A new class of plant homeobox genes is expressed in specific regions of determinate symbiotic root nodules.
A cDNA containing a homeobox sequence was isolated from a soybean nodule-specific expression library. This homeobox cDNA, Ndx (nodulin homeobox), represents a small gene family with at least two members in soybean (Glycine max) and three in Lotus japonicus. One complete 3304 bp Ndx cDNA from L. japonicus encodes a protein, NDX, of 958 amino acids. An unusual type of homeodomain that differs in two of the most conserved amino acid positions in the consensus sequence is located close to the C-terminal and appears to be the only DNA-binding domain. Weak Ndx gene expression in the root increases very shortly after infection with Rhizobium and remains throughout nodule development. In situ hybridizations show cell-specific expression patterns that suggest developmentally separate regions in maturing determinate nodules. Thus in the maturing nodule Ndx and leghemoglobin genes are expressed in a mutually exclusive fashion. The Ndx transcript is also detectable in the young nodule primordium. Ndx expression is not confined to the root nodule since Ndx is also expressed in shoot and root meristems, indicating that the Ndx gene products might also be involved in developmental processes in other plant tissues.
Department of Molecular and Structural Biology, University of Aarhus, Aarhus C, Denmark.
J E
JE
Jørgensen
M
M
Grønlund
N
N
Pallisgaard
K
K
Larsen
K A
KA
Marcker
E O
EO
Jensen
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D005801:Genes, Homeobox; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D017403:In Situ Hybridization; D007874:Leghemoglobin / Q000235:genetics; D019684:Magnoliopsida / Q000235:genetics*; D008565:Membrane Proteins; D005810:Multigene Family; D010940:Plant Proteins / Q000096:biosynthesis; D018517:Plant Roots / Q000235:genetics*; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000302:isolation & purification; D018749:RNA, Plant / Q000302:isolation & purification; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000235:genetics; D013559:Symbiosis / Q000235:genetics*; D014018:Tissue Distribution
D018076:DNA, Complementary; D018398:Homeodomain Proteins; D007874:Leghemoglobin; D008565:Membrane Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; C120056:ndx1 protein, plant; C045625:nodulin