Molecular Mechanism Of Root Meristem Development And De Novo Root Regeneration Regulated By MPK3/MPK6 Cascade In Arabidopsis

Mitogen-activated protein kinase(MAPK)cascades are ubiquitous signaling modules in eukaryotes.MAPK cascades are involved in almost every aspect of plant growth and development,including gametogenesis,embryogenesis,morphogenesis,senescence,abscission,fertilization,seed formation,and et al.Roots provide structural support to the aerial portion of plants,absorb water and nutrients that are crucial for plant growth and development.In this study,we investigated the role of MPK3/MPK6 cascade in regulating of root meristem development and de novo root regeneration.1.Regulation of root meristem development by MPK3/MPK6 cascade.In this study,we found that loss-of-function mutants of MPK3/MPK6 show a short-root phenotype,which is associated with reduced numbers of meristematic cells.Several key transcription factors are involved in the maintenance of RAM(Root Apical Meristem),including SHR-SCR,WOX5,and PLT1/PLT2.We found that conditional loss of MPK3/MPK6 led to a pronounced decrease in pro PLT1:PLT1-YFP and pro PLT2:PLT2-YFP expression,and meanwhile the intensities and patterns of the pro SHR:SHR-NLS-GFP and pro SCR:SCR-NLS-GFP reporters were not affected by the loss of MPK3/MPK6.In addition,the intensity of e CFP reporters driven by either the PLT1 or PLT2 promoter was also significantly reduced in the loss-of-function mpk3 mpk6 double mutant.Quantitative PCR(q PCR)results further supported that transcript levels of PLT1 and PLT2 in mutants were significantly lower compared to those in their controls.Taken together,our findings suggest that the MPK3/MPK6 functions upstream of PLT1/PLT2 pathway to modulate the stem cell population and primary root growth in Arabidopsis.2.Regulation of de novo root regeneration by MPK3/MPK6 cascade.Root organogenesis after damage is a type of plant regeneration known as de novo root regeneration(DNRR).We found that loss-of-function of MKK4/MKK5 or MPK3/MPK6 results in severely decreased adventitious rooting from leaf explants.In mkk4mkk5 and conditional mpk3 mpk6 double mutants,IAA failed to accumulate in the wound of the leaf explants.After exogenous supplement of IAA in the B5 medium,the adventitious rooting of mkk4 mkk5 and conditional mpk3 mpk6 double mutants could be partly but significantly recovered.q PCR results indicated that the transcript levels of YUC4,PIN1 and PIN3 in the mutants were significantly lower compared to that in the control plants.Taken together,we propose that MKK4/MKK5-MPK3/MPK6 cascade may regulate the DNRR process of Arabidopsis leaf explants by modulating the auxin accumulation at the wound during DNRR process.