GOLDEN 2: A Novel Transcriptional Regulator of Cellular Differentiation in the Maize Leaf

Abstract

The differentiation of distinct cell types within the leaf is essential for normal plant development. We characterized previously a transposon-induced mutant of maize ( bundle sheath defective1 ) that disrupts the differentiation of a single photosynthetic cell type in the leaf. In this study, we show that this mutation is allelic to golden2 ( g2 ), a lesion first reported 70 years ago. We cloned G2 by using Suppressor-mutator as a molecular tag. The gene encodes a 2.2-kb transcript that is present throughout the wild-type leaf but is most abundant in C 4 leaf blade tissue. Gene sequence data showed the existence of a bipartite nuclear localization signal encoded by the first exon, and we determined that G2 reporter gene fusions are targeted to the nucleus in onion epidermal cells. Further sequence analysis indicated the presence of a novel motif within the deduced protein sequence that shares features with TEA DNA binding domains. Therefore, we propose that G2 acts as a novel transcriptional regulator of cellular differentiation in the maize leaf.

Identification and cloning of GOLDEN2-LIKE1 (GLK1), a transcription factor associated with chloroplast development in Brassica napus L.

“…In the present study, no putative transmembrane domains were predicted in GLK1 proteins using the TMHMM program (Krogh et al, 2001), in accordance with the known properties of GLK1 proteins (Hall et al, 1998;Rossini et al, 2001). Based on the alignment results, the identity of the HLH domain was found to be 96.5%, showing high conservation among Brassicaceae species ( Figure 5 and Figure S3).…”

“…First, all GLK1 genes had remarkably conserved exon/intron structures (six exons/five intron) and intron phase patterns (0, 0, 0, 0, and 0), indicating that the GLK1 gene structure was established and retained following divergence of the Brassicaceae (Figure 4). Second, the amino acid sequence of the HLH domain was highly conserved, and the domain was composed of two helices, as reported for OsGLK1 and ZmGLK1 (Hall et al, 1998;Rossini et al, 2001). Alignment analysis revealed a higher level of conservation amongst GLK1 genes in Brassicaceae than in rice and maize ( Figure 5) (Rossini et al, 2001).…”

“…The present study showed that GLK1 in maize, rice, Arabidopsis, and P. patens is related to chloroplast development and regulation of plastid-encoded genes (Hall et al, 1998;Fitter et al, 2002;Waters et al, 2008Waters et al, , 2009Yasumura et al, 2005). In Arabidopsis, Chlorophyll accumulation was reduced in photosynthetic tissues following the loss of GLK activity, and was increased in non-foliar tissues by overexpression of GLKs (Waters et al, 2009).…”

“…Based on the alignment results, the identity of the HLH domain was found to be 96.5%, showing high conservation among Brassicaceae species ( Figure 5 and Figure S3). Furthermore, the putative helixloop-helix (HLH) DNA-binding domain in GLK gene families always consists of two helices that are separated by a 22-amino acid loop (Hall et al, 1998;Rossini et al, 2001), and Brassicaceae species contain a glutamic acid (E) residue within this 22-amino acid loop that is replaced with aspartic acid (D) in Arabidopsis species ( Figure 5). An aspartic acid (D) residue was found in OsGLK1 and ZmGLK1 (Rossini et al, 2001), suggesting that the sequences are highly conserved in related species.…”

“…In Arabidopsis, the pale green phenotype of the glk1 and glk2 double mutant is rescued by the transgenic expression of either of the two GLK genes (Waters et al, 2008(Waters et al, , 2009. ZmGLK1 is a homolog, and OsGLK1 is an ortholog, of GLK with similar phenotypes, which act as transcriptional regulators of cell type differentiation (Hall et al, 1998;Rossini et al, 2001). Although Chl accumulation in photosynthetic tissues was reduced in response to a loss of GLK activity, overexpression of GLK induced Chl accumulation and chloroplast biogenesis (Waters et al, 2009;Kobayashi et al, 2013;Wang et al, 2013).…”