The Study Of Organogenesis Mechanism Of Pulvinus In Medicago Truncatula

Different with animals,plant cannot move.While the leaf of some species can move after sensing environmental stimulus,such as light,temperature,touch and chemicals.The phenomen on that legume leaf could move with the circadian rhythms called nyctinasty.Structurally,this type of movement mediated by a motor organ located in the basal of leaf and leaflet which called pulvinus.Leaf movement is caused by rhythmic expanding and shrink of motor cells of pulvinus,hence,pulvinus plays a vital role on leaf movement.Medicago truncatula is model plant of legume,and shows leaf movement.PLP(PETIOLULE-LIKE PULVINUS)specifically expressed in pulvinus.In loss-of-function of plp mutant,pulvinus alters to petiolule-like pulvinus,and has defect on leaf movement.PLP is homolog of Arabidopsis LOB(LATERAL ORGAN BOUNDARIES)which is involved in the formation of lateral organ boundary by repressing the accumulation of BR.However,application of BL(Brassinolide)in plp could not recover the petiolule-like pulvinus in plp,and application of PPZ(Propiconazole)in WT could not mimic the plp phenotype.Moreover,a Tntl retrotransposon tagged dawrf4 mutant was isolated in M.truncatula.DWARF4 is a member of P450 gene family,encodes a 22a hydroxylase whose reaction is a rate-limiting step in brassinosteroid biosynthetic pathway.BR level decreased in dwarf4.The petiolule-like pulvinus could not be recovered in dwarf4plp double mutant.These data suggested that BR content may not be responsible for the formation of pulvious.It is report that expression of DR5rev:GFP,a marker of auxin distribution,is higher in wild type than plp mutant.Analysis of RNA-seq showed that the expression levels of 24 auxin-related genes are down-regulated,and 8 auxin-related genes are up-regulated,implying that the auxin may be involved in pulvinus development.However,application of auxin and auxin inhibitor could not change the phenotype of pulvinus in WT and petiolule-like pulvinus in plp,suggesting that auxin play the limited roles in pulvinus development.YABBY genes mainly involved in lateral organ abaxial cell differentiation,loss-of-function of YABBY genes lead to polarity deficiency of lateral organ and ectopic lateral meristem.RNA-seq data showed that YABBYgenes are down-regulated in plp mutant,suggesting that pulvinus in WT is an abaxialized organ.Take together,BR and auxin may be involved in the formation of pulvinus.The change of polarity also plays the cricual roles in pulvinus development.