EXORDIUM– a gene expressed in proliferating cells and with a role in meristem function, identified by promoter trapping in Arabidopsis

Abstract

To identify new genes expressed in meristematic cells, a promoter trap insertional mutagenesis strategy was used in Arabidopsis thaliana. Transgenic line AtEM201 exhibits promoter trap GUS activity in embryos and in the regions of active cell division in the seedling, notably the apical meristems and young leaves. The tagged gene was named EXORDIUM (EXO). AtEM201 contains a single copy of the promoter trap T-DNA, located in the EXO gene promoter, resulting in a much reduced level of EXO transcription. Seedlings homozygous for the T-DNA insertion have no obvious mutant phenotype. The EXO gene, which forms part of a small gene family in Arabidopsis, is structurally related to the tobacco PHI-1 gene, which is re-activated in cultured cells following release from phosphate starvation-induced cell cycle arrest. Expression of both the EXO-GUS and the native EXO genes is downregulated by exogenous cytokinin. Expression studies using semisynchronised cells suggest that EXO mRNA is preferentially abundant during M phase of the cell cycle. Double mutant studies revealed that the exo mutation can suppress the defective root meristem phenotype of the hydra2 mutant, suggesting that EXO may be a component of a negative regulatory system for cell division.

Transcriptomic Events Involved in Melon Mature-Fruit Abscission Comprise the Sequential Induction of Cell-Wall Degrading Genes Coupled to a Stimulation of Endo and Exocytosis

“…This extracellular EXO gene was identified as a potential mediator of BR-promoted growth [36], and it is part of a gene family with eight members in arabidopsis. As EXO is presumably involved in a signaling process which coordinates BR-responses with environmental or developmental signals, it cannot be ruled out that EXO protein might be involved in cell enlargement associated with the early induction of melon MFA.…”

Two Subclasses of Differentially Expressed TPS1 Genes and Biochemically Active TPS1 Proteins May Contribute to Sugar Signalling in Kiwifruit Actinidia chinensis

“…2 showed homology to EXORDIUM ( EXO ), which has a role in meristem function in Arabidopsis [65], cell expansion and brassinosteroid (BR)-mediated responses [66] and growth during low carbon and energy-limiting conditions [67]. More recently, it was demonstrated that apoplastic EXO protein modifies intracellular sucrose and trehalose responses and thus connects the extracellular C status to growth [68]; trehalose feeding induced Arabidopsis EXO expression, and therefore a potential increase in trehalose synthesis after AcTPS1 .…”

Transcriptomic analysis of juvenile wood formation during the growing season in Pinus canariensis

“…EXORDIUM (EXO) is another relevant gene found in this work, previously described in proliferating cells (Farrar et al 2003). First, it was suggested to be a negative regulator of cell division control and meristem maintenance.…”