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黄变直接降低了收获后大白菜的商业品质。然而，收获后大白菜叶绿素降解的机理尚不清楚。在这项工作中，我们鉴定了叶片衰老反应性NAC家族转录因子，拟南芥JUB1的同系物，在收获后的大白菜中称为BrJUB1。发现BrJUB1的表达在贮藏期间持续增加，并伴随着叶绿素分解代谢基因（CCGs）的上调）并减少叶绿素含量。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，电泳迁移率变动分析和双荧光素酶分析表明，BrJUB1结合了主要CCG启动子（包括BrNYC1，BrPAO，BrPPH1和BrSGR1）中的NAC识别序列。，并激活了它们的转录。综上所述，这些发现表明BrJUB1可能通过激活叶绿素降解，在大白菜收获后的白菜叶片衰老中起重要的调节作用。这项研究拓宽了我们对收获的大白菜和可能其他多叶蔬菜叶片衰老的分子机制的理解。