Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute (FABI), Genomics Research Institute (GRI), University of Pretoria, Private Bag X28, Pretoria, 0002, South Africa.
Plant Physiology and Improvement Unit, Laboratory of Biotechnology and Environment, Department of Plant Biology, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon.
Sci Rep. 2018 Jul 20;8(1):10983. doi: 10.1038/s41598-018-29278-w.
Secondary cell wall (SCW) deposition in Arabidopsis is regulated among others by NAC transcription factors, where SND1 chiefly initiates xylem fibre differentiation while VND6 controls metaxylem vessel SCW development, especially programmed cell death and wall patterning. The translational relevance of Arabidopsis SCW regulation theory and the utility of characterized transcription factors as modular synthetic biology tools for improving commercial fibre crops is unclear. We investigated inter-lineage gene activation dynamics for potential fibre and vessel differentiation regulators from the widely grown hardwood Eucalyptus grandis (Myrtales). EgrNAC26, a VND6 homolog, and EgrNAC61, an SND1 homolog, were transiently expressed in Arabidopsis mesophyll protoplasts in parallel to determine early and late (i.e. 7 and 14 hours post-transfection) gene targets. Surprisingly, across the time series EgrNAC26 activated only a subset of SCW-related transcription factors and biosynthetic genes activated by EgrNAC61, specializing instead in targeting vessel-specific wall pit and programmed cell death markers. Promoters of EgrNAC26 and EgrNAC61 both induced reporter gene expression in vessels of young Arabidopsis plants, with EgrNAC61 also conferring xylem- and cork cambium-preferential expression in Populus. Our results demonstrate partial conservation, with notable exceptions, of SND1 and VND6 homologs in Eucalyptus and a first report of cork cambium expression for EgrNAC61.
拟南芥次生细胞壁（SCW）的沉积受到 NAC 转录因子的调控，其中 SND1 主要启动木质部纤维的分化，而 VND6 控制木质部导管 SCW 的发育，特别是程序性细胞死亡和壁模式形成。拟南芥 SCW 调控理论的翻译相关性以及特征转录因子作为改进商业纤维作物的模块化合成生物学工具的实用性尚不清楚。我们研究了广泛种植的硬木桉树（桃金娘科）中潜在的纤维和导管分化调节因子的谱系间基因激活动态。VND6 同源物 EgrNAC26 和 SND1 同源物 EgrNAC61 被瞬时表达在拟南芥叶肉原生质体中，以平行确定早期和晚期（即转染后 7 小时和 14 小时）的基因靶标。令人惊讶的是，在整个时间序列中，EgrNAC26 仅激活了一小部分与 SCW 相关的转录因子和生物合成基因，而专门针对导管特异性壁坑和程序性细胞死亡标记物进行了靶向。EgrNAC26 和 EgrNAC61 的启动子都在年轻拟南芥植物的导管中诱导报告基因表达，EgrNAC61 还在杨树中赋予木质部和软木形成层优先表达。我们的结果表明，在桉树中 SND1 和 VND6 同源物存在部分保守性，但也存在明显的例外，并且首次报道了 EgrNAC61 对软木形成层的表达。
