Zeatin is a naturally occurring cytokinin. Biosynthesis and
metabolism studies of zeatin have been directed mostly at the
trans
isomer, although
cis
-zeatin and its
riboside occur as major components in some plant species. It is not
known whether parallel regulatory pathways exist for the two isomers.
Based on the sequence of the gene
ZOG1
encoding a
trans
-zeatin
O
-glucosyltransferase from
Phaseolus
(EC
2.4.1.203
), a
cis
-zeatin-specific
O
-glucosyltransferase
was isolated from maize. This gene,
cisZOG1
, contains an
ORF of 1,401 nucleotides encoding a protein of 51.1 kDa with 41%
identity to the
Phaseolus
ZOG1 protein. Unexpectedly,
the maize enzyme recognizes as substrates
cis
-zeatin and
UDP-glucose but not
cis
-ribosylzeatin,
trans
-zeatin, or
trans
-ribosylzeatin.
This finding indicates the existence of cis-specific regulatory
elements in plants and suggests that
cis
-zeatin and
derivatives may be more important in cytokinin homeostasis than
currently recognized.
泽古素是一种天然存在的细胞分裂素。泽古素的生物合成和代谢研究主要针对顺式异构体,尽管反式-泽古素及其核苷酸在某些植物物种中是主要成分。目前不清楚这两种异构体是否存在并行的调节途径。基于编码来自菜豆(Phaseolus)的顺式-泽古素O-葡萄糖苷转移酶(EC 2.4.1.203)的基因ZOG1序列,从玉米中分离出了一种顺式-泽古素特异性O-葡萄糖苷转移酶。这个基因cisZOG1包含一个由1401个核苷酸编码的蛋白质,分子量为51.1 kDa,与菜豆ZOG1蛋白质的相似度为41%。出乎意料的是,玉米酶识别的底物是反式-泽古素和UDP-葡萄糖,而不是反式-核苷基泽古素、顺式-泽古素或顺式-核苷基泽古素。这一发现表明植物中存在顺式特异性调节元素,并暗示着cis-泽古素及其衍生物可能在细胞分裂素稳态中比目前认为的更为重要。