Mechanisms Of Callose Degradation In Arabidopsis Tetrads

After the meiosis stage,the pollen mother cell(PMCs)gradually transformed into the tetrad which contains four microspore covered by deposited callose.The callose will be degraded when the exine skeleton of pollen grains preliminarily formed in order to release the microspore.The absence of callose leads to abnormal exine,and results in male sterility.However,the mechanism of callos degaradation still unknown.AMS regulates MYB80 and TEK to control the formation of pollen exine in taptum,respectively.With the analyzing of relevant data,we found that these three transcription factors may participate in the degradation of tetrad callose by regualte the expression of five members of ?-1,3-Glucan family in taptum,which also known as A6 family.Then,in situ hybridization and subcellular localization indicated these A6.1,A6.2 and A6.3 were expressed in tapetum,and located in locule.The toluidine blue stain showed the quintuple mutants of a6.1/2/3/4/5 reslut in delayed degradation of callose.Meanwhile,the transmission electron microscope(TEM)reveal that the aberrant callose degration affect normal sexine developement in quintuple mutants.These suggest that A6.1?A6.2?A6.3?A6.4 and A6.5 are functional redundancy in callose degradation in anther.Furthermore,the biochemistry experiments such as Electrophoretic Mobility Shift Assays(EMSA)and transcriptional activation assay in tobaco indicated that those three transcription factors can co-activate A6.1 expression.These suggest the expession of A6 s requires these three factors.Therefore,the callose degradation is regulated by the developmental network of exine in terms of spatial and temporal activation,and the correct degradation process affect the development of the sexine.This work is the first time analyzed the genetic and molecular mechanisms of the process of callose degradation.It contributes to elucidate the regulation mechanism of callose degradation of tetrad and its affection to the anther development,and also provides new insight for the study about ?-1,3-glucanase in other plants.