Involvement of the MADS-Box GeneZMM4in Floral Induction and Inflorescence Development in Maize    

Abstract

The switch from vegetative to reproductive growth is marked by the termination of vegetative development and the adoption of floral identity by the shoot apical meristem (SAM). This process is called the floral transition. To elucidate the molecular determinants involved in this process, we performed genome-wide RNA expression profiling on maize (Zea mays) shoot apices at vegetative and early reproductive stages using massively parallel signature sequencing technology. Profiling revealed significant up-regulation of two maize MADS-box (ZMM) genes, ZMM4 and ZMM15, after the floral transition. ZMM4 and ZMM15 map to duplicated regions on chromosomes 1 and 5 and are linked to neighboring MADS-box genes ZMM24 and ZMM31, respectively. This gene order is syntenic with the vernalization1 locus responsible for floral induction in winter wheat (Triticum monococcum) and similar loci in other cereals. Analyses of temporal and spatial expression patterns indicated that the duplicated pairs ZMM4-ZMM24 and ZMM15-ZMM31 are coordinately activated after the floral transition in early developing inflorescences. More detailed analyses revealed ZMM4 expression initiates in leaf primordia of vegetative shoot apices and later increases within elongating meristems acquiring inflorescence identity. Expression analysis in late flowering mutants positioned all four genes downstream of the floral activators indeterminate1 (id1) and delayed flowering1 (dlf1). Overexpression of ZMM4 leads to early flowering in transgenic maize and suppresses the late flowering phenotype of both the id1 and dlf1 mutations. Our results suggest ZMM4 may play roles in both floral induction and inflorescence development.

The genetic architecture of leaf number and its genetic relationship to flowering time in maize

“…Upregulating and downregulating ZCN8 mRNA also causes changes in leaf number. Comparative genomics and mutant analyses have identified several other flowering time genes in maize (Sheehan et al ., 2007; Danilevskaya et al ., 2008; Miller et al ., 2008; Dong et al ., 2012). …”

Inflorescence Meristem Identity in Rice Is Specified by Overlapping Functions of Three AP1/FUL-Like MADS Box Genes and PAP2, a SEPALLATA MADS Box Gene

“…Generation of the PAP2 gene in grasses may be a molecular innovation in inflorescence development. Although the functions of PAP2 orthologs in other grass species remain to be analyzed, the maize (Zea mays) and wheat orthologs MADS4 and AGLG, respectively, exhibit expression patterns similar to that of PAP2, suggesting that their function may be conserved in grass species (Yan et al, 2003;Danilevskaya et al, 2008).…”

TheFT-LikeZCN8Gene Functions as a Floral Activator and Is Involved in Photoperiod Sensitivity in Maize

“…Transgenic plants overexpressing ZMM4 have an early-flowering phenotype. In addition, overexpression of ZMM4 in dlf1 or id1 mutants suppressed their late-flowering phenotypes, indicating ZMM4 likely functions downstream of id1 and dlf1 (Danilevskaya et al, 2008b). Rap2.7, an AP2-like transcription factor, is another flowering time gene and is thought to be a repressor of flowering time in maize (Salvi et al, 2007).…”

“…Homozygous mutants introgressed into the B73 inbred background were grown and tissues sampled as described previously (Danilevskaya et al, 2008b). The morphological development of the SAM of wild-type B73, dlf1, and id1 at different stages are shown in Figure 4A.…”

“…Transcript accumulation of ZMM4, a floral transition MADS box gene (Danilevskaya et al, 2008b), was assayed in shoot apices sampled from the same plants given the SD inductive photoperiod treatment ( Figures 2C and 2D). ZMM4 transcript was detected in shoot apices during and after the SD treatment.…”