Anne Frary

A member of the tomato Pto gene family confers sensitivity to fenthion resulting in rapid cell death.

Leaves of tomato cultivars that contain the Pto bacterial resistance locus develop small necrotic lesions within 24 hr after exposure to fenthion, an organophosphorous insecticide. Recently, the Pto gene was isolated and shown to be a putative serine/threonine protein kinase. Pto is one member of a multigene family that is clustered within a 400-kb region on chromosome 5. Here, we report that another member of this gene family, termed Fen, is responsible for the sensitivity to fenthion. Fen was isolated by map-based cloning using closely linked DNA markers to identify a yeast artificial chromosome clone that spanned the Pto region. After transformation with the Fen gene under control of the cauliflower mosaic virus (CaMV) 35S promoter, tomato plants that are normally insensitive to fenthion rapidly developed extensive necrotic lesions upon exposure to fenthion. Two related insecticides, fensulfothion and fenitrothion, also elicited necrotic lesions specifically on Fen-transformed plants. Transgenic tomato plants harboring integrated copies of the Pto gene under control of the CaMV 35S promoter displayed sensitivity to fenthion but to a lesser extent than did wild-type fenthion-sensitive plants. The Fen protein shares 80% identity (87% similarity) with Pto but does not confer resistance to Pseudomonas syringae pv tomato. These results suggest that Pto and Fen participate in the same signal transduction pathway.

An examination of factors affecting the efficiency of Agrobacterium-mediated transformation of tomato

An improved protocol for Agrobacterium-mediated transformation of the tomato cultivar Moneymaker was developed by examining the effects of six different factors on the efficiency of transformation. Explant size, explant orientation, gelling agent and plate sealant were found to affect transformation efficiency. Two other factors, type of explant (hypocotyl or cotyledon) and frequency of transfer to fresh selective regeneration medium, did not have any effect on transformation efficiency. By combining the best treatments for each factor, an average transformation efficiency of 10.6% was obtained for Moneymaker.

Salt tolerance in Solanum pennellii: antioxidant response and related QTL

BackgroundExcessive soil salinity is an important problem for agriculture, however, salt tolerance is a complex trait that is not easily bred into plants. Exposure of cultivated tomato to salt stress has been reported to result in increased antioxidant content and activity. Salt tolerance of the related wild species, Solanum pennellii, has also been associated with similar changes in antioxidants. In this work, S. lycopersicum M82, S. pennellii LA716 and a S. pennellii introgression line (IL) population were evaluated for growth and their levels of antioxidant activity (total water-soluble antioxidant activity), major antioxidant compounds (phenolic and flavonoid contents) and antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) under both control and salt stress (150 mM NaCl) conditions. These data were then used to identify quantitative trait loci (QTL) responsible for controlling the antioxidant parameters under both stress and nonstress conditions.ResultsUnder control conditions, cultivated tomato had higher levels of all antioxidants (except superoxide dismutase) than S. pennellii. However, under salt stress, the wild species showed greater induction of all antioxidants except peroxidase. The ILs showed diverse responses to salinity and proved very useful for the identification of QTL. Thus, 125 loci for antioxidant content under control and salt conditions were detected. Eleven of the total antioxidant activity and phenolic content QTL matched loci identified in an independent study using the same population, thereby reinforcing the validity of the loci. In addition, the growth responses of the ILs were evaluated to identify lines with favorable growth and antioxidant profiles.ConclusionsPlants have a complex antioxidant response when placed under salt stress. Some loci control antioxidant content under all conditions while others are responsible for antioxidant content only under saline or nonsaline conditions. The localization of QTL for these traits and the identification of lines with specific antioxidant and growth responses may be useful for breeding potentially salt tolerant tomato cultivars having higher antioxidant levels under nonstress and salt stress conditions.

Advanced backcross QTL analysis of a Lycopersicon esculentum × L. pennellii cross and identification of possible orthologs in the Solanaceae

In this study, the advanced backcross QTL (AB-QTL) mapping strategy was used to identify loci for yield, processing and fruit quality traits in a population derived from the interspecific cross Lycopersicon esculentum E6203 × Lycopersicon pennellii accession LA1657. A total of 175 BC2 plants were genotyped with 150 molecular markers and BC2F1 plots were grown and phenotyped for 25 traits in three locations in Israel and California, U.S.A. A total of 84 different QTLs were identified, 45% of which have been possibly identified in other wild-species-derived populations of tomato. Moreover, three fruit-weight/size and shape QTLs (fsz2b.1, fw3.1/fsz3.1 and fs8.1) appear to have putative orthologs in the related solanaceous species, pepper and eggplant. For the 23 traits for which allelic effects could be deemed as favorable or unfavorable, 26% of the identified loci had L. pennellii alleles that enhanced the performance of the elite parent. Alleles that could be targeted for further introgression into cultivated tomato were also identified.

QTL analysis of morphological traits in eggplant and implications for conservation of gene function during evolution of solanaceous species

Abstract. An interspecific F2 population from a cross between cultivated eggplant, Solanum melongena, and its wild relative, S. linnaeanum, was analyzed for quantitative trait loci (QTL) affecting leaf, flower, fruit and plant traits. A total of 58 plants were genotyped for 207 restriction fragment length polymorphism (RFLP) markers and phenotyped for 18 characters. One to eight loci were detected for each trait with a total of 63 QTL identified. Overall, 46% of the QTL had allelic effects that were the reverse of those predicted from the parental phenotypes. Wild alleles that were agronomically superior to the cultivated alleles were identified for 42% of the QTL identified for flowering time, flower and fruit number, fruit set, calyx size and fruit glossiness. Comparison of the map positions of eggplant loci with those for similar traits in tomato, potato and pepper revealed that 12 of the QTL have putative orthologs in at least one of these other species and that putative orthology was most often observed between eggplant and tomato. Traits showing potential orthology were: leaf length, shape and lobing; days to flowering; number of flowers per inflorescence; plant height and apex, leaf and stem hairiness. The functionally conserved loci included a major leaf lobing QTL (llob6.1) that is putatively orthologous to the potato leaf (c) and/or Petroselinum (Pts) mutants of tomato, two flowering time QTL (dtf1.1, dtf2.1) that also have putative counterparts in tomato and four QTL for trichomes that have potential orthologs in tomato and potato. These results support the mounting evidence of conservation of gene function during the evolution of eggplant and its relatives from their last common ancestor and indicate that this conservation was not limited to domestication traits.

Molecular mapping of the centromeres of tomato chromosomes 7 and 9.

The centromeres of two tomato chromosomes have been precisely localized on the molecular linkage map through dosage analysis of trisomic stocks. To map the centromeres of chromosomes 7 and 9, complementary telo-, secondary, and tertiary trisomic stocks were used to assign DNA markers to their respective chromosome arms and thus to localize the centromere at the junction of the short and long arms. It was found that both centromeres are situated within a cluster of cosegregating markers. In an attempt to order the markers within the centric clusters, genetic maps of the centromeric regions of chromosomes 7 and 9 were constructed from F2 populations of 1620Lycopersicon esculentum × L. pennellii (E × P) plants and 1640L. esculentum × L. pimpinellifolium (E × PM) plants. Despite the large number of plants analyzed, very few recombination events were detected in the centric regions, indicating a significant suppression of recombination at this region of the chromosome. The fact that recombination suppression is equally strong in crosses between closely related (E × PM) and remotely related (E × P) parents suggests that centromeric suppression is not due to DNA sequence mismatches but to some other mechanism. The greatest number of centromeric markers was resolved in theL. esculentum × L. pennellii F2 population. The centromere of chromosome 7 is surrounded by eight cosegregating markers: three on the short arm, five on the long arm. Similarly, the centric region of chromosome 9 contains ten cosegregating markers including one short arm marker and nine long arm markers. The localization of centromeres to precise intervals on the molecular linkage map represents the first step towards the characterization and ultimate isolation of tomato centromeres.

The genetic basis of seed-weight variation: tomato as a model system

Abstract The seeds of domesticated plants are normally much larger than those of their wild counterparts. This change in seed weight was most likely in response to the selection pressure for yield, uniform germination and seedling vigor which was exerted by humans during domestication. However, despite the evolutionary and agronomic significance of seed weight, very little is know about the genetic and developmental controls of this trait; and, thus far, none of the genes in this pathway have been isolated from any plant species. QTL mapping experiments conducted in tomato during the past decade have allowed the identification of many seed-weight QTLs and have also revealed that only a few loci are responsible for the majority of the seed-weight changes that accompanied the domestication of tomato. This review presents a consensus map for seed weight QTL identified in previously published reports and in unpublished results from our laboratory. This summary of seed-weight QTL data allows for the identification of the major loci controlling this trait in the genus Lycopersicon. It is hoped that this work will allow the elucidation of this important phenotypic transition that occurred during crop-plant domestication and will also provide the starting point for the cloning of a gene responsible for seed-weight variation.

Efficiency and stability of high molecular weight DNA transformation: an analysis in tomato

The efficiency of the binary bacterial artificial chromosome (BIBAC) vector for Agrobacterium-mediated stable transfer of high molecular weight DNA into plants was tested in tomato. Several variables affecting transformation efficiency were examined including insert size, Agrobacterium genetic background, and the presence of additional copies of the virG, virE1 and virE2 genes. It was found that a helper plasmid containing extra copies of virG was an absolute requirement for obtaining tomato transformants with the BIBAC. MOG101 with the virG helper plasmid was found to be the most efficient strain for transfer of high molecular weight DNA (150 kb). Selected high molecular weight DNA transformants were advanced several generations (up to the R4) to assess T-DNA stability. This analysis showed that the T-DNA was stably maintained and inherited through several meioses regardless of whether it was in the hemizygous or homozygous state. Expression of a selectable marker gene within the T-DNA was also examined through several generations and no gene silencing was observed. Thus, the BIBAC is a useful system for transfer of large DNA fragments into the plant genome.

An examination of factors affecting the efficiency ofAgrobacterium-mediated transformation of tomato

An improved protocol forAgrobacterium-mediated transformation of the tomato cultivar Moneymaker was developed by examining the effects of six different factors on the efficiency of transformation. Explant size, explant orientation, gelling agent and plate sealant were found to affect transformation efficiency. Two other factors, type of explant (hypocotyl or cotyledon) and frequency of transfer to fresh selective regeneration medium, did not have any effect on transformation efficiency. By combining the best treatments for each factor, an average transformation efficiency of 10.6% was obtained for Moneymaker.

Total antioxidant activity and total phenolic contents in different Turkish eggplant (Solanum melongena L.) cultivars.

In this study, total water soluble antioxidant activity and phenolic content of 26 eggplant ( Solanum melongena L. ) cultivars were investigated. Total water soluble antioxidant activity of the cultivars varied from 2664 to 8247 μmolTrolox/kg, which is a 3.1-fold difference. Cultivars also showed significant variation for total phenolic contents ranging from 615 to 1376 mg/kg, a 2.2-fold difference. The two traits were significantly correlated and results of this study suggested that breeders can use the information to develop eggplant cultivars with high antioxidant activity.