Abstract
The symbiotic nitrogen fixation enables legume plants to grow even in the nitrogen-limiting soil. However, developing too many nodules inhibits the host plant growth because the nitrogen fixation is a high energy-consuming process. Thus the number of nodules is tightly restricted by the host plant. One of the negative regulations requires the receptor kinase HAR1 which functions in shoots, indicating that the long distance signal-mediated regulation might exist. The aim of this research is to understand the detailed molecular mechanism using the hypernodulating mutant of a model legume Lotus japonicus named too much love (tml.) Previous studies have shown that TML functions in roots, and TML and HAR1 function in the same genetic pathway. Because tml is a large deletion mutant, it would be very challenging to define the TML gene. Recent reports have shown that "Transcript-Based Gene Cloning" is effective for mutants with abolished expression of their responsible genes. Following this method, we narrow down the candidates in the deleted region. Introducing the genomic region of one candidate tends to rescue the tml mutant phenotype, suggesting this gene is a strong candidate for TML.
