IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Title Lotus japonicus nodulates when it sees red.
Authors Akihiro Suzuki 1 , Lalith Suriyagoda 1 , Tamaki Shigeyama 1 , Akiyoshi Tominaga 1 , Masayo
Sasaki 1 , Yoshimi Hiratsuka 1 , Aya Yoshinaga 1 , Susumu Arima 1 , Sakae Agarie 1 , Tatsuya
Sakai 2 , Sayaka Inada 2 , Yusuke Jikumaru 2 , Yuji Kamiya 2 , Toshiki Uchiumi 3 , Mikiko Abe 3 ,
Masatsugu Hashiguchi 4 , Ryo Akashi 4 , Shusei Sato 5 , Takakazu Kaneko 5 , Satoshi Tabata 5 &
Ann M. Hirsch 6
Poster Board Number 16
1 Faculty of Agriculture, Saga University, Honjyo-machi, Saga, Saga 840-8502, Japan.
2 RIKEN Plant Science Center, Yokohama, Kanagawa 230-0045, Japan.
3 Faculty of Science, Kagoshima University, Korimoto, Kagoshima 890-0065, Japan.
4 Frontier Science Research Center, University of Miyazaki, Miyazaki, Miyazaki 889-2192,
Japan.
5 Kazusa DNA Research Institute, Kisarazu, Chiba 292-0812, Japan.
6 Department of Molecular, Cell and Developmental Biology and Molecular Biology Institute,
University of California-Los Angeles, California, USA.
Light is critical for supplying carbon to the energetically expensive, nitrogen-fixing symbiosis between legumes
and rhizobia. In this study, we show that Phytochrome B (PHYB) is part of the monitoring system to detect
suboptimal light conditions, which normally suppress Lotus japonicus nodule development in response to
inoculation of Mesorhizobium loti. We found that the number of nodules produced by phyB mutants of L.
japonicus is significantly reduced compared to that of wild-type MG20. To explore another cause other than
photoassimilates, the possibility of local control was investigated by grafting experiments. The results showed
that shoot genotype, and not the root genotype is responsible for root nodule formation. To explore causes by
systemic regulation, we moved wild-type MG20 plants from white light to conditions differing in the ratios of low
or high red (R)/far-red (FR) light. In low R/FR light, the number of root nodules on MG20 plants dramatically
decreased compared to plants grown in high R/FR even though photoassimilate content was higher for plants
grown under low R/FR. We found that the expression of jasmonic acid (JA)-responsive genes was decreased in
both low R/FR light-grown MG20 and in white light-grown phyB mutant plants. Indeed Endogenous concentration
of JA-Ile was decreased in phyB mutant. Moreover, both infection thread formation and root nodule formation
were positively influenced by JA treatment of wild-type plants grown in low R/FR light and of white light-grown
phyB mutants. These results indicate that root nodule formation is photomorphogenetically controlled by sensing
the R/FR ratio through JA signaling.
131
2011