J Integr Plant Biol. ›› 2023, Vol. 65 ›› Issue (9): 2218-2236.DOI: 10.1111/jipb.13508

• Plant Reproductive Biology • Previous Articles    

Rice pollen-specific OsRALF17 and OsRALF19 are essential for pollen tube growth

Eui‐Jung Kim1†, Ji‐Hyun Kim2†, Woo‐Jong Hong3, Eun Young Kim4, Myung‐Hee Kim4,5, Su Kyoung Lee1, Cheol Woo Min6, Sun Tae Kim6, Soon Ki Park4, Ki‐Hong Jung1,7* and Yu‐Jin Kim2*   

  1. 1. Graduate School of Green Bio‐Science & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Republic of Korea;
    2. Department of Life Science and Environmental Biochemistry, Life and Industry Convergence Research Institute, Pusan National University, Miryang 50463, Republic of Korea;
    3. Department of Smart Farm Science, Kyung Hee University, Yongin 17104, Republic of Korea;
    4. School of Applied Biosciences, Kyungpook National University, Daegu 41566, Republic of Korea;
    5. Genomics Division, Department of Agricultural Bio‐Resources, National Institute of Agricultural Sciences, Rural Development Administration, Jeonju 54874, Republic of Korea;
    6. Department of Plant Bioscience, Pusan National University, Miryang 50463, Republic of Korea;
    7. Research Center for Plant Plasticity, Seoul National University, Seoul 08826, Republic of Korea
    These authors contributed equally to this manuscript.
    *Correspondences: Yu‐Jin Kim (yjkim2020@pusan.ac.kr, Dr. Kim is fully responsible for the distribution of all materials associated with this article); Ki‐Hong Jung (khjung2010@khu.ac.kr)
  • Received:2022-10-25 Accepted:2023-05-16 Online:2023-05-17 Published:2023-09-01

Abstract: Pollen tube growth is essential for successful double fertilization, which is critical for grain yield in crop plants. Rapid alkalinization factors (RALFs) function as ligands for signal transduction during fertilization. However, functional studies on RALF in monocot plants are lacking. Herein, we functionally characterized two pollen-specific RALFs in rice (Oryza sativa) using multiple clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9-induced loss-of-function mutants, peptide treatment, expression analyses, and tag reporter lines. Among the 41 RALF members in rice, OsRALF17 was specifically expressed at the highest level in pollen and pollen tubes. Exogenously applied OsRALF17 or OsRALF19 peptide inhibited pollen tube germination and elongation at high concentrations but enhanced tube elongation at low concentrations, indicating growth regulation. Double mutants of OsRALF17 and OsRALF19 (ralf17/19) exhibited almost full male sterility with defects in pollen hydration, germination, and tube elongation, which was partially recovered by exogenous treatment with OsRALF17 peptide. This study revealed that two partially functionally redundant OsRALF17 and OsRALF19 bind to Oryza sativa male-gene transfer defective 2 (OsMTD2) and transmit reactive oxygen species signals for pollen tube germination and integrity maintenance in rice. Transcriptomic analysis confirmed their common downstream genes, in osmtd2 and ralf17/19. This study provides new insights into the role of RALF, expanding our knowledge of the biological role of RALF in regulating rice fertilization.

Key words: CRISPR-Cas9, CrRLK1L, monocot, Oryza sativa, pollen tube growth, rapid alkalinization factor (RALF)

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