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

Abstract

Plant hormones, cytokinins (CKs), have been for a long time considered to be involved in plant responses to stress. However, their exact roles in processes linked to stress signalization and acclimatization to adverse environmental conditions are unknown. In this study, expression profiles of the entire gene families of CK biosynthetic and degradation genes in maize (Zea mays) during development and stress responses are described. Transcript abundance of particular genes is discussed in relation to the levels of different CK metabolites. Salt and osmotic stresses induce expression of some CK biosynthetic genes in seedlings of maize, leading to a moderate increase of active forms of CKs lasting several days during acclimatization to stress. A direct effect of CKs to mediate activation of stress responses does not seem to be possible due to the slow changes in metabolite levels. However, expression of genes involved in cytokinin signal transduction is uniformly down-regulated within 0.5 h of stress induction by an unknown mechanism. cis-Zeatin and its derivatives were found to be the most abundant CKs in young maize seedlings. We demonstrate that levels of this zeatin isomer are significantly enhanced during early stress response and that it originates independently from de novo biosynthesis in stressed tissues, possibly by elevated specific RNA degradation. By enhancing their CK levels, plants could perhaps undergo a reduction of growth rates maintained by abscisic acid accumulation in stressed tissues. A second role for cytokinin receptors in sensing turgor response is hypothesized besides their documented function in CK signaling.

Cytokinin Activity of cis-Zeatin and Phenotypic Alterations Induced by Overexpression of Putative cis-Zeatin-O-glucosyltransferase in Rice

“…However, expression patterns suggested that cZOGT2 might have a different physiological function from that of maize cisZOGs at the seedling stage: cZOGT2 was predominantly expressed in shoots (Figs. 5 and 6), whereas cisZOG genes were active mostly in roots (Veach et al, 2003;Vyroubalová et al, 2009).…”

“…Although recent studies with nonmodel plants suggested possible roles for cZ (Vyroubalová et al, 2009;Goggin et al, 2010;Lomin et al, 2011), its physiological significance was yet to be clarified. Our root growth assay clearly demonstrated comparable activities of cZ and tZ in the inhibition of rice seminal root elongation (Fig.…”

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.…”

Molecular cloning and expression analysis of an HINT1 homologue from maize (Zea mays L.)

“…In plant, knowledge of HINT1 protein is generally restricted to sequence analyses and the information is highly lacking, especially about the HINT1 homologue in maize. Maize (Zea mays L.) is one of the most important crop species used especially for direct human consumption and animal feed and a significant plant source for chemical feedstock (Vyroubalová et al 2009). Moreover, maize is also an important model organism for fundamental research into the inheritance and functions of genes, the physical linkage of genes to chromosomes, the mechanistic relation between cytological crossovers and recombination, origin of the nucleolus, imprinting, and transposition (Bennetzen and Hake 2009).…”