ABSTRACT

Leaf yellowing caused by chlorophyll degradation directly reduces the commercial quality of post-harvest Chinese flowering cabbage. However, the mechanism of chlorophyll degradation in post-harvest Chinese flowering cabbage remains unclear. In this work, we identified a leaf senescence-responsive NAC family transcription factor, a homologue of JUB1 in Arabidopsis, termed BrJUB1 in post-harvest Chinese flowering cabbage. The expression of BrJUB1 was found to increase continuously during storage time, accompanied by an upregulation of chlorophyll catabolic genes (CCGs) and reduced chlorophyll content. Subcellular localisation and transactivation analyses in tobacco revealed that BrJUB1 possessed two characteristics of transcription factors: nuclear localisation and transactivation of gene activity. More importantly, electrophoretic mobility shift assay and dual-luciferase analysis demonstrated that BrJUB1 bound to NAC recognition sequence in the promoters of major CCGs including BrNYC1, BrPAO, BrPPH1 and BrSGR1, and activated their transcription. Taken together, these findings show that BrJUB1 might act as an important regulator in leaf senescence of post-harvest Chinese flowering cabbage through activating chlorophyll degradation. This study expands our understanding of molecular mechanisms involved in leaf senescence of harvested Chinese cabbage and possibly other leafy vegetables.

摘要

叶绿素降解引起的叶片黄化直接降低了大白菜收获后的商业品质。然而，大白菜收获后叶绿素降解的机制尚不清楚。在这项工作中，我们鉴定了一种叶片衰老响应 NAC 家族转录因子，它是拟南芥中 JUB1 的同源物，在收获后的大白菜中称为 BrJUB1。发现 BrJUB1 的表达在储存期间持续增加，伴随着叶绿素分解代谢基因 ( CCGs)的上调) 并降低叶绿素含量。烟草中的亚细胞定位和反式激活分析表明，BrJUB1 具有转录因子的两个特征：核定位和基因活性的反式激活。更重要的是，电泳迁移率变化测定和双荧光素酶分析表明，BrJUB1 与主要CCG启动子中的 NAC 识别序列结合，包括BrNYC1、BrPAO、BrPPH1和BrSGR1，并激活它们的转录。综上所述，这些发现表明 BrJUB1 可能通过激活叶绿素降解在大白菜收获后的叶片衰老中发挥重要调节作用。这项研究扩展了我们对收获的大白菜和可能的其他叶类蔬菜叶片衰老的分子机制的理解。