Expression and evolution of functionally distinct haemoglobin genes in plants.
Haemoglobin genes have been found in a number of plant species, but the number of genes known has been too small to allow effective evolutionary inferences. We present nine new non-symbiotic haemoglobin sequences from a range of plants, including class 1 haemoglobins from cotton, Citrus and tomato, class 2 haemoglobins from cotton, tomato, sugar beet and canola and two haemoglobins from the non-vascular plants, Marchantia polymorpha (a liverwort) and Physcomitrella patens (a moss). Our molecular phylogenetic analysis of all currently known non-symbiotic haemoglobin genes and a selection of symbiotic haemoglobins have confirmed the existence of two distinct classes of haemoglobin genes in the dicots. It is likely that all dicots have both class 1 and class 2 non-symbiotic haemoglobin genes whereas in monocots we have detected only class 1 genes. The symbiotic haemoglobins from legumes and Casuarina are related to the class 2 non-symbiotic haemoglobins, whilst the symbiotic haemoglobin from Parasponia groups with the class 1 non-symbiotic genes. Probably, there have been two independent recruitments of symbiotic haemoglobins. Although the functions of the two non-symbiotic haemoglobins remain unknown, their patterns of expression within plants suggest different functions. We examined the expression in transgenic plants of the two non-symbiotic haemoglobins from Arabidopsis using promoter fusions to a GUS reporter gene. The Arabidopsis GLB1 and GLB2 genes are likely to be functionally distinct. The class 2 haemoglobin gene (GLB2) is expressed in the roots, leaves and inflorescence and can be induced in young plants by cytokinin treatment in contrast to the class 1 gene (GLB1) which is active in germinating seedlings and can be induced by hypoxia and increased sucrose supply, but not by cytokinin treatment.
Hunt
P W
PW
CSIRO Division of Plant Industry, Black Mountain, Canberra, ACT, Australia.
Watts
R A
RA
Trevaskis
B
B
Llewelyn
D J
DJ
Burnell
J
J
Dennis
E S
ES
Peacock
W J
WJ
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development; D029688:Brassica napus / Q000235:genetics; D003583:Cytokinins / Q000494:pharmacology; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D030561:Databases, Nucleic Acid; D019143:Evolution, Molecular; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D003368:Gossypium / Q000235:genetics; D006454:Hemoglobins / Q000235:genetics* / Q000502:physiology; D007541:Isopentenyladenosine; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development; D011401:Promoter Regions, Genetic / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA
D003583:Cytokinins; D018076:DNA, Complementary; D018744:DNA, Plant; D006454:Hemoglobins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C001478:N(6)-(delta(2)-isopentenyl)adenine; D007541:Isopentenyladenosine; D005966:Glucuronidase; D000225:Adenine