Position dependent expression of GL2‐type homeobox gene, Roc1: significance for protoderm differentiation and radial pattern formation in early rice embryogenesis

Abstract

SummaryIn early plant embryogenesis, the determination of cell fate in the protodermal cell layer is considered to be the earliest event in radial pattern formation. To elucidate the mechanisms of epidermal cell fate determination and radial pattern formation in early rice embryogenesis, we have isolated a GL2-type homeobox gene Roc1 (Rice outermost cell-speci®c gene1), which is speci®cally expressed in the protoderm (epidermis). In early rice embryogenesis, cell division occurs randomly and the morphologically distinct layer structure of the protoderm cannot be observed until the embryo reaches more than 100 mm in length. Nonetheless, in situ hybridization analyses revealed that speci®c expression of Roc1 in the outermost cells is established shortly after fertilization, much earlier than protoderm differentiation. In the regeneration process from callus, the Roc1 gene is also expressed in the outermost cells of callus in advance of tissue and organ differentiation, and occurs independently of whether the cells will differentiate into epidermis in the future or not. Furthermore, this cell-speci®c Roc1 expression could be induced¯exibly in the newly produced outermost cells when we cut the callus. These ®ndings suggest that the expression of Roc1 in the outermost cells may be dependent on the positional information of cells in the embryo or callus prior to the cell fate determination of the protoderm (epidermis). Furthermore, the Roc1 expression is downregulated in the inner cells of ligule, which have previously been determined as protodermal cells, also suggesting that the Roc1 expression is position dependent and that this position dependent Roc1 expression is important also in post-embryonic protoderm (epidermis) differentiation.

Isolation and characterization of two homeodomain leucine zipper genes from the dioecious plant Silene latifolia.

“…These results suggest that SlHDL1 functions in the early stages of the development of the epidermal tissues of anthers and gynoeciums and interacts with genes controlling the formation and function of floral organs. Similar expression patterns have also been reported for the homeodomain-GLABRA2 (HD-GL2) class, in which the homeodomain gene transcript can be detected in the outermost layers of maize (Ingram et al, 1999), rice organs (Ito et al, 2002;Yang et al, 2002), and the shoot apex of Arabidopsis (Lu et al, 1996), as well as for ATHB6, an HD-Zip gene the transcript of which was detected in the epidermis of the developing leaf of Arabidopsis (Soderman et al, 1999).…”

Genome-Wide Characterization of the HD-ZIP IV Transcription Factor Family in Maize: Preferential Expression in the Epidermis

“…In Arabidopsis, in situ hybridization and/or gene-specific promoter fusions to the GUS reporter gene revealed that nine of the 16 HD-ZIP IV genes show strongly enriched expression in the epidermis, whereas expression of one family member is limited to the subepidermal layer (Rerie et al, 1994;Lu et al, 1996;Masucci et al, 1996;Nakamura et al, 2006;Kubo et al, 2008). Similar results were obtained for all those genes characterized by in situ hybridization in rice (five genes) and maize (five genes; Ingram et al, 1999Ingram et al, , 2000Ito et al, 2002Ito et al, , 2003. Using laser microdissected outer and inner cell layers of juvenile leaves and of the SAM, we obtained layerspecific data for all ZmHDZIV genes but ZmHDZIV11 and ZmHDZIV12.…”

“…An exhaustive characterization of the 12 remaining Arabidopsis HD-ZIP IV genes by promoter::GUS fusions revealed that the promoters of HOMEODOMAIN GLABRA1 (HDG1), HDG2, HDG5, HDG7, HDG11, and HDG12 direct preferential expression in the epidermal layer of shoot organs (Nakamura et al, 2006). In rice, the five Rice outermost cell-specific genes for which detailed expression data are available are all specifically expressed in the epidermis (Ito et al, 2002(Ito et al, , 2003. Similarly, in maize, four of the five characterized Outer cell layer (OCL) genes (OCL1, OCL3, OCL4, and OCL5) are almost exclusively expressed in the epidermal layer, whereas OCL2 expression is restricted to the subepidermal layer of floral meristems (Ingram et al, 1999(Ingram et al, , 2000.…”

Transcription analysis of peloric mutants of Phalaenopsis orchids derived from tissue culture

“…One homoebox gene was recently cloned from the phalaenopsis inflorescence by using degenerate primers based on multiple nucleotide sequence alignment. The homeobox shows homology to the ovulespecific homeobox gene [51] and a rice GL2-type homeobox gene Roc1 specifically expressed in the protoderm or epidermal layer of rice embryo [52]. Stimuli of hormones, such as the auxin-regulated dual specificity cytosolic kinase may induce unusual cell division in the bulge regions of the peloric petals as shown in Fig.…”