Seyfferth Carolin, Wessels Bernard, Jokipii-Lukkari Soile, Sundberg Björn, Delhomme Nicolas, Felten Judith, Tuominen Hannele
Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden.
Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, Umeå, Sweden.
Front Plant Sci. 2018 Mar 14;9:272. doi: 10.3389/fpls.2018.00272. eCollection 2018.
Thickening of tree stems is the result of secondary growth, accomplished by the meristematic activity of the vascular cambium. Secondary growth of the stem entails developmental cascades resulting in the formation of secondary phloem outwards and secondary xylem (i.e., wood) inwards of the stem. Signaling and transcriptional reprogramming by the phytohormone ethylene modifies cambial growth and cell differentiation, but the molecular link between ethylene and secondary growth remains unknown. We addressed this shortcoming by analyzing expression profiles and co-expression networks of ethylene pathway genes using the AspWood transcriptome database which covers all stages of secondary growth in aspen () stems. expression suggests that the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is synthesized during xylem expansion and xylem cell maturation. Ethylene-mediated transcriptional reprogramming occurs during all stages of secondary growth, as deduced from AspWood expression profiles of ethylene-responsive genes. A network centrality analysis of the AspWood dataset identified and 11 as hubs. No overlap was found between the co-expressed genes of the and hubs, suggesting target diversification and hence independent roles for these transcription factor families during normal wood formation. The hub was part of a large co-expression gene module, which contained 16 transcription factors, among them several new candidates that have not been earlier connected to wood formation and a VND-INTERACTING 2 (VNI2) homolog. We experimentally demonstrated function in ethylene signaling in . The hubs and were connected on the basis of their expression pattern and gene co-expression module composition to xylem cell expansion and secondary cell wall formation, respectively. We hereby establish data resources for ethylene-responsive genes and potential targets for EIN3D and ERF transcription factors in stem tissues, which can help to understand the range of ethylene targeted biological processes during secondary growth.
树干加粗是次生生长的结果，由维管形成层的分生组织活动完成。茎的次生生长涉及发育级联反应，导致在茎的外侧形成次生韧皮部，内侧形成次生木质部（即木材）。植物激素乙烯的信号传导和转录重编程会改变形成层生长和细胞分化，但乙烯与次生生长之间的分子联系仍不清楚。我们通过使用涵盖杨树茎次生生长所有阶段的AspWood转录组数据库分析乙烯途径基因的表达谱和共表达网络，解决了这一缺陷。表达分析表明，乙烯前体1-氨基环丙烷-1-羧酸（ACC）在木质部扩张和木质部细胞成熟过程中合成。从乙烯反应基因的AspWood表达谱推断，乙烯介导的转录重编程发生在次生生长的所有阶段。对AspWood数据集的网络中心性分析确定了 和11个 作为枢纽。在 和 枢纽的共表达基因之间未发现重叠，这表明这些转录因子家族在正常木材形成过程中具有靶标多样化，因此具有独立作用。 枢纽是一个大型共表达基因模块的一部分，该模块包含16个转录因子，其中包括几个之前未与木材形成相关联的新候选因子以及一个VND相互作用蛋白2（VNI2）同源物。我们通过实验证明了 在杨树乙烯信号传导中的功能。 枢纽 和 分别根据其表达模式和基因共表达模块组成与木质部细胞扩张和次生细胞壁形成相关联。我们在此建立了杨树茎组织中乙烯反应基因的数据资源以及EIN3D和ERF转录因子的潜在靶标，这有助于了解次生生长过程中乙烯靶向的生物学过程范围。
