Ethylene insensitivity conferred by a mutated Arabidopsis ethylene receptor gene alters nodulation in transgenic Lotus japonicus.
OBJECTIVE
Transgenics are used to demonstrate a causal relationship between ethylene insensitivity of a seedling legume plant, the level of ethylene receptor gene expression, lateral root growth and Mesorhizobium loti-induced nodule initiation.


METHODS
Lotus japonicus plants expressing the dominant etr1-1 allele of the Arabidopsis thaliana gene encoding a well-characterized mutated ethylene receptor were created by stable Agrobacterium tumefaciens transformation. Single insertion, homozygous lines were characterized for symbiotic properties.


RESULTS
Transgenic plants were ethylene insensitive as judged by the lack of the 'Triple Response', and their continued ability to grow and nodulate in the presence of inhibitory concentrations of ACC (1-aminocyclopropane-1-carboxylic acid; an ethylene precursor). Transgenic plants with high insensitivity to ACC had significantly fewer lateral roots and exhibited increased nodulation while showing no altered nitrate sensitivity or lack of systemic autoregulation. Whereas ACC-insensitive shoot growth and nodulation were observed in transformants, root growth was inhibited similarly to the wild type. Increased nodulation was caused by increased infection and a seven-fold increase in nodules developing between xylem poles. Bacteroid numbers per symbiosome increased about 1.7-fold in ethylene-insensitive plants.


CONCLUSIONS
The study further demonstrates multiple roles for ethylene in nodule initiation by influencing root cell infections and radial positioning, independent of autoregulation and nitrate inhibition of nodulation.
Lohar
Dasharath
D
ARC Centre of Excellence for Integrative Legume Research, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia.
Stiller
Jiri
J
Kam
Jason
J
Stacey
Gary
G
Gresshoff
Peter M
PM
D020561:Alphaproteobacteria / Q000254:growth & development; D000598:Amino Acids, Cyclic / Q000494:pharmacology; D029681:Arabidopsis Proteins / Q000235:genetics*; D015152:Blotting, Northern; D015139:Blotting, Southern; D005030:Ethylenes / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics; D000070116:Lotus / Q000187:drug effects* / Q000235:genetics / Q000382:microbiology*; D009154:Mutation / Q000235:genetics; D010937:Plant Growth Regulators / Q000494:pharmacology; D030821:Plants, Genetically Modified / Q000187:drug effects* / Q000235:genetics / Q000382:microbiology*; D011956:Receptors, Cell Surface / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects
D000598:Amino Acids, Cyclic; D029681:Arabidopsis Proteins; C494590:ETR1 protein, Arabidopsis; D005030:Ethylenes; D010937:Plant Growth Regulators; D011956:Receptors, Cell Surface; C023863:1-aminocyclopropane-1-carboxylic acid; C036216:ethylene