ZmHox: a novel class of maize homeobox genes

Abstract

Clones of two highly related genes, ZmHox2a and ZmHox2b (Zea mays homeobox), were isolated from maize embryo cDNA libraries by screening with the ZmHox1a homeobox sequence. The genes map to chromosomes 3 and 8, respectively, and encode mRNA transcripts of 6kb. The encoded proteins, ZmHox2a and b, share 84% sequence identity and exhibit a modular structure with several novel plant-specific protein domains. Interestingly, each ZmHox2a, gene product contains two complete homeodomains which, for Zmhox2a, were both shown to be functional DNA-binding motifs in vitro. Not only probes encoding the homeobox but also DNA fragments corresponding to other ZmHox2 domains hybridize to multiple bands in genomic Southern blots, indicating that related protein domains may be conserved in other maize genes. The ZmHox2a/b genes, therefore, are members of a novel and large class of maize genes, some of which can be expected to encode new transcription factors.

Transcriptional activation by the PHD finger is inhibited through an adjacent leucine zipper that binds 14-3-3 proteins

“…ZMHOX gene products have been shown to enter the plant cell nucleus (18) and bind to DNA (1,19), suggesting that these DNA-binding proteins regulate transcription. Unfortunately, loss of function mutations in plant PHDf-HD genes are neither available for the ZMHOX genes (ZMHOX1a/b and ZMHOX2a/b) (20) nor the Arabidopsis HAT3.1 (2) or PRHA gene or PRHP, its relative from Petroselinum crispum (21). The main function of PHDf-HD genes in plants therefore remains to be established.…”

Radial axis differentiation in a globular embryo is marked by HAZ1, a PHD-finger homeobox gene of rice

“…It has a PHD-finger domain at a central portion and a homeodomain at a C-terminal portion, both of which are characteristic of the members of the PHD-finger family homeodomain proteins. There are putative nuclear localization signal repeats in an N-terminal portion and acidic regions between the PHD-finger domain and the homeodomain, both of which also exist in Zmhox1a/b and Zmhox2a/b (Klinge et al, 1996;Uberlacker et al, 1996). These overall structural features are very similar to Zmhox1 proteins (Fig.…”

“…Overexpression of Zmhox1a or Zmhox1b in tobacco caused several abnormalities such as dwarfism, a loss of apical dominance and homeotic changes of flower organs . Zmhox1a was also shown to localize in a nucleus and bind a specific DNA sequence (Bellmann and Werr, 1992;Klinge et al, 1996;Comelli et al, 1999). From these results Zmhox1 genes are thought to function in certain developmental processes in maize by controlling expression of target genes.…”

“…Some proteins of this family have two homeodomains together with the PHD-finger domain (Klinge et al, 1996). Zmhox genes of maize, members of this family, were mainly expressed in meristematic cells (Klinge and Werr, 1995).…”

Dosage regulation of Zea mays homeobox (ZmHox) genes and their relationship with the dosage-sensitive regulatory factors of Shrunken 1 (Sh1) in maize

“…The experiments also address the possibility of whether the dosage effects could be mediated by the homeobox regulators. ZmHox1a and 2b were mapped to the long arm of chromosome 8 [Bellmann and Werr, 1992], ZmHox1b to 6L, and ZmHox2a to 3L [Bellmann and Werr, 1992;Klinge et al, 1996;Uberlacker et al, 1996]. The feasibility of constructing dosage series for 8L and 6L and the cloning of ZmHox1a and 1b allowed us to examine further the relationship of the dosage sensitive modifiers of Sh1 with the regulatory factors thought to be involved in its expression.…”