Supernumerary B chromosomes (Bs) are nonessential chromosomes that are considered genetically inert. However, the maize B carries control elements that direct its behavior, such as that of nondisjunction, during the second pollen mitosis, and affects normal A chromosomes during cell division. Recently, the maize B has been found to contain transcriptionally active sequences and to affect the transcription of genes on A chromosomes. To better understand the regulatory mechanisms underlying the maize B, we constructed two small RNA libraries from maize B73 inbred lines with and without Bs. The sequencing results revealed that 18 known microRNAs (miRNAs) were significantly differentially expressed in response to the presence of the B, and most target mRNAs were characterized as transcription factors. Moreover, three novel B-derived miRNAs were identified via stem-loop reverse transcriptase-polymerase chain reaction (RT-PCR)-based analysis, and all showed consistent B-specific expression in almost all analyzed inbred lines and in all tissue types, including leaves, roots, and pollen grains. By the use of B-10L translocations, the three B-derived miRNAs were mapped to specific B regions. The results from this study suggest that the maize B can express miRNAs and affect the expression of A-derived miRNAs, which could regulate the expression of A-located genes.

中文翻译：

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玉米B染色体能够表达微小RNA并改变源自A染色体的微小RNA的表达。

多余的B染色体（Bs）是被认为具有遗传惰性的非必需染色体。但是，玉米B携带控制元件，该控制元件在第二个花粉有丝分裂期间控制其行为，例如非分离行为，并在细胞分裂过程中影响正常的A染色体。最近，已经发现玉米B含有转录活性序列并影响A染色体上基因的转录。为了更好地了解玉米B的调控机制，我们从有和没有Bs的玉米B73自交系构建了两个小RNA库。测序结果表明，响应B的存在，有18种已知的microRNA（miRNA）显着差异表达，大多数目标mRNA被表征为转录因子。此外，通过基于茎环逆转录酶-聚合酶链反应（RT-PCR）的分析鉴定了3种新颖的B衍生miRNA，并且几乎所有分析的近交系和所有组织类型（包括叶子）都显示出一致的B特异性表达，根和花粉粒。通过使用B-10L易位，将三个B衍生的miRNA定位到特定的B区域。这项研究的结果表明，玉米B可以表达miRNA，并影响A衍生miRNA的表达，这可以调节A定位基因的表达。将三个B衍生的miRNA定位到特定的B区域。这项研究的结果表明，玉米B可以表达miRNA，并影响A衍生miRNA的表达，这可以调节A定位基因的表达。将三个B衍生的miRNA定位到特定的B区域。这项研究的结果表明，玉米B可以表达miRNA，并影响A衍生miRNA的表达，这可以调节A定位基因的表达。