Plant Physiol, February 2001, Vol. 125, pp. 641-651
Two Types of Pea Leghemoglobin Genes Showing Different
O2-Binding Affinities and Distinct Patterns of Spatial
Expression in Nodules1
Kazuya
Kawashima,
Norio
Suganuma,*
Masanori
Tamaoki,2 and
Hiroshi
Kouchi
Department of Life Science, Aichi University of Education, Kariya,
Aichi 448-8542, Japan (K.K., N.S., M.T.); and Department of Applied
Physiology, National Institute of Agrobiological Resources, Tsukuba,
Ibaraki 305-8602, Japan (H.K.)
Five distinct cDNA clones for leghemoglobin (Lb) were isolated from
pea (Pisum sativum) nodules. They were classified into two groups designated PsLbA and PsLbB according to sequence homology, O2-binding affinities of the recombinant proteins, and in
situ localization of the mRNAs. The PsLbB group was comprised of four cDNA clones: PsLb120-1, -8, -29, and -34. They showed a high similarity of deduced amino acid sequences and O2-binding affinities
of their recombinant proteins. Among them, the spatial expression
pattern of PsLb120-1 was investigated in great detail,
indicating that its transcripts were localized in the region from
infection zone II to the distal part of nitrogen fixation zone III in
effective nodules. PsLb5-10, which is the only cDNA clone of the PsLbA
type, differed considerably from the PsLbB type in amino acid sequence, and the recombinant protein had a higher O2-binding
affinity than those of the PsLbB type. The transcripts of
PsLb5-10 were detected throughout the central tissue of
effective nodules. However, in ineffective nodules on the pea mutant
E135 (sym13), transcripts of PsLb5-10
were restricted to the distal portion of the central tissue as well as
those of PsLb120-1. These findings indicate that the pea
genome contains two types of Lb genes and suggest that they have
different roles in the development of nitrogen-fixing symbiosis in pea nodules.
1
This work was supported in part by Special
Coordination Funds of the Science and Technology Agency of the Japanese government.
2
Present address: National Institute for Environmental
Studies, Tsukuba, Ibaraki 305-0053, Japan.
*
Corresponding author; e-mail nsuganum{at}auecc.aichi-edu.ac.jp;
fax 81-566-26-2310.
© 2001 American Society of Plant Physiologists
