Leghemoglobin-like sequences in the DNA of four actinorhizal plants

Abstract

A cloned cDNA partial copy of a soybean leghemoglobin mRNA was used to probe genomic DNA of four species of actinorhizal plants. Southern blot hybridization revealed the presence of sequences with homology to the leghemoglobin probe in DNA from Alnus glutinosa, Casuarina glauca, Ceanothus americanus and Elaeagnus pungens. The hybridization patterns of the restriction fragments revealed some fragment size conservation between the DNA of soybean and the DNA of four actinorhizal plants which are taxonomically unrelated to soybean or to each other. The results presented here indicate that globin gene sequences are much more widely distributed in the plant kingdom than has previously been thought. Furthermore, if sequence conservation is actually as high as the restriction fragment patterns suggest, the evolution of the DNA surrounding the globin sequences has been highly constrained.

The evolution of the actinorhizal symbiosis through phylogenetic analysis of host plants

“…Many of the plant genes normally involved in the establishment of a nitrogen-fixing symbiosis (such as those identified in the Rhizobia association, coding for flavonoids, or early and late nodulins), are also involved in other functions, and they are not exclusive to nitrogen-fixing genera or to their close non nitrogen-fixing allies (Peters et al, 1986;Doyle, 1994). This is well illustrated by the haemoglobin genes, a generally multigene family, considered at first exclusive to nodules of nitrogen-fixing members of the legume family, yet subsequently found in Parasponia (Appleby et al, 1983) and in actinorhizal taxa (Roberts et al, 1985 ;Fleming et al, 1987 ;Pathirana and Tjepkema, 1995 ;Suharjo and Tjepkema, 1995 ;Bogusz et al, 1995) as well as in non nitrogen-fixing plants (Bogusz et al, 1988 ;Taylor eta!., 1994 ), and Downloaded by [Northern Alberta Inst of Technology] at 16:54 02 February 2015 thought to have a monophyletic origin with the haemoglobin genes of animals (Landsmann et al, 1986).…”

A cereal haemoglobin gene is expressed in seed and root tissues under anaerobic conditions

“…However, the inability to demonstrate the presence of an Hb gene in monocotyledons has left open the possibility of inter-kingdom horizontal transfer to the dicots [8,31 ]. There have been no reports which unequivocally demonstrate the presence of an Hb gene in a monocotyledon [3,6], although claims of Lb-like sequences in the genomes of a number of non-legumes have appeared [36,37]. These, however, were based only on Southern blotting experiments and the results have been questioned [3].…”