PpNAC1, a main regulator of phenylalanine biosynthesis and utilization in maritime pine

Corresponding author: Concepción ávila

The transcriptional regulation of phenylalanine metabolism (苯丙氨酸代谢) is particularly important in conifers, long-lived species that use large amounts of carbon in wood. Here, we show that the Pinus pinaster (海岸松) transcription factor, PpNAC1, is a main regulator of phenylalanine biosynthesis and utilization. A phylogenetic analysis classified PpNAC1 in the NST proteins group and was selected for functional characterization. PpNAC1 is predominantly expressed in the secondary xylem and compression wood (应压木) of adult trees. Silencing of PpNAC1 in P. pinaster results in the alteration of stem vascular radial patterning and the down-regulation of several genes associated with cell wall biogenesis and secondary metabolism. Furthermore, transactivation (转录激活) and EMSA analyses showed that PpNAC1 is able to activate its own expression and PpMyb4 promoter, while PpMyb4 is able to activate PpMyb8, a transcriptional regulator of phenylalanine and lignin biosynthesis in maritime pine. Together, these results suggest that PpNAC1 is a functional ortholog of the Arabidopsis SND1 and NST1 genes and support the idea that key regulators governing secondary cell wall formation could be conserved between gymnosperms and angiosperms. Understanding the molecular switches controlling wood formation is of paramount importance for fundamental tree biology and paves the way for applications in conifer biotechnology.

苯丙氨酸代谢的转录调控在针叶树种中尤其重要，在多年生木本植物中需要积累大量的碳。本文的研究显示海岸松的转录因子PpNAC1基因在苯丙氨酸的生物合成及利用上起重要的调控作用。系统发育分析显示PpNAC1与NST蛋白聚为一枝，因此被选为目标基因进行功能研究。PpNAC1基因主要在成年树的次生木质部和应压木中表达。在海岸松中沉默PpNAC1基因会导致茎维管辐射模式的改变，并会下调一些与细胞壁生物合成及次生代谢相关基因的表达。此外，转录激活和EMSA分析显示PpNAC1基因能够激活其自身的表达及PpMyb4基因的启动子，而PpMyb4能够激活PpMyb8基因，同时PpMyb8基因是海岸松中苯丙氨酸和木质素生物合成的转录调控因子。综上，这些试验结果显示PpNAC1基因是拟南芥中SND1和NST1基因的同源基因，并表明被子植物和裸子植物在次生细胞壁形成相关的调控方面是保守的。理解控制木材形成的分子开关对于林木生物学基础是十分重要的，并为针叶树种的生物技术应用铺平道路。

通讯：Concepción ávila (http://www.bmbq.uma.es/index.php?option=com_content&view=article&id=65:concepcion-avila-saez&catid=16:profesor-titular-de-universidad&Itemid=113)

doi: 10.1111/pbi.12854