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J Plant Res. 2020 Jan;133(1):109-122. doi: 10.1007/s10265-019-01159-x. Epub 2019 Dec 11.

Assessment of Polygala paniculata (Polygalaceae) characteristics for evolutionary studies of legume-rhizobia symbiosis.

Author information

1
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi, 444 8585, Japan.
2
Department of Basic Biology, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi, 444 8585, Japan.
3
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, 113 0032, Japan.
4
Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, 277-8564, Japan.
5
Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi, 464 8602, Japan.
6
Department of Biological Sciences and Kyousei Science Center for Life and Nature, Nara Women's University, Nara, 630 8506, Japan.
7
Faculty of Science, Yamagata University, Yamagata, 990 8560, Japan.
8
Astrobiology Center, Mitaka, Tokyo, 181 8588, Japan.
9
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi, 444 8585, Japan. masayosi@nibb.ac.jp.
10
Department of Basic Biology, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi, 444 8585, Japan. masayosi@nibb.ac.jp.

Abstract

Root nodule (RN) symbiosis is a mutualistic interaction observed between nitrogen-fixing soil bacteria and nodulating plants, which are scattered in only four orders of angiosperms called nitrogen-fixing clade. Most of legumes engage in RN symbiosis with rhizobia. Molecular genetic analyses with legumes and non-leguminous nodulating plants revealed that RN symbiosis utilizes early signalling components that are required for symbiosis with arbuscular mycorrhizal (AM) fungi. However detailed evolutionary processes are still largely unknown. Comparative analyses with non-nodulating species phylogenetically related to legumes could be better strategies to study the evolution of RN symbiosis in legumes. Polygala paniculata is a non-leguminous species that belongs to a family different from legumes but that is classified into the same order, Fabales. It has appropriate characteristics for cultivation in laboratories: small body size, high fertility and short lifecycles. Therefore, we further assessed whether this species is suitable as a model species for comparative studies with legumes. We first validated that the plant we obtained in Palau was truly P. paniculata by molecular phylogenetic analysis using rbcL sequences. The estimated genome size of this species was less than those of two model legumes, Lotus japonicus and Medicago truncatula. We determined conditions for cultivation in vitro and for hairy root formation from P. paniculata seedlings. It would facilitate to investigate gene functions in this species. The ability of P. paniculata to interact with AM fungi was confirmed by inoculation with Rhizophagus irregularis, suggesting the presence of early signalling factors that might be involved in RN symbiosis. Unexpectedly, branching of root hairs was observed when inoculated with Mesorhizobium loti broad host range strain NZP2037, indicating that P. paniculata has the biological potential to respond to rhizobia. We propose that P. paniculata is used as a model plant for the evolutionary study of RN symbiosis.

KEYWORDS:

Fabales; Genome size; Hairy root; Polygala paniculata; RN symbiosis; Root hair response; rbcL

PMID:
31828682
DOI:
10.1007/s10265-019-01159-x

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