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A cold-regulated gene Lolium perenne LIR1 (LpLIR1) was isolated from perennial ryegrass using a subtractive approach. The gene has strong homology to the Light Induced Rice1 (LIR1) gene and is regulated at the transcriptional level by cold, and by a diurnal rhythm. Expression of LpLIR1 in perennial ryegrass was upregulated by vernalization but did not follow a standard vernalization-responsive expression pattern. LpLIR1 expression was restricted to vegetative tissues and absent in apices during floral induction and in flowers. LpLIR1 mRNA levels displayed diurnal fluctuations, which peaked before dusk and declined during the night. Heterologous expression of LpLIR1 in Arabidopsis led to a significant increase in leaf formation under short days (SD) conditions but only when plants had received a preceding vernalization treatment. Furthermore, dissection of plant development under SD revealed a minor but significant delay of flowering in the transgenic lines compared to wildtype plants. (c) 2006 Elsevier Ireland Ltd. All rights reserved.

A cold-regulated gene Lolium perenne LIR1 (LpLIR1) was isolated from perennial ryegrass using a subtractive approach. The gene has strong homology to the Light Induced Rice1 (LIR1) gene and is regulated at the transcriptional level by cold, and by a diurnal rhythm. Expression of LpLIR1 in perennial ryegrass was upregulated by vernalization but did not follow a standard vernalization-responsive expression pattern. LpLIR1 expression was restricted to vegetative tissues and absent in apices during floral induction and in flowers. LpLIR1 mRNA levels displayed diurnal fluctuations, which peaked before dusk and declined during the night. Heterologous expression of LpLIR1 in Arabidopsis led to a significant increase in leaf formation under short days (SD) conditions but only when plants had received a preceding vernalization treatment. Furthermore, dissection of plant development under SD revealed a minor but significant delay of flowering in the transgenic lines compared to wildtype plants. (c) 2006 Elsevier Ireland Ltd. All rights reserved.

Activation sequence-1 (as-1)-like regulatory cis elements mediate transcriptional activation in response to increased levels of plant signalling molecules auxin and salicylic acid (SA). Our earlier work has shown that tobacco cellular as-1-binding complex SARP (salicylic acid responsive protein) is primarily comprised of bZIP protein TGA2.2 and of minor amounts of a protein that cross-reacts with an antibody directed against related bZIP factor TGA2.1. As this protein was significantly smaller than recombinant TGA2.1, the origin of this protein had remained unresolved. Here we demonstrate that it corresponds to a distinct cleavage product of TGA2.1 generated during extract preparation. Overexpression of TGA2.1 led to increased levels of the TGA2.1/TGA2.2 heterodimer which was as effective with regard to enhancing the SA-inducibility of as-1 containing target gene Nt103 as corresponding amounts of the TGA2.2 homodimer. Thus, the TGA2.1 specific N-terminal domain, which had revealed transcriptional activation potential in yeast, did not show enhanced transcriptional activation in planta. TGA2.1 even had a negative effect on the SA-induced expression of the truncated CaMV 35S (-90) promoter that contains an isolated as-1-element upstream of the TATA-box. Plants expressing a TGA mutant deficient in DNA binding (TGA2.1trd) showed reduced levels of SA-inducible Nt103 expression, thus resembling plants expressing the analogous TGA2.2 derivative TGA2.2trd. In contrast to TGA2.2trd, TGA2.1trd did not reduce auxin-induced expression of Nt103 and SA-induced expression of pathogenesis related protein PR-1a, indicating that TGA2.1trd and TGA2.2trd differ in their capacity to outcompete regulatory factors involved in these regulatory pathways.