EAT1 transcription factor, a non-cell-autonomous regulator of pollen production, activates meiotic small RNA biogenesis in rice anther tapetum.
EAT1 transcription factor, a non-cell-autonomous regulator of pollen production, activates meiotic small RNA biogenesis in rice anther tapetum.
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DOI：
10.1371/journal.pgen.1007238
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发表时间：
2018-03
期刊：
影响因子：
4.5
通讯作者：
Nonomura KI
中科院分区：
文献类型：
--
作者：
Ono S;Liu H;Tsuda K;Fukai E;Tanaka K;Sasaki T;Nonomura KI
24核苷酸阶段次级小干扰RNA （phasiRNA）是一类独特的植物小干扰RNA，在单子房花药减数分裂早期大量表达。此前，在水稻基因组中鉴定出44个基因间区是24-nt相rna （24-PHASs）较长前体rna的位点。然而，决定这些rna时空表达的调控机制仍然是难以捉摸的。ETERNAL TAPETUM1 （EAT1）是减数分裂后花药绒毡层中诱导程序性细胞死亡（PCD）必不可少的碱性螺旋-环-螺旋（bHLH）转录因子。在本研究中，通过对eat1突变体的显微镜观察，证明了雄性减数分裂依赖于eat1的非细胞自主调节，在该突变体中，染色体异常去密的减数分裂被延迟，但以某种方式完成，最终由于异常的绒毡层PCD导致小孢子流产。在减数分裂早期和减数分裂后小孢子阶段，毡层细胞核中积累了EAT1蛋白。减数分裂的EAT1在101个位点上促进了24-PHASs rna的转录，重要的是，它还激活了DICER-LIKE5 (DCL5，之前水稻中的DCL3b) mRNA的转录，这是将双链24-PHASs加工成24-nt长度所必需的。从染色质免疫沉淀和瞬时表达分析的结果来看，另一个表达绒毡层的bHLH蛋白TDR相互作用蛋白2 （TIP2）可能参与了减数分裂小rna的生物发生。瞬时分析还表明，UNDEVELOPED TAPETUM1 (UDT1)/bHLH164是早期减数分裂中EAT1和TIP2的潜在相互作用伙伴。本研究表明，在花药绒毡层中，EAT1是触发减数分裂phasiRNA生物发生的关键调控因子之一，其他bHLH蛋白TIP2和UDT1也在这一过程中发挥了重要作用。这些bHLH蛋白的时空表达控制是协调精确减数分裂进程和随后非细胞自主花粉产生的线索。减数分裂交叉形成在亲本基因组之间洗洗同源基因，并使新的基因集能够传递给后代。交叉的频率和位置由许多遗传和表观遗传因素决定，在酵母和拟南芥中，低核小体密度区域与交叉热点有关。表观遗传染色体景观是由核小体成分、组蛋白和dna的不均匀分布修饰形成的。最近，我们发现MEL1 （ARGONAUTE5）通过组蛋白H3赖氨酸9二甲基化的显著增加，促进减数分裂染色体的大规模重塑，MEL1的缺失导致减数分裂早期停滞，很少出现交叉。在水稻花药中，mel1相关的小干扰rna （masiRNAs）由大量的减数分裂前21-nt相rna，以及低水平的24-nt重复相关siRNA和减数分裂24-nt相rna组成。在减数分裂阶段，24-nt phasiRNA的产生主要依赖于eat1。总之，我们的研究结果表明，未知的小rna介导的信号可能非细胞自主地调节雄性减数分裂，可能下游输出涉及Argonaute蛋白促进的大规模染色体重塑，而不能排除依赖于eat1但不依赖于小rna的信号的可能性。无论如何，对MEL1和绒毡层bHLH蛋白的研究将为揭示小rna介导的决定减数分裂表观遗传景观的过程提供线索。
The 24-nucleotides (nt) phased secondary small interfering RNA (phasiRNA) is a unique class of plant small RNAs abundantly expressed in monocot anthers at early meiosis. Previously, 44 intergenic regions were identified as the loci for longer precursor RNAs of 24-nt phasiRNAs (24-PHASs) in the rice genome. However, the regulatory mechanism that determines spatiotemporal expression of these RNAs has remained elusive. ETERNAL TAPETUM1 (EAT1) is a basic-helix-loop-helix (bHLH) transcription factor indispensable for induction of programmed cell death (PCD) in postmeiotic anther tapetum, the somatic nursery for pollen production. In this study, EAT1-dependent non-cell-autonomous regulation of male meiosis was evidenced from microscopic observation of the eat1 mutant, in which meiosis with aberrantly decondensed chromosomes was retarded but accomplished somehow, eventually resulting in abortive microspores due to an aberrant tapetal PCD. EAT1 protein accumulated in tapetal-cell nuclei at early meiosis and postmeiotic microspore stages. Meiotic EAT1 promoted transcription of 24-PHAS RNAs at 101 loci, and importantly, also activated DICER-LIKE5 (DCL5, previous DCL3b in rice) mRNA transcription that is required for processing of double-stranded 24-PHASs into 24-nt lengths. From the results of the chromatin-immunoprecipitation and transient expression analyses, another tapetum-expressing bHLH protein, TDR INTERACTING PROTEIN2 (TIP2), was suggested to be involved in meiotic small-RNA biogenesis. The transient assay also demonstrated that UNDEVELOPED TAPETUM1 (UDT1)/bHLH164 is a potential interacting partner of both EAT1 and TIP2 during early meiosis. This study indicates that EAT1 is one of key regulators triggering meiotic phasiRNA biogenesis in anther tapetum, and that other bHLH proteins, TIP2 and UDT1, also play some important roles in this process. Spatiotemporal expression control of these bHLH proteins is a clue to orchestrate precise meiosis progression and subsequent pollen production non-cell-autonomously. Meiotic crossover formation shuffles homologous genes between parental genomes, and enables transmission of new gene sets to the offspring. Frequency and positions of crossovers are determined by numerous genetic and epigenetic factors, and low nucleosome-density regions are associated with crossover hot spots in yeasts and Arabidopsis. The epigenetic chromosome landscape is shaped by unevenly distributed modifications of nucleosome components, histones and DNAs. Recently, we found that MEL1 (ARGONAUTE5) promotes large-scale remodeling of meiotic chromosomes with dramatic increases of histone H3 lysine 9 dimethylation, and that loss of MEL1 resulted in early meiotic arrest with few crossovers present. In rice anthers, MEL1-associating small interfering RNAs (masiRNAs) were composed of large amounts of premeiotic 21-nt phasiRNAs, plus low levels of both 24-nt repeat-associated siRNA and meiotic 24-nt phasiRNAs. Production of 24-nt phasiRNA during the meiotic stage was largely EAT1-dependent. Collectively, our findings suggest a possibility that unknown small RNA-mediated signaling regulates male meiosis non-cell-autonomously, probably a downstream output involves large-scale chromosome remodeling promoted by Argonaute proteins, while a possibility of EAT1-dependent, but small RNA-independent signaling cannot be excluded. In any cases, the studies on MEL1 and tapetal bHLH proteins will be a clue to reveal small RNA-mediated processes determining meiotic epigenetic landscape.
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影响因子：
12.3
作者：
Jones S
通讯作者：
Jones S
miRNA触发了拟南芥中转座子的广泛表观遗传激活的siRNA。
影响因子：
64.8
作者：
通讯作者：
--
DOI：
10.1073/pnas.93.15.7783
发表时间：
1996-07-23
影响因子：
11.1
作者：
Hirochika, H;Sugimoto, K;Kanda, M
通讯作者：
Kanda, M
影响因子：
7.2
作者：
Jeong, DH;An, S;An, G
通讯作者：
An, G
影响因子：
11.6
作者：
Howell, Miya D.;Fahlgren, Noah;Carrington, James C.
通讯作者：
Carrington, James C.