LeCTR1, a tomato CTR1-like gene, demonstrates ethylene signaling ability in Arabidopsis and novel expression patterns in tomato

LeCTR1 was initially isolated by both differential display reverse transcriptase-polymerase chain reaction screening for tomato (Lycopersicon esculentum) fruit ethylene-inducible genes and through homology with the Arabidopsis CTR1 cDNA. LeCTR1 shares strong nucleotide sequence homology with Arabidopsis CTRL a gene acting downstream of the ethylene receptor and showing similarity to the Raf family of serine/threonine protein kinases. The length of the LeCTR1 transcribed region from ATG to stop codon (12,000 bp) is more than twice that of Arabidopsis CTR1 (4,700 bp). Structural analysis reveals perfect conservation of both the number and position of introns and exons in LeCTR1 and Arabidopsis CTR1. The introns in LeCTR1 are much longer, however. To address whether this structural conservation is indicative of functional conservation of the corresponding proteins, we expressed LeCTR1 in the Arabidopsis ctrl-1 (constitutive triple response 1) mutant under the direction of the 35S promoter. Our data clearly show that ectopic expression of LeCTR1 in the Arabidopsis ctrl-1 mutant can restore normal ethylene signaling. The recovery of normal ethylene sensitivity upon heterologous expression of LeCTR1 was also confirmed by restored glucose sensitivity absent in the Arabidopsis ctrl-1 mutant. Expression studies confirm ethylene responsiveness of LeCTR1 in various tissues, including ripening fruit, and may suggest the evolution of alternate regulatory mechanisms in tomato versus Arabidopsis.