The transcription factor NODULE INCEPTION (NIN) has been studied extensively for its multiple roles in root nodule symbiosis within plants of the nitrogen-fixing clade (NFC) that associate with soil bacteria, such as rhizobia and Frankia. However, NIN homologs are present in plants outside the NFC, suggesting a role in other developmental processes. Here, we show that the biofuel crop Populus sp., which is not part of the NFC, contains eight copies of NIN with diversified protein sequence and expression patterns. Lipo-chitooligosaccharides (LCOs) are produced by rhizobia and a wide range of fungi, including mycorrhizal ones, and act as symbiotic signals that promote lateral root formation. RNAseq analysis of Populus sp. treated with purified LCO showed induction of the PtNIN2 subfamily. Moreover, the expression of PtNIN2b correlated with the formation of lateral roots and was suppressed by cytokinin treatment. Constitutive expression of PtNIN2b overcame the inhibition of lateral root development by cytokinin under high nitrate conditions. Lateral root induction in response to LCOs likely represents an ancestral function of NIN retained and repurposed in nodulating plants, as we demonstrate that the role of NIN in LCO-induced root branching is conserved in both Populus sp. and legumes. We further established a visual marker of LCO perception in Populus sp. roots, the putative sulfotransferase PtSS1 that can be used to study symbiotic interactions with the bacterial and fungal symbionts of Populus sp.

中文翻译：

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NODULE INCEPTION 的 LCO 响应同源物正向调节杨属侧根的形成。

转录因子 NODULE INCEPTION (NIN) 因其在与根瘤菌和 Frankia 等土壤细菌相关的固氮进化枝 (NFC) 植物根瘤共生中的多种作用而得到了广泛的研究。然而，NIN 同源物也存在于 NFC 之外的植物中，表明其在其他发育过程中发挥作用。在这里，我们证明生物燃料作物杨属（Populus sp.）不属于NFC的一部分，含有八个NIN拷贝，具有多样化的蛋白质序列和表达模式。脂壳低聚糖 (LCO) 由根瘤菌和多种真菌（包括菌根真菌）产生，作为促进侧根形成的共生信号。杨属物种的 RNAseq 分析。用纯化的 LCO 处理显示出 PtNIN2 亚家族的诱导。此外，PtNIN2b 的表达与侧根的形成相关，并受到细胞分裂素处理的抑制。PtNIN2b的组成型表达克服了高硝酸盐条件下细胞分裂素对侧根发育的抑制。对 LCO 的侧根诱导可能代表了 NIN 在结瘤植物中保留和重新利用的祖先功能，因为我们证明 NIN 在 LCO 诱导的根分枝中的作用在两种杨属中都是保守的。和豆类。我们进一步建立了杨属 LCO 感知的视觉标记。根，假定的磺基转移酶 PtSS1，可用于研究杨属细菌和真菌共生体的共生相互作用。