The maize MADS box gene ZmMADS3 affects node number and spikelet development and is co-expressed with ZmMADS1 during flower development, in egg cells, and early embryogenesis

MADS box genes represent a large gene family of transcription factors with essential functions during flower development and organ differentiation pro cesses in plants. Addressing the question of whether MADS box genes are inv olved in the regulation of the fertilization process and early embryo devel opment, we have isolated two novel MADS box cDNAs, ZmMADS1 and ZmMADS3, fro m cDNA libraries of maize (Zea mays) pollen and egg cells, respectively. Th e latter gene is allelic to ZAP1. Transcripts of both genes are detectable in egg cells and in in vivo zygotes of maize. ZmMADS1 is additionally expre ssed in synergids and in central and antipodal cells. During early somatic embryogenesis, ZmMADS1 expression is restricted to cells with the capacity to form somatic embryos, and to globular embryos at later stages. ZmMADS3 i s detectable only by more sensitive reverse transcriptase-PCR analyses, but is likewise expressed in embryogenic cultures. Both genes are not expresse d in nonembryogenic. suspension cultures and in isolated immature and matur e zygotic embryos. During flower development, ZmMADS1 and ZmMADS3 are co-ex pressed in all ear spikelet organ primordia at intermediate stages. Among v egetative tissues, ZmMADS3 is expressed in stem nodes and displays a gradie nt with highest expression in the uppermost node. Transgenic maize plants e ctopically expressing ZmMADS3 are reduced in height due to a reduced number of nodes. Reduction of seed set and male sterility were observed in the pl ants. The latter was due to absence of anthers. Putative functions of the g enes during reproductive and vegetative developmental processes are discuss ed.