation tagging method has also been used as a novel approach to isolate suppressor mutants of known mutant phenotypes (Neff et al, 1999;van der Graaff et al, 2003).…”

Controle do desenvolvimento vegetal pela interação auxina-citocinina. Uma nova abordagem baseada no estudo de mutantes de tomateiro (Solanun lycopersicum cv Micro-Tom)

“…Citocininas também regulam o desenvolvimento das sementes (RIEFLER et al, 2006) e estresse abiótico (TRAN et al, 2007). Níveis endógenos reduzidos de citocinina inibem o desenvolvimento do caule e aumentam o crescimento e ramificação das raízes , enquanto elevados níveis de citocinina podem levar a redução na dominância apical e no desenvolvimento radicular, atraso na senescência e aumento na regeneração in vitro (GAN; AMASINO, 1995;GUILFOYLE, 1992;MEDFORD et al, 1989;SMIGOCKI, 1991;ZUBKO et al, 2002). O tratamento de gemas laterais com citocinina causa quebra de dormência e o crescimento delas (PHILLIPS, 1975).…”