Analysis of the Ethylene Response in theepinastic Mutant of Tomato

Abstract

Ethylene can alter plant morphology due to its effect on cell expansion. The most widely documented example of ethylene-mediated cell expansion is promotion of the "triple response" of seedlings grown in the dark in ethylene. Roots and hypocotyls become shorter and thickened compared with controls due to a reorientation of cell expansion, and curvature of the apical hook is more pronounced. The epinastic (epi) mutant of tomato (Lycopersicon esculentum) has a dark-grown seedling phenotype similar to the triple response even in the absence of ethylene. In addition, in adult plants both the leaves and the petioles display epinastic curvature and there is constitutive expression of an ethylene-inducible chitinase gene. However, petal senescence and abscission and fruit ripening are all normal in epi. A double mutant (epi/epi;Nr/Nr) homozygous for both the recessive epi and dominant ethylene-insensitive Never-ripe loci has the same dark-grown seedling and vegetative phenotypes as epi but possesses the senescence and ripening characteristics of Never-ripe. These data suggest that a subset of ethylene responses controlling vegetative growth and development may be constitutively activated in epi. In addition, the epi locus has been placed on the tomato RFLP map on the long arm of chromosome 4 and does not demonstrate linkage to reported tomato CTR1 homologs.

Reduced arbuscular mycorrhizal colonization in tomato ethylene mutants

“…Among the mutants tested, the intraradical colonization by G. clarum was significantly reduced in both ethylene mutants (epi and Nr) mostly when plants were grown under low P conditions. The epi mutant is constitutively activated in a subset of ethylene responses, including the expression of the ethylene-induced gene chi9, encoding a class I basic chitinase (Barry et al, 2001), whereas the Nr mutant is insensitive to ethylene (Wikinson et al, 1995). The reduction of AM formation in different ethylene contexts (low sensitivity and high production) is consistent with early suggestions that although this hormone is highly inhibitory for colonization (Azcón-Aguilar et al, 1981;Ishii et al, 1996;Geil et al, 2001), at low concentration it may also stimulate the fungal growth (Ishii et al, 1996).…”

“…The AM development in epi resembles that in reduced mycorrhizal colonization (rmc) tomato mutant, as described by Barker et al (1998). Since epi and rms are not allelic, as they map on chromosomes 4 (Barry et al, 2001) and 8 (Larkan et al, 2007), respectively, it would be interesting to investigate the relationship between these two mutants. Further studies are also necessary to determine whether the infection or the colonization process is inhibited in epi mutants.…”

“…Syn Solanum lycopersicum L.) mutants (Peres et al, 2005) with low sensitivity to auxin (diageotropica, Oh et al, 2006), cytokinin (bushy root, Pino-Nunes, 2005) and ethylene (Never ripe, Wikinson et al, 1995), as well as tomato mutants with high sensitivity to gibberellin (procera, Jones, 1987), low abscisic acid level (notabilis, Burbidge et al, 1999) and high ethylene production (epinastic, Barry et al, 2001) were obtained at the Tomato Genetic Research Center (University of California, Davis) and introgressed into the genetic model system cv Micro-Tom (MT), obtained at the Weizmann Institute of Science (Israel). The introgression of mutations into MT was performed as described previously (Lima et al, 2004).…”

“…As Arabidopsis, MT has a small size, short life cycle and amenability for genetic manipulation (mutant and transgenic plants production). Here, tomato mutants with low sensitivity to auxin (diageotropica, Oh et al, 2006), cytokinin (bushy root, Pino-Nunes, 2005) and ethylene (Never ripe, Wikinson et al, 1995), as well as tomato mutants with high sensitivity to gibberellin (procera, Jones, 1987), low abscisic acid level (notabilis, Burbidge et al, 1999) and high ethylene production (epinastic, Barry et al, 2001) into the MT background were used to study the formation of AM. Using this mutant collection we shown that epinastic and Never ripe, two ethylene-related mutations, have significant inhibitory effects on root colonization by Glomus clarum under low P conditions, when compared to MT controls, and that the effect of ethylene may be associated to the control of defense-relate responses.…”

Characteristics of fruit ripening in tomato mutant epi

“…Apart from epinasty, the epi phenotype is characterized by dark green leaves, thickened and shortened stems, apparent reduction in anthocyanin production, a shortened and highly branched root system, and a very erect and compact growth habit (Fujino et al, 1988;Wang and Ying, 2004 containing both epi and Nr (never ripe) genes, and found that the double mutant has the same dark-grown seedling and vegetative phenotypes as epi but possesses the senescence and characteristics of never ripening. No significant differences were observed between epi and VFN8 in many aspects, including the leaf and petal senescence or abscission, the rate of fruit ripening and the time from anthesis to the onset of fruit ripening (Barry et al, 2001).…”