Control Of Organ Size By PUBX1 And PUBX2 In Arabidopsis Thaliana

The control of the size of plant organs is a basic developmental biology pro-cess,which is affected by complex genetic mechanisms and environmental fact ors.Studying organ size is an important frontier and research hotspot in plant developmental biology.There are significant differences in organ size between different species of plants,while the final organ size is remarkably uniform wit-hin a given species,indicating that the growth of a plant organ to its final size is tightly regulated by internal genetic factors.Plant organ growth is compo-sed of two main processes: cell division and cell expansion.In this study,we studied the function of PUBX1,an important growth regulator in the model p-lant species Arabidopsis and its homologous gene PUBX2 by combinations of plant molecular biology,cell biology and biochemistry approaches.PUBX1 and PUBX2 encode U-box E3 ligases that potentially function in the ubiquitin-med-iated protein degradation pathways.We characterized the length,width,surface area and diameter of the petals and leaves of wild-type,pubx1,pubx2 singlemonos mutants and the pubx1 pubx2 double mutant.Statistic analysis showed no significant difference between wild-type and both single mutants,while the PUBX1 PUBX2 double mutant appeared to have significantly enlarged organs when compared with wild-type.The results indicated PUBX1 and PUBX2 funct-ion redundantly to regulate organ development in Arabidopsis.Furthermore,we constructed transgenic plants overexpressing PUBX1 and PUBX2 genes by Gateway techniques.The expression level of PUB gene was n-egatively correlated with the organ size.The higher expression of PUB genes results in more reduced organ size in the plant.We also constructed transgenic plants overexpressing mutated PUBX1 and PUBX2 without the U-box domain(? PUBX1 and ? PUBX2)and the transgenic plants look similar to WT,which indicate that the U-box domain is required for the function of the PUBX1 and PUBX2 genes.In order to further understand the expression pattern of PUBX1 and PUBX2,we constructed transgenic plants expressing the GUS marker gene fused with the PUBX1 PUBX2 promoter,or the PUBX1 PUBX2 full-length protein.Histoc h-emical staining analysis of transgenic plants showed that PUBX1 and PUBX2 were expressed at higher levels in fully-open flowers,and much lower at you n-ger stages.We also did kinematic analysis of petal growth in the pubx1 pub x-2 double mutant and wild type.The results suggested that PUBX1 and PUB X2 genes regulated the duration of cell division thus affecting the organ develo p-ment.Our studies on molecular mechanism of plant growth and development pro-vide a theoretical basis for plant genetic improvement.The mechanism of plant organ size regulation will help to improve crop yield and solve the food crisi-s with far-reaching practical significance.