Maize cytokinin oxidase genes: differential expression and cloning of two new cDNAs

Abstract

Cytokinin oxidases (CKOs) play a major role in the regulation of hormone levels in plants by irreversibly degrading cytokinins. Two new cDNAs from maize (CKO2 and CKO3) were cloned and CKO activity of a recombinant CKO3 enzyme was demonstrated. CKO2 and CKO3 encode flavoproteins with 93% identity among each other compared with 45% identity with CKO1. The respective genes were mapped to BIN 3.05/06 and BIN 8.06 which belong to duplicated regions of the maize genome. For a better understanding of the role of CKO2 and CKO3 in maize development, their expression profiles were analysed in different organs and during kernel development via semi-quantitative RT-PCR. Different spatial and temporal expression patterns were observed for the two genes, as well as for CKO1 and two additional genes CKO4 and CKO5. CKO2 to CKO5 genes were mainly expressed in vegetative tissues, with unique expression patterns. CKO1 was most strongly expressed in the kernel. All five genes were expressed at early stages of kernel development, a period when a peak in cytokinin levels and a high cell division rate in the endosperm have been described. However, each gene had its own expression profile with a major difference concerning the onset of expression.

Structure and Function of Nucleoside Hydrolases from Physcomitrella patens and Maize Catalyzing the Hydrolysis of Purine, Pyrimidine, and Cytokinin Ribosides

“…We focused on two model plant organisms, the moss P. patens and maize, due to the availability of detailed information on cytokinin metabolism in both species (Massonneau et al, 2004;von Schwartzenberg, 2009;Vyroubalová et al, 2009). The genome databases for the moss P. patens (www.phytozome.net, version 9.1) and maize (www.maizesequence.org, version 5b.60) indicate that these species contain three and five NRH genes, respectively.…”

Characterization of New Maize Genes Putatively Involved in Cytokinin Metabolism and Their Expression during Osmotic Stress in Relation to Cytokinin Levels

“…Homology searches were done by BLASTn software on the maize genome sequencing project database (http://www.maizesequence.org/index.html) with currently known sequences as templates (Massonneau et al, 2004;Brugière et al, 2008) and rice orthologous sequences (Sakamoto et al, 2006;Hirose et al, 2007). BAC clones in the database cover almost 95% of information of the rough draft of the maize genome, as was announced on December 2008.…”

“…Two maize CKX genes were proved to encode functional enzymes (CKX1 and CKX3; Houba-Hérin et al, 1999;Morris et al, 1999;Massonneau et al, 2004), and expression profiles of another three genes were analyzed (CKX2, CKX4, and CKX5; Massonneau et al, 2004). Data mining from the maize genome database revealed another eight sequences showing ORFs homologous to annotated CKX proteins.…”

“…The irreversible degradation of free CK bases and their derivatives is catalyzed by CK oxidase/dehydrogenases (CKXs), encoded as well by a small gene family. Nevertheless, there is evidence for several maize CKXs (Massonneau et al, 2004); only one member of maize CKX enzymes, ZmCKX1, was studied in detail in connection with plant stress responses (Brugière et al, 2003). Elevated levels of ZmCKX1 transcript were observed in developing kernels during various abiotic stresses.…”

Cytokinins and Their Possible Role in Seed Size and Seed Mass Determination in Maize

“…Degradation and reversible/irreversible inactivation are key regulators of CK levels. Several maize CK dehydrogenase genes (Ckx) are expressed in the caryopsis pedicel region, endosperm and embryo (Massonneau et al, 2004;Šmehilová et al, 2009;Vyroubalová et al, 2009), and their corresponding protein products irreversibly cleave the N 6 -side chain from the main purine ring (Massonneau et al, 2004). Recently, the importance of conjugation has also been described.…”