LATERAL ROOT PRIMORDIA 1 of maize acts as a transcriptional activator in auxin signalling downstream of the Aux/IAA gene rootless with undetectable meristem 1.

Only little is known about target genes of auxin signalling downstream of the Aux/IAA-ARF module. In the present study, it has been demonstrated that maize lateral root primordia 1 (lrp1) encodes a transcriptional activator that is directly regulated by the Aux/IAA protein ROOTLESS WITH UNDETECTABLE MERISTEM 1 (RUM1). Expression of lrp1 is confined to early root primordia and meristems and is auxin-inducible.

The Gibberellic Acid Stimulated-Like gene family in maize and its role in lateral root development.

In an approach to study lateral root development in monocots, genome-wide searches for homologs of the Gibberellic Acid Stimulated Transcript-like (GAST-like) gene family in rice (Oryza sativa) and maize (Zea mays) were carried out. Six novel GAST-like genes in rice and 10 members of the gene family in maize, which were designated ZmGSL (for Z. mays Gibberellic Acid Stimulated-Like), were identified.

The root cap determines ethylene-dependent growth and development in maize roots.

Besides providing protection against mechanical damage to the root tip, the root cap is involved in the perception and processing of diverse external and internal stimuli resulting in altered growth and development. The transduction of these stimuli includes hormonal signaling pathways such as those of auxin, ethylene and cytokinin. Here, we show that the root cap is essential for the ethylene-induced regulation of elongation growth and root hair formation in maize.

The maize (Zea mays L.) roothairless3 gene encodes a putative GPI-anchored, monocot-specific, COBRA-like protein that significantly affects grain yield.

The rth3 (roothairless 3) mutant is specifically affected in root hair elongation. We report here the cloning of the rth3 gene via a PCR-based strategy (amplification of insertion mutagenized sites) and demonstrate that it encodes a COBRA-like protein that displays all the structural features of a glycosylphosphatidylinositol anchor. Genes of the COBRA family are involved in various types of cell expansion and cell wall biosynthesis.

Conserved and diverse mechanisms in root development.

The molecular basis of root formation and growth is being analyzed in more and more detail in the dicot model organism Arabidopsis. However, considerable progress has also been made in the molecular and genetic dissection of root system development in the monocot species rice and maize. This review will highlight some recent molecular data that allow for the comparison of cereal and Arabidopsis root development.

WOX gene phylogeny in Poaceae: a comparative approach addressing leaf and embryo development.

The phylogeny based on the homeodomain (HD) amino acid sequence of the WOX (WUSCHEL-related homeobox gene family) was established in the 3 major radiations of the Poaceae family: Pooideae (Brachypodium distachyon), Bambusoideae (Oryza sativa), and Panicoideae (Zea mays). The genomes of all 3 grasses contain an ancient duplication in the WOX3 branch, and the cellular expression patterns in maize and rice indicate subfunctionalization of paralogues during leaf development, which may relate to the architecture of the grass leaf and the encircling of the stem. The use of maize WOX gene family members as molecular markers in maize embryo development for the first time allowed us to visualize cellular decisions in the maize proembryo, including specification of the shoot/root axis at an oblique angle to the apical-basal polarity of the zygote.

Transcription of the putative maize orthologue of the Arabidopsis DORNROSCHEN gene marks early asymmetry in the proembryo and during leaf initiation in the shoot apical meristem.

A potential orthologue of the Arabidopsis DORNROSCHEN (DRN) gene was isolated from maize based on phylogeny and expression patterns. ZmDRN transcription provides a new marker for embryonic patterning and cellular differentiation in the shoot apical meristem. In contrast to DRN expression in the 2-4-cell Arabidopsis embryo, transcription of the maize orthologue is activated only in the late proembryo stage where expression, however, marks the prospective scutellum domain such as DRN transcription prepatterns cotyledon development in the Arabidopsis globular embryo.

Pattern formation in the monocot embryo as revealed by NAM and CUC3 orthologues from Zea mays L.

All aerial parts of a higher plant originate from the shoot apical meristem (SAM), which is initiated during embryogenesis as a part of the basic body plan. In contrast to dicot species, the SAM in Zea mays is not established at an apico-central, but at a lateral position of the transition stage embryo. Genetic and molecular studies in dicots have revealed that members of the NAC gene family of plant-specific transcription factors such as NO APICAL MERISTEM (NAM) from Petunia or the CUP-SHAPED COTYLEDON (CUC) genes from Arabidopsis contribute essential functions to the establishment of the SAM and cotyledon separation.