Overexpression of Brassica rapa NGATHA1 Gene Confers De-Etiolation Phenotype and Cytokinin Resistance on Arabidopsis thaliana

Abstract

Brassica rapa NGATHA1 (BrNGA1) encodes a B3-type transcription factor. By analyzing Arabidopsis overexpressors of BrNGA1 (BrNGA1ox), we have previously demonstrated that BrNGA1 may be involved in negative regulation of cell proliferation during lateral organ and root growth. In the present study, we have found that BrNGA1ox seedlings grown in the dark display de-etiolation phenotypes, such as short hypocotyls, open and elongated cotyledons, and developing true leaves. BrNGA1ox seedlings as well as adult plants and calli are also resistant specifically to exogenous cytokinins. These data raise the possibility that the de-etiolation phenotypes of BrNGA1ox seedlings may result from an alteration in cytokinin response. We set out to test whether the de-etiolation phenotype is due to cytokinin overproduction or constitutively activated cytokinin response. First, BrNGA1ox was crossed to the CKX2ox plant, an overexpression line of CYTOKIN OXIDASE 2, which is responsible for degradation of active cytokinins. We found, however, no difference in the de-etiolation and shoot growth phenotypes between BrNGA1ox and BrNGA1ox CKX2ox plants. Next, we measured the transcripts level of ARR5 and ARR7, frequently employed as molecular markers for cytokinin signaling and yet found no difference in their transcripts levels of the wild-type and BrNGA1ox seedlings and shoots. These data indicate that biological role of BrNGA1 involved in de-etiolation seems to be associated with neither cytokinin overproduction nor its altered signaling. Possible molecular mechanisms by which BrNGA1 may interfere with cytokinin responses and etiolation are discussed.

Dynamic Expression of Imprinted Genes Associates with Maternally Controlled Nutrient Allocation during Maize Endosperm Development

“…Among the 11 MEGs, an APETALA2/B3-like transcription factor gene (GRMZM2G423393) ( Figure 2D) is highly similar to NGATHA1 (NGA1) in Arabidopsis, which redundantly together with three other NGA genes (NGA2 to NGA4) direct style development in the gynoecium through the YUCCA (YUC)-mediated auxin synthesis pathway (Alvarez et al, 2009). Additionally, overexpression of the Brassica rapa gene Br-NGA1 in Arabidopsis reduces lateral organ growth by inhibiting cell proliferation (Kwon et al, 2011). Of the 19 PEGs, 14 were paternally expressed as early as 3 DAP, and most (13 of 14) of their imprinted expression persisted until 15 DAP ( Figure 2D).…”

Expression of a NGATHA1 Gene from Medicago truncatula Delays Flowering Time and Enhances Stress Tolerance

“…NGA1 specifically binds the 5 -CACCTG-3 DNA sequence [4], and NGA family have been shown to be involved in the development of flower organs and leaves, cell proliferation in lateral organs, and seed development. BrNGA1 has been suggested to be involved in negatively regulating cell proliferation during lateral organ and root growth, and BrNGA1 transgenic seedlings displayed de-etiolation phenotypes under dark conditions [14]. NGAs and CINCINNATA-class-thermoresponsive cationic copolymers (CIN-TCPs) are co-expressed at many stages of leaf development, and their absence causes persistent marginal growth in leaves, cotyledons and floral organs [15].…”

Transcriptomic Analysis of Leaf Sheath Maturation in Maize

“…Transcription factors may also play important roles in distinguishing sheath tissues from blade tissues. The B3 domain-containing transcription factor NGA1 , which negatively regulates cell proliferation in Brassica rapa [37,38], is expressed at a high level in the sheath ( GRMZM2G082227 ) tissue only, which may suggest its role in prohibiting the development of sheath tissue into blade tissue. The maize NTT ( NO TRANSMITTING TRACT ) homologs GRMZM2G071101 and GRMZM2G445684 , two members of the C2H2-type zinc finger family that determine the distal cell fate in the root and influence transmitting tract development and pollen tube growth in Arabidopsis [39,40,41], as well as the homeobox family member GRMZM2G034113 , the homolog of which (the AtHB7 gene) is involved in ABA signaling during water stress, were all highly expressed in the sheath tissue and exhibited quite low expression in the blade [42,43].…”