Mitogen-activated protein kinase(MAPK)and leucine-rich repeat receptor-like kinase(LRR-RLK)signaling pathways have been shown to regulate diverse aspects of plant growth and development.In Arabidopsis,proper anther development relies on intercellular communication to coordinate cell proliferation and difierentiation.Two closely related genes encoding MAPKs, MPK3 and MpK6,function redundantly in regulating stomatal patteing.Although the mpk6 mutanthas reducedfertility,thefunction of MPK3 and MPK6 in antherdevelopmenthasnotbeen characterized.Similarly.the ERECTA(ER).ERECTA-LIKE1(ERLl)and ERL2 genes encoding LRR-RLKs function together to direct stomatal cell fate specification and the er-105 erll-2 erl2-1 triple mutant is sterile.Because the mpk3 mpk6 double null mutant is embryo Iethal,anther development was characterized in the viable mpl3/mpk6／-and er-105 erll-2 erl2-1 mutants.We found that both mutant anthers usually fail to form one or more of the four anther Iobes,with the er-105 erll-2 erl2-1 triple mutant exhibiting more severe phenotypes than those of the mpk3/mpk6／-mutant.The somatic cellIayers of the differentiated mutant Iobes appeared larger and more disorganized than that of wild-type.In addition.the er-105 erll-2 erl2-1 triple mutant has a reduced number of stamens,the majority of which possess completely undifferentiated or under-ditterentiated anthers.Furthermore, sometimes, the mpk3/+mpk6／-mutant anthers do not dehisce,and the er-105 erll-2 erl2-1 anthers were not observed to dehisce.Therefore,our resultsindicate that both ER/ERL1/ERL2 and MPK3/MPK6 play important roles in normal anther Iobe formation and anther cell differentiation.The close functional relationship between these genes in other developmental processes and the similarities in anther developmental phenotypes of the two types of mutants reported here further suggest the possibility that these genes might also function in the same pathway to regulate anther cell division and differentiation.