The Function Of MED8 In Regulation Of The Juvenile-to-adult Phase Change In Arabidopsis

Vegetative phase chang is the premise for flowering in plants.It affects many important traits,including plant morphogenesis,yield,pest/disease resistance,abiotic stress response.Intiation of abaxial trichome on leaf blades and leaf shape are two key morphological markers to distinguish between juvenile and adult phases in Arabidopsis.Studies have shown that miR156 is the master regulator of the juvenile to adult phase change in plants.In our previous research,we identified mutants exhibiting delayed juvenile-to-adult-phase change phenotypes in an EMS-mutagenized SPL3pro::eGFP::SPL3-3'UTR M2 population.Map-based cloning showed that these two mutations encode one subunit of the Mediator complex,MED8.Here,we tried to study the genetic and molecular relationship between MED8 and miR156-SPL pathway by using these two med8 mutants.We hope to uncover the regulatory mechanism of MED8 in the juvenile-to-adult phase change in Arabidopsis with an aim to provide theoretical basis for targeted modification of plant growth by means of genetic engineering to achieve higher yieldand and better quality for crops.The main results of the study are as follows:(1)Phenotypic characterization of med8 and Col indicated that med8 has a prolonged juvenile phase than wild type in short days(SD)(2)qRT-PCR was employed to analyze the expression of genes in the miR156–SPL pathway in 9-,13-,17-day-old wild-type and med8-2 shoot apices.Pri-miR156 A and Pri-miR172 B,and miR172 were reduced in med8-2;whereas Pri-miR156 C was elevated in med8-2,and SPL9 remained no change in med8-2.(3)Genetic analysis indicated that Ubi10::mimicry156,Ubi10::rSPL3,pEG302::rSPL9 and toe1/toe2 rescued the prolonged juvenile phase of med8-2.(4)DEX induction and qRT-PCR experiment indicated that the transcript of Pri-miR172 B was induced in pSPL9::rSPL9::GR-3'UTR plants treated with DEX;whereas Pri-mi R172 B remained relatively constant in pSPL9::r SPL9::GR-3'UTR/med8-2 treated with DEX,implying that MED8 impairs SPL9 transcriptional activity.(5)MED8-BD baiter was constructed and used to screen the MED8 interactors by yeast two hybrid system.15 transcription factors showing interaction with MED8 were obtained.Overall,these results demonstrate that MED8 involves the juvenile-to-adult phase change in Arabidopsis through influencing the transcriptional activity of SPL9,thus affecting the expression of miR172.