Mechanisms Of Pollen Wall Development Pattern And Transcription Factor MS188 Regulating LAP5 / 6 Gene Involved In Pollen Outer Wall Synthesis

Plant sexual reproduction is not only a major approach of plant propagation, butalso one of the foundations for evolution and adaptation to the environment. Inangiosperm, the pollen wall plays an important role in protecting pollen from variousenvironmental stresses and bacterial attacks, promoting pollination and cell–cellrecognition between pollen and stigma. The pollen wall consists of two layers: theouter exine layer and the inner intine layer. The exine layer is divided into two layers:the sexine, and the nexine. Recently, a lot of genes in Arabidopsis are identified to beinvolved in pollen exine formation. The ablations of these genes lead to defectivepollen wall formation which is the reason for male-sterile phenotype. However, thedeposition model of pollen exine remains unclear. The first part of this paper focuson observing the formation and accumulation process of pollen exine in the antherdevelopment from stage6to9with transmission electron microscope. We clarifiedthat the accumulation of primexine is earlier than the tetrad stage and primexinemakes determination impact on the microspore plasma membrane. We inferred that,in tetrad, the periphery and inner cell wall of microspore may be not synchronizationand callose may also take part in the process of microspore plasma membraneformation. In addition, we observed some darker materials around the tetrad. Theymay be the precursory nexine of which elements may be different fromsporopollenin. When the microspores are released from the tetrad, these precursorswill assemble the pollen nexine. Based on the TEM observation, we present adevelopmental model of pollen exine formation in Arabidopsis.The MS188gene encodes an R2R3MYB family protein, which acts as a keytranscription factor for sexine formation. In ms188, mutated pollen grains werecompletely devoid of sexine while the nexine is still present. In order to elucidate theregulatory mechanism of MS188in pollen exine formation, we performed gene chipand global expression profiling analysis of wild-type and ms188mutant. We screenedtwo genes At4g34850(LAP5) and At1g02050(LAP6) related to Chalcone synthaseenzyme to investigate whether MS188dominated exine formation by regulating LAP5/6gene expression. Gene expression and RNA in situ hybridization reveal thatLAP5/6lay in MS188downstream. We constructed MS188genetic complementationwith GFP fluorescence protein and elucidated MS188combine the Lap5promoterbinding site with the experiments of ChIP and EMSA. We also constructedtransgenosis rescue plants (ProMS188::LAP5). Summary, the results indicated thatMS188, a key transcription factor of anther transcriptional, regulates LAP5expressionand takes part in pollen exine development directly. Investigation of thesemechanisms deepens our understanding of pollen development.