Scientia Agricultura Sinica ›› 2023, Vol. 56 ›› Issue (7): 1248-1259.doi: 10.3864/j.issn.0578-1752.2023.07.004

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• SPECIAL FOCUS: PANICLE DEVELOPMENT AND YIELD BREEDING IN RICE • Previous Articles     Next Articles

Mutation of PDL2 Gene Causes Degeneration of Lemma in the Spikelet of Rice

ZHAO ZiJun(), WU RuHui(), WANG Shuo, ZHANG Jun, YOU Jing, DUAN QianNan, TANG Jun, ZHANG XinFang, WEI Mi, LIU JinYan, LI YunFeng, HE GuangHua, ZHANG Ting()   

  1. College of Agronomy and Biotechnology, Southwest University/Engineering Research Center of South Upland Agriculture, Ministry of Education, Chongqing 400715
  • Received:2022-09-24 Accepted:2022-11-02 Online:2023-04-01 Published:2023-04-03

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Abstract:

【Objective】 Spikelet is a unique floral organ of the grass family. In rice, the spikelet, as the basic unit and unique structure of inflorescence, has an important impact on the yield and quality. Therefore, studying the development of rice spikelets and floral organs can provide the foundation for the formation of rice yield and quality. 【Method】 Two rice allelic mutants, polarity defect of lateral organs 2-1 and polarity defect of lateral organs 2-2 (pdl2-1 and pdl2-2) with similar mutant phenotypes were obtained using Ethyl Methane Sulfonate (EMS) mutagenesis in the indica rice maintenance line Xinong 1B. Because of their phenotypic similarity, pdl2-1 (named pdl2) was selected as the material for further analysis. Microscopic observation and paraffin sectioning techniques were used to analyze their spikelet mutant phenotypes; agronomic trait examination was used to analyze the effect of lemma on rice yield; map-based cloning were used to verify the function of PDL2; in situ hybridization and real-time fluorescence quantitative PCR (RT-qPCR) were used to analyze the expression pattern of PDL2. 【Result】 The results of the phenotypic analysis showed that the lemma of pdl2 mutant was significantly narrower and could not be closely hooked to the palea compared with that of wild type, resulting in spikelet dehiscence and partially exposed inner whorl floral organs. However, the morphology and number of stamens, pistils, and lodicules were normal. Further paraffin section results showed that the reduced volume and number of silicified and vesicular cells in the mutant lemma, as well as the reduced spacing of vascular bundles, were responsible for the significant narrowing of the width of the lemma in pdl2. Agronomic traits examined showed that the mutation in the pdl2 lemma eventually caused the seeds to be teardrop-shaped and resulted in a significant decrease in yield traits such as seed setting rate and 1000-grain weight in the pdl2 mutant. Genetic analysis and map-based cloning showed that PDL2 is a single recessive nuclear gene, which is OsDCL4 gene localized on chromosome 4. PDL2 encodes a Dicer-like protein that plays an essential role in the rice ta-siRNA synthesis pathway, and the pdl2 mutant is a novel weak allelic mutation of OsDCL4 gene. The expression pattern analysis showed that the PDL2 gene was constitutively expressed in all whorls of floral organs. Mutation of PDL2 affected the ta-siRNA synthesis and the expression of genes related to the establishment of adaxial-abaxial polarity, thus leading to the disorder of adaxial-abaxial polarity establishment in the lemma of pdl2. And the characteristics of floral organs were normal. 【Conclusion】 Mutation of lemma degeneration gene PDL2 disrupts the establishment of lemma adaxial-abaxial polarity and affects the development of lemma and the formation of yield traits.

Key words: rice (Oryza sativa L.), spikelet, lemma, map-based cloning, functional analysis

Fig. 1

Spikelet phenotypes of WT and pdl2 A-C: Stereoscope photographs of WT entire spikelet (A), spikelet stripped of palea (B), spikelet stripped of lemma and palea (C); D-F: SEM photographs of WT spikelet (D), lemma (E) and palea (F); G-I: WT spikelet cross-section (G) and local magnification of lemma (H) and palea (I); J-L: Stereoscope photographs of pdl2 entire spikelet (J), spikelet stripped of palea (K), spikelet stripped of lemma and palea (L); M-O: SEM photographs of pdl2 spikelet (M), lemma (N) and palea (O); P-R: pdl2 spikelet cross-section(P) and local magnification of lemma (Q) and palea (R). Red boxes indicate the magnification range; red asterisks indicate vascular bundles. le: Lemma; pa: Palea; rg: Rudimentary glume; sl: Sterile lemma; st: Stamen; pi: Pistil; lo: Lodicule; mrp: Marginal regions of the palea; bop: Body of the palea. The same as below. A-D, J-M Bar=2 mm; E-F, N-O Bar=400 μm; G-I, P-R Bar=200 μm"

Fig. 2

Survey of yield-related agronomic traits in WT and pdl2 A-D: Pictures of WT and pdl2 plant architecture (A), panicle architecture (B), grains (C), and brown rice (D); E-O: Statistics of agronomic traits associated with WT and pdl2. P-values were determined by the student’s t-test. *: P≤0.05; **: P≤0.01; ns: No significant difference. The same as below"

Fig. 3

Scanning electron microscope images of WT and pdl2 spikelet development at early stages A-D: WT spikelet; E-H: pdl2 lemma-degenerate spikelet. fm: Floral meristem. The same as below. Bar=1 mm"

Fig. 4

Map-based cloning of PDL2 gene A-E: Map-based cloning of the PDL2 gene; F: Mutation site prediction; G: Complementary validation of the PDL2 gene. Bar=500 μm"

Fig. 5

Expression pattern of PDL2 gene A-B: Relative expression of PDL2 gene; C-F: In situ hybridization of PDL2 gene in WT spikelets. Bar=50 μm"

Fig. 6

Expression analysis of genes characterizing floral organ development in WT and pdl2 A: Relative expression levels of lemma character gene DL; B-C: Relative expression levels of lemma and palea character genes OsMADS1 (B) and OsMADS15 (C); D: Relative expression levels of mrp character gene OsMADS6; E-F: Relative expression levels of stamen and lodicule character genes OsMADS3 (E) and OsMADS4 (F)"

Fig. 7

Expression analysis of adaxial-abaxial polarity development related genes in WT and pdl2 lemmas A-D: Relative expression levels of ARF family genes; E-I: Relative expression levels of KANADI family genes"

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