The Functional Study Of MtMAXs And MsPALM1 In Lateral Branch And Compound Leaf Development Of Medicago

Leaf morphology is an important part of plant morphogenesis.For most cultivated crops,leaf morphology and spatial distribution affect the light utilization efficiency and determine the yield and quality of crops to a large extent.In alfalfa,the leaf-stem ratio is one of the important factors related to the forage quality.The higher leaf-stem ratio of alfalfa,the greater biomass and utility it will become.Based on this point,molecular genetic improvement of alfalfa leaf pattern can provide theoretical basis and technical means for the cultivation of new alfalfa varieties with high quality and yield.The branching development of higher plants is a protective mechanism to avoid damage,adapt to the environment,and determine plant type.The morphogenesis of branching development and the morphologic changes of compound leaf development are closely related to biomass and yield.At present,increasing the number of branches and the complexity of compound leaves of alfalfa has become a very important task to improve the biomass and yield of forage.Medicago truncatula is the model legume species.The Tntl-tagged mutant population of M.truncatula has been applied in different research area in legume.This thesis includes two parts.In the first part,we found MtMAX3 and MtMAX4 are two genes related to strigolactone biosynthesis in M.truncatula.Further analysis showed that MtMAX3 encodes carotenoid cleavage dioxygenase CCD7 and MtMAX4 encodes carotenoid cleavage dioxygenase CCD8.We identified three M.truncatula Tntl-tagged mutant lines,mtmax3-1,mtmax4-1 and mtmax4-2,corresponding with the mutations of MtMAX3 and MtMAX4 respectively.Tissue specific expression analysis showed that the highest expression level was found in roots.All the three mutants showed increased lateral branch phenotypes,meanwhile,no obvious phenotypes were found in other organs of the mutant plants.The exogenous treatment with GR24(a synthetic analog of SLs)in mutants showed that lateral branch recovery of the mutants was positively correlated with GR24 concentration.GA3 exogenous treatment showed that the sensitivity response to GA was different between wild type and the mutants.Meanwhile,the lateral branch number and plant height in the wild-type and mutants treated with GA3 were similar to those of treatment with GR24,indicating that there might be a new crosstalk between SLs and GA signals.Compared with the wild type,the expression level of CKXs was significantly down-regulated in the mutants,suggesting that the deletion of the striglactone biosynthesis gene may affect the accumulation of CKs.The conserved function of the interaction between SLs and CKs in regulating lateral branch development in M.truncatula requires further investigation.In the second part of this paper,we constructed MsPALM1-RNAi vector and carried out the genetic transformation using wild-type alfalfa SY4D to study the effect of down-regulation of MsPALM1 expression on the numbers of alfalfa leaves.PALMATE-LIKE PENTAFOLIATAl(PALM1)encodes a Cys(2)His(2)zinc finger structural protein with unknown function and this gene is conserved among species.The experimental results showed that the leaves of transgenic plants showed palmate-shaped compound leaflet pattern and the late flowering phenotype.qRT-PCR results showed that the transcription level of endogenous MsPALM1 in transgenic plants was significantly down-regulated.For biomass index statistics,the total leaf area,the leaf-stem ratio and protein content of transgenic plants was significantly higher than those of wild type.