Bioengineering College, Chongqing University, Chongqing, 400044, China.
Key Laboratory of Biorheological Science and Technology, Ministry of Education, Chongqing University, Chongqing, 400044, China.
Physiol Plant. 2020 Jun;169(2):143-155. doi: 10.1111/ppl.13068. Epub 2020 Feb 15.
Leaf senescence is a highly-programmed developmental process during the plant life cycle. Cytokinin (CK) has been widely acknowledged as a negative regulator to delay leaf senescence. MiRNAs play key roles in a variety of developmental and physiological processes through negatively regulating their target gene expression. However, to date, the roles of microRNAs (miRNAs) in CK biosynthesis remain unclear, and the knowledge on miRNA regulation of leaf senescence is still very limited. Isopentenyltransferases (IPTs) catalyze the initial and rate-limiting step of CK biosynthesis in higher plants. Our previous work uncovered that silencing of SlIPT4 expression in tomato resulted in premature leaf senescence. Here, we identified a novel tomato miRNA, SlymiR208, which regulates the expression of SlIPT2 and SlIPT4 at the post-transcriptional level. SlymiR208 expression is ubiquitous in tomato and exhibits an opposite transition to its target transcripts in aged leaf. SlymiR208 overexpression in tomato sharply reduced the transcript levels of SlIPT2 and SlIPT4, and the concentrations of endogenous CKs in leaves. The early leaf senescence caused by SlymiR208 overexpression was consistent with the phenotype of SlIPT4-silenced lines. The data demonstrated that SlymiR208 is a positive regulator in leaf senescence through negatively regulating CK biosynthesis via targeting SlIPT2 and SlIPT4 in tomato. This study indicated that post-transcriptional regulation via miRNA is a control point of CK biosynthesis and added a new layer to the understanding of the regulation of CK biosynthesis in tomato and a new factual proof to support that miRNAs are involved in leaf senescence.
叶片衰老（leaf senescence）是植物生命周期中一个高度程序化的发育过程。细胞分裂素（cytokinin，CK）已被广泛认为是延迟叶片衰老的负调控因子。miRNA 通过负调控其靶基因的表达，在多种发育和生理过程中发挥关键作用。然而，迄今为止，miRNA 在 CK 生物合成中的作用尚不清楚，miRNA 对叶片衰老的调控知识仍然非常有限。异戊烯基转移酶（isopentenyltransferases，IPT）催化高等植物 CK 生物合成的初始和限速步骤。我们之前的工作表明，沉默番茄中的 SlIPT4 表达会导致叶片过早衰老。在这里，我们鉴定了一种新的番茄 miRNA，SlymiR208，它在转录后水平调节 SlIPT2 和 SlIPT4 的表达。SlymiR208 在番茄中广泛表达，其表达模式与衰老叶片中目标转录物相反。番茄中超表达 SlymiR208 可显著降低 SlIPT2 和 SlIPT4 的转录水平，以及叶片中内源 CK 的浓度。SlymiR208 过表达引起的早期叶片衰老与 SlIPT4 沉默系的表型一致。数据表明，SlymiR208 通过负调控 CK 生物合成，通过靶向番茄中的 SlIPT2 和 SlIPT4，是叶片衰老的正调控因子。本研究表明，miRNA 的转录后调控是 CK 生物合成的一个控制点，并为番茄中 CK 生物合成的调控提供了新的认识，并为 miRNA 参与叶片衰老提供了新的事实依据。
