LeCTR1, a Tomato CTR1-Like Gene, Demonstrates Ethylene Signaling Ability in Arabidopsis and Novel Expression Patterns in Tomato

Abstract

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 CTR1, 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 ctr1-1 (constitutive triple response 1) mutant under the direction of the 35S promoter. Our data clearly show that ectopic expression of LeCTR1 in the Arabidopsis ctr1-1 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 ctr1-1 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.The plant hormone ethylene is involved in a variety of developmental and physiological processes in plants, including senescence, fruit ripening, and abscission (Abeles et al., 1992;Lelièvre et al., 1997;Giovannoni, 2001). It also plays an important role in physiological responses to environmental stresses such as water deficit, mechanical wounding, and pathogen attack (Abeles et al., 1992). The unraveling of the molecular basis of the ethylene perception and signal transduction pathway has been enhanced by the use of Arabidopsis mutants altered in the seedling triple response (Guzmàn and Ecker, 1990). The triple response is exhibited by seedlings treated with ethylene and results in: (a) inhibition of root elongation, (b) shortening and radial swelling of the hypocotyl, and (c) exaggerated curvature of the apical hook. Numerous loci have been identified and many corresponding genes cloned, representing various steps in ethylene signaling from receptors through transcription factors (Ecker, 1995;Johnson and Ecker, 1998;Stepanova and Ecker, 2000). The ETR1 gene was the first to be cloned (Chang et al., 1993) and was shown to encode a functionally active ethylene receptor (Schaller and Bleecker, 1995). Subsequently, it has been demonstrated that ETR1 belongs to a multigene family whose five members are differentially regulated (Schaller and Bleecker, 1995;Hua and Meyerowitz, 1998). Despite significant divergence at the structural and primary sequence level, all members of the ethylene receptor family are functionally active (Hua and Me...

Physical wounding and ethylene stimulated embryogenic stem cell proliferation and plantlet regeneration in protocorm-like bodies of Phalaenopsis orchids

“…The expression of CTR1, an ethylene receptor-signaling complex with ethylene receptor ETR1, and AtCTR1 was not affected by ethylene in Arabidopsis (Gao et al, 2003). However, CTR1 was previously found to be regulated by ethylene and its level increased during flower opening and fruit ripening in rose (RhCTR1 and RhCTR2) and tomato (LeCTR1) (Leclercq et al, 2002). Therefore, expression of PhCTR2 may be induced by ethylene (Figure 8).…”

Flower senescence: some molecular aspects

“…The expression analyses of these genes have also revealed their differential expression. Some of them have been reported to be expressed constitutively (LeCTR2, RhCTR2) while others (LeCTR1, RhCTR1) have been found to be upregulated during fruit ripening, flower opening, flower senescence and defense responses (Zegzouti et al 1999;Alexander and Grierson 2002;Leclercq et al 2002;Lin et al 2008;Hajizadeh et al 2011b). Similarly a homolog of CTR1 (Cup-CTR1) from Cucurbita pepo has been found to be upregulated in male flowers only (Manzano et al 2008).…”

Ethylene and fruit ripening: from illumination gas to the control of gene expression, more than a century of discoveries

“…However, as yet a number of these ER clones have no assigned function and reverse genetics is currently being used to investigate the function of these genes and address their role in the ripening process . The latest data have indicated that ER50 is a CTR-like clone, potentially involved in the ethylene transduction pathway (Leclercq et al, 2002;Adams-Phillips et al, 2004a) and ER24 is homologous to a multi-bridging factor involved in transcriptional activation while ER49 is a putative mitochondrial translation elongation factor that could be involved in the stimulation of mitochondrial activity by ethylene during the climacteric increase in respiration Benichou and Li et al, 2003). These genes are being extensively studied in order to determine their function and mechanisms of regulation by ethylene.…”

“…Later, several CTR1 homologous were isolated from tomato (Jones, 1999;Zegzouti et al, 1999;Leclercq et al, 2002;Adams-Phillips et al, 2004 a). The CTR1 product acts downstream of ETR1, ETR2, ERS1, ERS2 and EIN4 in the ethylene signal transduction pathway and corresponds to a negative regulator of other cascade components identified in Arabidopsis, including the ethylene-insensitive genes (EIN2 and EIN3) and the ethylene-response-factor (ERF1) (Giovannoni, 2004;Stepanova and Alonso, 2005).…”