The functional analysis of OsTDF1 reveals a conserved genetic pathway for tapetal development between rice and Arabidopsis

doi:10.1007/s11434-015-0810-3

Science Bulletin

Volume 60, Issue 12, June 2015, Pages 1073-1082

https://doi.org/10.1007/s11434-015-0810-3 Get rights and content

Abstract

During anther development, the tapetum provides materials and nutrients for pollen development. In Arabidopsis, several transcription factors have been identified to form a genetic pathway (DYT1–TDF1–AMS–MS188–MS1) for tapetal development and function. DEFECTIVE in TAPETAL DEVELOPMENT and FUNCTION1 (TDF1) is a member of the R2R3 MYB family and is essential for early tapetum development in Arabidopsis. Here, we characterized an ortholog of Arabidopsis TDF1 in rice, OsTDF1 (LOC_Os03g18480). OsTDF1 shares 69% amino acid sequence identity with AtTDF1 in the putative MYB domain near the N-terminal region. RT-PCR and in situ hybridization show that OsTDF1 is specifically expressed in tapetal cells of rice anthers. The expression of OsTDF1 in Arabidopsis tdf1 mutant restores its fertility, suggesting that this homolog can fulfill the normal function of TDF1 in Arabidopsis. The ostdf1 knockout mutant exhibits a male-sterile phenotype. Its tapetal cells exhibit a vacuolated and hypertrophic phenotype similar to that of Arabidopsis tdf1 mutants. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays revealed OsTDF1 acts as an essential regulator for tapetum programmed cell death. The qRT-PCR analysis revealed that OsTDF1 acts downstream of UDT1 and upstream of TDR, EAT1, OsMYB103 and PTC1 in rice, suggesting that the genetic pathway for tapetum development is generally conserved between rice and Arabidopsis.

Introduction

In flowing plants, the anther is a bilaterally symmetrical structure with four lobes yielding mature pollen grains [1]. In each lobe, the cells divide and differentiate to form four distinct somatic cell layers. During meiosis, tapetal cells undergo dramatic morphological changes to acquire nutritive functions for microspores, which develop into polar secretory cells with a binuclear and condensed cytoplasm [2]. Tapetal cells play an important role in pollen development by contributing to microspore release and nutrition and sporopollenin synthesis and deposition 3., 4., 5., 6., 7.. During the late stages of anther development, tapetal cells undergo programmed cell death (PCD) to release numerous elaioplasts and cytoplasmic lipid bodies into the cavities of the exine surface as a pollen grain coating [8].

In Arabidopsis, several transcription factors (TFs) that are essential for tapetum and pollen development have been reported. DYSFUNCTIONAL TAPETUM1 (DYT1) and ABORTED MICROSPORES (AMS) are bHLH family members 9., 10.. DEFECTIVE in TAPETAL DEVELOPMENT and FUNCTION1 (TDF1) and MS188/MYB80 are two R2R3 MYB transcription factors 11., 12., 13., 14.. MALE STERILITY1 (MS1) encodes a PHD-finger family protein 15., 16.. These regulators form a genetic pathway (DYT1–TDF1–AMS–MS188–MS1) based on the analysis of double mutants and gene expression [17]. In this pathway, DYT1, TDF1 and AMS are sequentially activated to regulate early tapetum development, whereas AtMYB103 and MS1 are subsequently activated for late tapetum development and pollen wall formation. DYT1 directly regulates TDF1 for tapetum development and pollen wall formation [18].

In rice, several TFs that are essential for tapetal development and function have been identified. UNDEVELOPED TAPETUM1 (UDT1), a homolog of DYT1, plays an important role in maintaining tapetum development from early meiosis [19]. TAPETUM DEGENERATION RETARDATION (TDR), a homolog of AMS, interacts with other bHLH members, ETERNAL TAPETUM1/DELAYED TAPETUM DEGENERATION (EAT1/DTD) and bHLH142, to regulate tapetum development and degeneration via the modulation of protease expression 20., 21., 22., 23.. Sequence analysis and transgenic models have shown that Os04g39470 (OsMYB103/OsMYB80) is an ortholog of MS188 that is essential for tapetum development and pollen wall formation in rice [24]. PERSISTENT TAPETAL CELL1 (PTC1) regulates programmed tapetal development and pollen wall formation, thereby fulfilling a similar function as its homolog, MS1 [25]. In the present study, we identified the ortholog of TDF1 in rice and investigated the function of this protein in tapetum development and pollen formation. Based on these and previous results, we propose a genetic pathway for tapetum development and function in rice.

Section snippets

Mutant materials and growth conditions

The ostdf1 mutant was obtained from RISD DB (http://cbi.khu.ac.kr/RISD_DB.html). Seeds from ostdf1 and wild-type rice (Oryza sativa) were germinated for 1 week at 27 °C under continuous light and were subsequently transplanted to soil at Shanghai Normal University, located in Shanghai, China. The Arabidopsis wild-type (ecotype Ler) and tdf1 plants were grown on vermiculite at 22 °C under a 16-h light/8-h dark photoperiod.

Characterization of the mutant phenotype

The plants or flowers were photographed using a Nikon D7000 digital camera

LOC_Os03g18480 (OsTDF1) is the rice ortholog of Arabidopsis TDF1

When the amino acid sequence of Arabidopsis TDF1 was used as the query in a TBLASTN search of the rice genome, this gene showed the highest sequence similarity with the LOC_Os03g18480 in rice (O. sativa) (http://www.ncbi.nlm.nih.gov/). Conversely, when LOC_Os03g18480 was used in a TBLASTN search of the Arabidopsis genome, this gene also showed the highest sequence similarity with Arabidopsis TDF1. Therefore, LOC_Os03g18480 was designated as OsTDF1 in the present study. OsTDF1 encodes a protein

OsTDF1 is essential for tapetum development in rice

TDF1 is an essential regulator for early tapetum development in Arabidopsis [11]. Based on the sequence similarity between Arabidopsis and rice, LOC_Os03g18480 (OsTDF1) was identified as an ortholog of TDF1. Both RT-PCR analysis and in situ hybridization support the function of this protein in tapetum development in rice (Fig. 1c-e). The ostdf1 mutant exhibits abnormally vacuolated and enlarged tapetal cells that occupy the locule space during anther development (Fig. 3u-y), suggesting that

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgments

This work was supported by the grants from the Ministry of Science and Technology of China (2013CB945100), the National Natural Science Foundation of China (31100227).

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ArticleLife & Medical SciencesThe functional analysis of OsTDF1 reveals a conserved genetic pathway for tapetal development between rice and Arabidopsis

Abstract

Introduction

Section snippets

Mutant materials and growth conditions

Characterization of the mutant phenotype

LOC_Os03g18480 (OsTDF1) is the rice ortholog of Arabidopsis TDF1

OsTDF1 is essential for tapetum development in rice

Conflict of interest

Acknowledgments

Dev Biol

Mol Plant

Anther development: basic principles and practical applications

Plant Cell

The tapetum: its form, function, and possible phylogeny in Embryophyta

Plant Syst Evol

Induction of male sterility in plants by a chimeric ribonuclease gene

Nature

Studies on heteromorphic selfincompatibility systems: the cytochemistry and ultrastructure of the tapetum of Primula obconica

J Cell Sci

The remarkable biology of pollen

Plant Cell

Biogenesis and function of the lipidic structures of pollen grains

Sex Plant Reprod

Programmed cell death in plant reproduction

Plant Mol Biol

Regulation of Arabidopsis tapetum development and function by DYSFUNCTIONAL TAPETUM1 (DYT1) encoding a putative bHLH transcription factor

Development

The Arabidopsis ABORTED MICROSPORES (AMS) gene encodes a MYC class transcription factor

Plant J

Defective in Tapetal development and function 1 is essential for anther development and tapetal function for microspore maturation in Arabidopsis

Plant J

Transcription factor AtMYB103 is required for anther development by regulating tapetum development, callose dissolution and exine formation in Arabidopsis

Plant J

AtMYB103 is a crucial regulator of several pathways affecting Arabidopsis anther development

Sci China Life Sci

The MYB80 transcription factor is required for pollen development and the regulation of tapetal programmed cell death in Arabidopsis thaliana

Plant Cell

Arabidopsis MALE STERILITY1 encodes a PHD-type transcription factor and regulates pollen and tapetum development

Plant Cell

Article
Life & Medical Sciences
The functional analysis of OsTDF1 reveals a conserved genetic pathway for tapetal development between rice and Arabidopsis