Oilseed rape MPK1 mediates reactive oxygen species-dependent cell death and jasmonic acid-induced leaf senescence

Abstract

Leaf senescence is the terminal phase of leaf development, which involves remobilization of nutrients from leaves to other organs and is affected by many different endogenous (e.g. hormonal) and external stimuli. A proper control of leaf senescence is essential for fitness of annual plants. Although great progress has been made in identifying key genes or proteins controlling leaf senescence in Arabidopsis and several other plants, the relevant genes controlling leaf senescence in oilseed rape ( Brassica napus ) remain largely elusive. In this study, we found that a Mitogen-activated Protein Kinase, BnaMPK1 from oilseed rape positively modulated reactive oxygen species (ROS) -dependent cell death and jasmonic acid (JA)-induced leaf senescence. The expression of BnaMPK1 dramatically increased in senescing leaves of oilseed rape. Transient expression of BnaMPK1 in Nicotiana benthamiana and rapeseed protoplasts resulted in accumulation of ROS and cell death. Moreover, ectopic expression of BnaMPK1 in Arabidopsis exhibited accelerated JA-induced leaf senescence while atmpk1 mutants showed delayed leaf senescence. Furthermore, the expression of chlorophyll degradation and senescence marker genes Non-Yellowing 1 ( NYE1 , SGR1 ), Non-Yellow Coloring 1 ( NYC1 ), Senescence-Associated Gene 29 ( SAG29 ) and two well-known gene mediating JA-induced senescence ORESARA ( ORE ) 1 and ORE9 were induced in BnaMPK1 overexpression lines, whereas most of them were repressed in the atmpk1 mutant. A bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assay revealed that BnaMKK3 interacted with BnaMPK1 and, constitutively active BnaMKK3 phosphorylated BnaMPK1 whereas inactive BnaMKK3 can not. Taken together, these results indicate that BnaMPK1 acts as a positive regulator of ROS- and JA-dependent leaf senescence. • BnaMPK1 expression level is up-regulated in senescing leaves. • BnaMPK1 expression induces ROS-dependent cell death in leaves and protoplasts of oilseed rape. • BnaMPK1 modulates jasmonic acid (JA)-induced leaf senescence. • BnaMPK1 expression induces the transcription of a few senescence-associated marker genes. • BnaMPK1 interacts with upstream BnaMKK3 and is phosphorylated by BnaMKK3.