Laboratory of Cell Biology, Research Institute of Forestry, Chinese Academy of Forestry, Xiangshan Road, Beijing 100091, People's Republic of China.
Planta. 2013 Jan;237(1):89-101. doi: 10.1007/s00425-012-1753-4. Epub 2012 Sep 16.
Small RNAs (sRNAs) are emerging as essential regulators of biological processes. However, several studies have reported that gymnosperms do not express appreciable amounts of 24-nt sRNAs, and conifers in particular may have a unique sRNA-silencing signature. Here, we compared the sRNA transcriptomes of Japanese larch somatic embryos (SE) and seedlings. SE sRNAs exhibited a length bias toward 24 nt, while seedlings showed a bias toward a 21-nt length. We also confirmed that larch is capable of producing 24-nt sRNAs based on a polyacrylamide gel analysis. The sRNA expression patterns varied according to developmental stage, which might be associated with Dicer-like 3 and RNA-dependent RNA polymerase2 (RDR2) levels. Our data suggest that many MIR loci that produce canonical microRNAs (miRNAs, 20-22 nt) and long sRNAs (23-26 nt) have dual functions; the latter were preferentially produced in SE compared to seedlings. However, the ratio of miRNAs to total sRNAs in seedlings was higher than in SE, and most miRNAs were upregulated in seedlings. Trans-acting small interfering RNAs (ta-siRNAs) generated from TAS3 triggered by miR390 were identified, and levels of the three detected ta-siRNAs peaked in mature embryos, which was not consistent with the lowest RDR6 level. These findings indicate that larch, and possibly other gymnosperms, shares a common sRNA pathway with other land plants, and that the sRNA distribution pattern varies according to developmental stage, which may be attributable to the expression of sRNA pathway genes.
小 RNA（sRNA）是生物过程的重要调节因子。然而，有几项研究报道称，裸子植物不会表达大量的 24nt sRNA，尤其是针叶树可能具有独特的 sRNA 沉默特征。在这里，我们比较了日本落叶松体细胞胚（SE）和幼苗的 sRNA 转录组。SE sRNA 表现出 24nt 的长度偏向，而幼苗则表现出 21nt 的长度偏向。我们还通过聚丙烯酰胺凝胶分析证实了落叶松能够产生 24nt sRNA。sRNA 的表达模式根据发育阶段而变化，这可能与 Dicer-like 3 和 RNA 依赖性 RNA 聚合酶 2（RDR2）的水平有关。我们的数据表明，许多产生典型 microRNA（miRNA，20-22nt）和长 sRNA（23-26nt）的 MIR 基因座具有双重功能；后者在 SE 中比在幼苗中更优先产生。然而，幼苗中 miRNA 与总 sRNA 的比例高于 SE，并且大多数 miRNA 在幼苗中上调。由 miR390 触发的 TAS3 产生的转座小干扰 RNA（ta-siRNA）被鉴定出来，并且在成熟胚胎中检测到的三种 ta-siRNA 的水平达到峰值，这与 RDR6 水平最低不一致。这些发现表明，落叶松，可能还有其他裸子植物，与其他陆地植物共享一个共同的 sRNA 途径，并且 sRNA 分布模式根据发育阶段而变化，这可能归因于 sRNA 途径基因的表达。
