Structure and function of cytokinin oxidase/dehydrogenase genes of maize, rice, Arabidopsis and other species

Abstract

Cytokinin oxidases/dehydrogenases (CKX) catalyze the irreversible degradation of the cytokinins isopentenyladenine, zeatin, and their ribosides in a single enzymatic step by oxidative side chain cleavage. To date the sequences of 17 fully annotated CKX genes are known, including two prokaryotic genes. The CKX gene families of Arabidopsis thaliana and rice comprise seven and at least ten members, respectively. The main features of CKX genes and proteins are summarized in this review. Individual proteins differ in their catalytic properties, their subcellular localization and their expression domains. The evolutionary development of cytokinin-catabolizing gene families and the individual properties of their members indicate an important role for the fine-tuned control of catabolism to assure proper regulation of cytokinin functions. The use of CKX genes as a tool in studies of cytokinin biology and biotechnological applications is discussed.

Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

“…Numbering of AtCKX genes was according to their appearance in the database, as described by Schmülling et al (2003). The genomic sequences of the AtCKX5 (MIPS gene code At1g75450; http:// mips.gsf.de/proj/thal/) and AtCKX6 (At3g63440) genes were amplified from DNA of Arabidopsis thaliana Columbia (Col-0) using the following primers: 5Ј-ggggtaccTTGATGAATCGTGAAATGAC-3Ј (forward) and 5Ј-ggggtaccCTTTCCTCTTGGTTTTGTCCTGT-3Ј (reverse) for AtCKX5 and 5Ј-cccgggTCAGGAAAAGAACCATGCTTATAG-3Ј (forward) and 5Ј-cccgggTCATGAGTATGAGACTGCCTTTTG-3Ј (reverse) for AtCKX6 (nonhomologous sequences used for cloning are shown in lowercase letters).…”

“…The Arabidopsis AtCKX gene family has seven members ( AtCKX1 to AtCKX7 ) (for review, see Schmülling et al, 2003). The predicted proteins are similar in size ( ‫ف‬ 60 kD) and have a conserved binding site for the cofactor flavin adenine dinucleotide and small highly conserved domains that may play roles in substrate recognition and electron transport.…”

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…Cytokinin oxidases degrade cytokinin (CK), suggesting that epidermal-localized CK degradation occurs in preligule cells (Houba-Hérin et al, 1999;Schmülling et al, 2003). A gene with similarity to ARABIDOPSIS THALIANA RESPONSE REGULATOR9, a type-A response regulator and negative regulator of CK signaling, was also upregulated at the blade-sheath boundary (Supplemental Figure 2E; Kiba et al, 2003;To et al, 2004).…”

Transcription Analysis of Arabidopsis Membrane Transporters and Hormone Pathways during Developmental and Induced Leaf Senescence

“…For the CK-degrading CK oxidase/dehydrogenases (CKX; Schmü lling et al, 2003) and the CK-inactivating N-and O-glucosylases, the situation is different. Of the six CKX genes on the array, only AtCKX5 is expressed at a high confidence level and increases weakly (2.1-to 2.9-fold) but continuously during NS, DIS, and DET.…”