Cysteine-rich receptor-like secreted protein 1 promotes intercellular infection and enhances nodulation in Aeschynomene indica

Abstract

Nitrogen-fixing bacteria establish symbiotic relationships with their host plants via two different entry systems: root hair-mediated (intracellular) entry and intercellular entry. However, the molecular mechanisms underlying the intercellular entry system have received relatively little research attention. In this study, we compared the transcriptomes of the nodules and roots of Myrica rubra, which forms an ancient type of symbiosis with Frankia via intercellular entry. We found that cysteine-rich receptor-like secreted protein 1 (CRRSP1) was highly upregulated in M. rubra nodules. We then investigated the function of MrCRRSP1 in Aeschynomene indica, which establishes symbiosis with Bradyrhizobium sp. ORS285 through an intercellular entry system. The overexpression of MrCRRSP1 and AiCRRSP1 in A. indica enhanced the nodule number and plant growth. Exogenous application of glutathione S-transferase (GST)-tagged MrCRRSP1 and AiCRRSP1 in A. indica promoted rhizobial attachment at cracks in the lateral root base, as well as rhizobial motility and biofilm formation. These results suggest that CRRSP1 promotes nodulation by enhancing rhizobial attachment to lateral root cracks. In addition to providing new insights into the molecular mechanisms underlying nodule formation through intercellular entry, this research enhances our understanding of actinorhizal plant-Frankia symbiosis.

Acknowledgments

We thank Prof. Sofie Goormachtig (Ghent University, Belgium) and Ton Bisseling (Wageningen University, Netherlands) for providing us with Bradyrhizobium sp. ORS285, Prof. Yangrong Cao (Huazhong Agricultural University, China) for providing us with Ljnfr5 seeds, Dr. Guang Chen and Dr. Fei Xu (Zhejiang Academy of Agricultural Sciences, China) for their assistance in the analysis of the M. rubra genome. This work was supported by the Key Research and Development Program of Zhejiang Province, China (2021C02064-7 and 2021C02009), the National Key Research and Development Program of China (2023YFD1902903), the National Natural Science Foundation of China (32470284 and 32270289), and the Natural Science Foundation of Zhejiang Province, China (Z25C140005).

Author contributions

Z.H. and Y.L. designed the research; Z.H. carried out most of the experiments. G.R. helped with bacterial editing techniques. X.G. helped with the RNA-seq experiment. Y.S. helped with the hair-root transformation experiment. Y.W. helped with the nodulation experiment. S.Z. and X.Q. offered plant seedlings. H.L. and J.L. contributed to the experiment design. Z.H. and Y.L. analyzed data and wrote the paper. All authors discussed the results and commented on the manuscript.

Data availability

All data are included in the main figures and supplemental figures. Any additional information required to reanalyze the data reported in this article is available from the corresponding author upon request.

Conflict of interest statement

The authors declare no conflict of interest.

Supplementary data

Supplementary data is available at Horticulture Research online.

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