Characterization and Distribution of a Maize cDNA Encoding a Peptide Similar to the Catalytic Region of Second Messenger Dependent Protein Kinases

Abstract

Maize (Zea mays) roots respond to a variety of environmental stimuli which are perceived by a specialized group of cells, the root cap. We are studying the transduction of extracellular signals by roots, particularly the role of protein kinases. Protein phosphorylation by kinases is an important step in many eukaryofic signal transduction pathways. As a first phase of this research we have isolated a cDNA encoding a maize protein similar to fungal and animal protein kinases known to be involved in the transduction of extracellular signals. The deduced sequence of this cDNA encodes a polypeptide containing amino acids corresponding to 33 out of 34 invariant or nearly invariant sequence features characteristic of protein kinase catalytic domains. The maize cDNA gene product is more closely related to the branch of serine/threonine protein kinase catalytic domains composed of the cyclic-nucleotide-and calcium-phospholipid-dependent subfamilies than to other protein kinases. Sequence identity is 35% or more between the deduced maize polypeptide and all members of this branch. The high structural similarity strongly suggests that catalytic activity of the encoded maize protein kinase may be regulated by second messengers, like that of all members of this branch whose regulation has been characterized. Northem hybridization with the maize cDNA clone shows a single 2400 base transcript at roughly similar levels in maize coleoptiles, root meristems, and the zone of root elongation, but the transcript is less abundant in mature leaves. In situ hybridization confirms the presence of the transcript in all regions of primary maize root tissue.

Regulation of Phytochrome Message Abundance in Root Caps of Maize

“…Polyadenylated RNA was purified using column chromatography with oligo dT resin according to man (1). Silver grain density was determined by manually counting grains in computer images representing equivalent areas from different regions of the root.…”

cAMP acts as a second messenger in pollen tube growth and reorientation

“…Nevertheless, the cAMP signaling pathway remains largely unknown because of the lack of evidence for its biological role and identification of a plant AC. Molecular techniques led to the identification of members of cAMP-dependent proteins like protein kinase A-like kinases (14) and CREBs (cAMP response element-binding proteins; ref. 15) but the diversity of known ACs does not facilitate their identification by homology search.…”

cDNA Sequence of PsPK5, a Protein Kinase Homolog from Pisum sativum L.

“…Relative to cAPK, PsPK5 has an additional 27 amino acids inserted between these two highly conserved regions. This insert is shorter than in any other members of the PsPK series (9) or in similar clones from bean (8), rice (8), and maize (1). Inserts can be tolerated within this region because the protein kinase encoded by the CDC7 gene of Saccharomyces cerevisiae contains an insert of 80 amino acids here (10).…”

“…This is also true of protein kinases encoded by cDNA clones from bean (8), rice (8), maize (1), and most of the partial cDNA clones from rice (5) and soybean (4).…”