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Rice false smut fungus hijacks rice lipid signalling to manipulate floret development and immunity

Nature Plants (2026)Cite this article

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Abstract

Rice false smut, caused by Ustilaginoidea virens, increases the proportion of unfilled grains and reduces pollen viability in infected rice panicles. Although the fungus adopts a flower-specific infection strategy that interferes with fertilization, the underlying molecular mechanisms remain unclear. Here we show that U. virens manipulates rice floret development and immune responses during early infection by targeting host lipid signalling. We identified secreted in xylem protein 1 (Sxp1) as a secreted apoplastic effector induced under nutrient-rich conditions and during early infection. Ectopic expression of Sxp1 in rice causes near-complete spikelet sterility and markedly reduced pollen viability. Sxp1 is a key virulence factor and interacts with the lipid transfer protein LTPL113, which binds phosphatidic acid and phosphatidylserine, and is essential for pollen development and lipid-potentiated immune outputs. Sxp1 disrupts the association between LTPL113 and lipids, thereby compromising lipid-mediated immunity and floret development. Together, our findings reveal a mechanism by which U. virens hijacks lipid signalling to manipulate floret development and suppress immunity.

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Fig. 1: Secretomic screening of Sxp1 as a key apoplastic effector in suppressing plant immunity from U. virens.
Fig. 2: U. virens Sxp1 modulates rice floret development and immune responses.
Fig. 3: LTPL113 physically interacts with Sxp1.
Fig. 4: LTPL113 is critical for rice floret development and immune responses.
Fig. 5: LTPL113 enhances rice immunity via lipid-binding activity.
Fig. 6: LTPL113 regulates pollen exine formation during reproductive development.
Fig. 7: Sxp1 disrupts LTPL113–lipid interactions to attenuate lipid-mediated immunity.
Fig. 8: Lipid-binding-defective LTPL113bsm fails to rescue developmental and immune defects in ltpl113 mutants.

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Data availability

The MS proteomics data generated in this study have been deposited in the ProteomeXchange Consortium via the MassIVE repository with the dataset identifier PXD074116 (MassIVE accession MSV000100739). All other data supporting the findings of this study are available within the article and its Supplementary Information or are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

We thank G. Yuan at Yazhouwan National Laboratory and Y. Liu at Jiangsu Academy of Agricultural Sciences for their expert assistance with the U. virens inoculation experiments. This study was supported by the National Key R&D Program of China (2024YFD1200600) and the Natural Science Foundation of China (32272492).

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Authors and Affiliations

  1. State Key Laboratory of Agricultural and Forestry Biosecurity, College of Plant Protection, Nanjing Agricultural University, Nanjing, China

    Yuandi Xu, Juan Jin, Yuhe Zhang, Xin Wang, Fan Yang, Shuang Wu, Yixin Gao, Jing-Ni Wu, Yiming Wang, Xinyu Liu, Muxing Liu, Leiyun Yang, Gang Li, Zhengguang Zhang & Haifeng Zhang

  2. College of Life Sciences, Shaanxi Normal University, Xi’an, China

    Meixiang Zhang

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Contributions

Y.X., J.J., Y.Z., X.W., F.Y., S.W., Y.G., J.-N.W., M.Z. and Y.W. performed the experiments. Y.X., J.J., Y.Z. and H.Z. analysed the data. Y.X., X.L., M.L., G.L., Z.Z. and H.Z. supervised the study and designed the experiments. Y.X., L.Y. and H.Z. wrote the paper.

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Correspondence to Haifeng Zhang.

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Extended data

Extended Data Fig. 1 U. virens infection caused unfilled grains and decreased pollen viability in rice.

a, Quantification of the unfilled grains of rice spikes infected or non-infected (CK) by U. virens in greenhouse. Red circles indicate rice false smut balls. Statistical significance was determined by two-sided Student’s t-test (P < 1.0e-15). Error bars, ± SD (n = 20 independent panicles). b, Representative micrographs showing the rice floret morphology infected by U. virens at different stages. c, Representative micrographs showing the pollen grains stained with FDA and I2-KI. Scale bars: 50 µm. d, Bar chart showing the percentage of pollen viability. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure. Error bars, ± SD (n = 4 independent biological replicates, over 50 pollen grains were analyzed per replicate).

Source Data

Extended Data Fig. 2 The flow chart for collection and identification of U. virens secretory proteins.

Proteins from YT, MM culture filtrate and infected spike filtrate were identified by LC-MS analysis, followed by bioinformatic analysis.

Extended Data Fig. 3 U. virens Sxp1 localizes to the apoplastic space and promotes Phytophthora capsici infection by suppressing plant immune response.

a, N. benthamiana leaves inoculated with P. capsici after infiltration with Agrobacterium expressing protein with signal peptide (Sxp1) and without signal peptide (Sxp1Δsp) for 36 h, and photographed at 24, 36, 48 hpi. b, Statistical analysis of the disease area following Agrobacterium-mediated expressing Sxp1 and Sxp1Δsp at 24, 36 and 48 hpi. Statistical significance was determined by two-sided Student’s t-test. Exact P values are shown in the figure. Error bars, ± SD. The number of independent leaves (n) for each group is as follows: 24 hpi (Sxp1, n = 5; Sxp1Δsp, n = 6), 36 hpi (Sxp1, n = 6; Sxp1Δsp, n = 7), and 48 hpi (Sxp1, n = 4; Sxp1Δsp, n = 7). c, N. benthamiana leaves inoculated with P. capsici after infiltration with purified Sxp1 protein (1 μM) for 24 h and photographed at 36 hpi. d, Statistical analysis of the lesion diameter under different treatments. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 10 independent leaves per treatment). e, Quantitative analysis of the fungal biomass in N. benthamiana leaves under the indicated treatments. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 3 independent infected leaves). f,g, Immunity analysis of ROS burst in N. benthamiana leaves treated with flg22, Sxp1 and flg22+Sxp1 and with Chitin, Sxp1 and Chitin+Sxp1, respectively. Error bars, ± SD (n = 3 independent leaf discs per treatment). h, Immunity analysis of ROS burst in rice leaves treated with flg22, Sxp1 and flg22+Sxp1. Error bars, ± SD (n = 3 independent leaf discs per treatment). i, Validation of the predicted signal peptide of Sxp1 by yeast invertase secretion assay. j, Localization analysis of Sxp1 in N. benthamiana leaves. Results are representative of 5 independent biological replicates. Red arrows indicate apoplastic space. Scale bars: 10 µm. k, Confocal fluorescence imaging showing Sxp1-GFP expression in rice floret tissues. Results are representative of three independent biological replicates. Scale bars: 500 µm.

Source Data

Extended Data Fig. 4 Verification of SXP1 transgenic rice lines and targeted deletion of SXP1 in U. virens.

a, RT-PCR analysis of the expression level of SXP1 in the wild type rice cultivar ZH11 and transgenic rice lines L10, L13 and L16. M: DNA marker; +: ZH11 cDNA; -: H2O. ZH11: wild type rice; L10, L13 and L16: transgenic rice lines. The ACTIN gene (LOC_Os03g61970) was used as internal control. This experiment was independently repeated twice. b, Schematic diagram of deletion strategy of SXP1 in genomic DNA. c,d, PCR and RT-PCR analysis of the SXP1 knockout mutant using F1/R1 and F2/R2 primers, respectively. The experiments were independently repeated twice. e,f, Colony morphology and diameter of the wild type, Δsxp1 and SXP1-C on PSA and MM agar plates. Photographs were taken and diameters were measured at 14 dpi. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 4 independent colonies).

Source Data

Extended Data Fig. 5 Sxp1 impairs pollen viability and suppresses the expression of pathogenesis-related (PR) genes in rice.

a, Representative micrographs showing the pollen grains stained with FDA and I2-KI. Scale bars: 50 µm. b,c, Quantification of pollen viability. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 3 independent biological replicates, over 50 pollen grains were analyzed per replicate). d, Quantitative RT-PCR analysis of PR gene expression in rice inoculated with wild-type strain (WT) or Δsxp1 at the indicated time points. dpi: days post-inoculation. Statistical significance was determined by one-way ANOVA, followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 3 independent infected panicles per time point). e, Quantitative RT-PCR analysis of PR gene expression in rice cultivar ZH11 and transgenic lines OE-SXP1 (LS13 and LS16) at rice booting stage. Statistical significance was determined by one-way ANOVA, followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure. Error bars, ± SD (n = 3 independent leaves as biological replicate).

Source Data

Extended Data Fig. 6 Identification of Sxp1-interacting proteins in rice by yeast two-hybrid assay.

a, Table summarizing candidate interacting proteins identified from a rice cDNA library using Sxp1 as bait in yeast two-hybrid (Y2H) assays. ‘Y’ indicates that the gene contains a signal peptide or a TMHMM-predicted transmembrane region, whereas ‘N’ indicates the absence of these features. ‘extr’ denotes predicted extracellular localization. b, Validation of the interaction between Sxp1 and each candidate by Y2H assay.

Extended Data Fig. 7 Verification of LTPL113 gene editing and overexpression in rice transgenic lines.

a, Sequencing analysis of the LTPL113 gene editing lines ltpl113 (M1, M2 and M4). b, Immunoblot analysis of the expression of LTPL113 in overexpression transgenic lines OE-LTPL113 (L16, L4, L5, L17, L18 and L20) using anti-Flag antibody. The experiment was independently repeated three times.

Source Data

Extended Data Fig. 8 Sxp1 disrupts LTPL113-lipid interactions to attenuate lipid-mediated immunity.

a, Pathogenicity of U. virens on rice ZS97 with or without PA, PS treatment. b,c, Quantification of false smut balls (b) and relative fungal biomass (c) in diseased rice panicles. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple comparisons test. Exact P values are shown in the figure. Error bars, ± SD. For panel b, results were quantified from n = 14 independent panicles for DMSO and n = 13 independent panicles for each of the other treatments. For panel c, relative biomass was quantified from n = 3 independent infected panicles. d,e, PA and PS content in florets of ZH11 and ltpl113. Statistical significance was determined by two-sided Student’s t-test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 3 independent biological replicates). f,g, PA and PS content in florets of ZH11 infected with wild type (WT) and Δsxp1 strains. Statistical significance was determined by one-way ANOVA followed by Tukey’s multiple comparisons test. Exact P values are shown in the figure, ns means no significance. Error bars, ± SD (n = 3 independent biological replicates).

Source Data

Extended Data Fig. 9 Verification of recombinant protein expression.

a, Recombinant LTPL113 and LTPL113bsm proteins were separated by SDS-PAGE and visualized by Coomassie brilliant blue staining. b, Recombinant Sxp1 and Sxp1bsm proteins were separated by SDS-PAGE and visualized by Coomassie brilliant blue staining. c, Immunoblot detection of LTPL113bsm expression in ltpl113 transgenic lines using anti-Flag antibody. The experiments in panels a-c were independently repeated three times.

Source Data

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Xu, Y., Jin, J., Zhang, Y. et al. Rice false smut fungus hijacks rice lipid signalling to manipulate floret development and immunity. Nat. Plants (2026). https://doi.org/10.1038/s41477-026-02260-5

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