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- Author or Editor: Carole L. Bassett x
- HortScience x
During the past several years, we have been interested in genes and gene-products involved in various aspects of ripening and maturation in peach (Prunus persica) fruit. The ethylene biosynthetic and signal transduction pathways are of particular interest due to the role of this hormone in such processes. Recently, we isolated a cDNA encoding a homologue of the ethylene receptor ETR1 from a near fully ripe (20–60N) peach fruit cDNA library. This cDNA clone, PpETR1, is nearly 2300 bp in length, with a 5' untranslated region of 268 bp, a 3' untranslated region of 150 bp, and an ORF of 1881 bp, encoding a protein of 70 kDa. The cDNA is most closely related to an ETR1 homologue from apple (Malus domestica), i.e., 95% identity at the amino acid level, but shows considerable similarity to Arabidopsis thaliana ETR1, as well. A comparison of the similarity among cloned ETR1 genes from a range of plant species will be presented.
Signal transduction plays a crucial role in an organism's response to its environment. Developmental processes like flowering in photoperiodically sensitive plants must employ some form of signal communication to effect this response. Protein kinases occupy an intermediate position in signal transduction pathways between signal perception and the final metabolic effect produced. Their importance is underscored by the fact that genes encoding protein kinases have been highly conserved during evolution. Over 30 independent clones were obtained by screening a genomic bank from morning glory DNA with a probe derived from a gene encoding a maize protein kinase. Selected clones were digested with SacI and the resulting DNA fragments transferred to filters for hybridization with the maize probe. The results indicate that these genes represent a small family comprised of approximately 5 members based on the hybridization conditions employed for their isolation.
NADP-dependent Malic Enzyme (NADP-ME, EC 1.1.1.40) catalyzes the decarboxylation of malate, resulting in the release of CO2. In C3 plants the enzyme does not contribute CO2 directly to photosynthesis. Rather, it is associated with the supplemental synthesis of glycolytic and Krebs Cycle intermediates, although it may also be involved in regulating intracellular pH. NADP-ME activity increases during ripening of several fruits e.g. tomato and apple, usually in association with increased respiration of the developing fruit. We examined expression of NADP-ME during ripening in peach using a cDNA probe derived from F. trinervia (C4 dicot). The probe hybridized to a single RNA species of the predicted size and was low in abundance as expected for a C3 NADP-ME. As fruit matured, the RNA levels increased to a maximum around 133-140 days after bloom (fully ripe). NADP-ME RNA was not detectable from leaves isolated at the same time.
Genes whose expression is regulated by exposure to low temperature (LT) in peach (Prunus persica L. Batsch.) bark were identified by PCR suppression subtractive hybridization. Among the genes identified by this technique were several that had previously been associated with LT responsiveness, as well as a few that have not been reported to be regulated by cold. Genes represented by the first group included Ppdhn1, previously characterized as a seasonally expressed gene predominantly seen in bark tissue collected in winter months. A novel dehydrin found in this study, Ppdhn3, was also observed to be up-regulated at LT and seasonally expressed. Two genes not previously associated with LT response were found to be up-regulated at 5 °C. These genes encode a polypeptide related to some unknown mitochondrial process (Pptar1p) or a transducin-like protein (Pptlp1) that may be associated with signal transduction. Expression of these genes with respect to seasonal variation and drought stress is compared to genes from peach bark (Ppdhn1 and Ppdhn2), whose patterns of expression in different seasons and under water deficit are well documented.
Reduced availability of water for agricultural use has been forecast for much of the planet as a result of global warming and greater urban demand for water in large metropolitan areas. Strategic improvement of water use efficiency (WUE) and drought tolerance in perennial crops, like fruit trees, could reduce water use without compromising yield or quality. We studied water use in apple trees using ‘Royal Gala’, a relatively water use-efficient cultivar, as a standard. To examine whether genes useful for improving WUE are represented in a wild relative genetically close to M. ×domestica, we surveyed Malus sieversii for traits associated with WUE and drought resistance using material collected from xeric sites in Kazakhstan. This collection has been maintained in Geneva, NY, and surveyed for various phenotypes and has been genetically characterized using simple sequence repeats (SSRs). These data suggest that most of the diversity in this population is contained within a subpopulation of 34 individuals. Analysis of this subpopulation for morphological traits traditionally associated with WUE or drought resistance, e.g., leaf size and stomata size and arrangement, indicated that these traits were not substantially different. These results imply that some of the genetic diversity may be associated with changes in the biochemistry, uptake, and/or transport of water, carbon, or oxygen that have allowed these trees to survive in water-limited environments. Furthermore, genes responding to drought treatment were isolated from ‘Royal Gala’ and categorized according to the biological processes with which they are associated. A large fraction of upregulated genes from roots were identified as stress-responsive, whereas genes from leaves were for the most part associated with photosynthesis. We plan to examine expression of these genes in the M. sieversii population during water deficit in future studies to compare their patterns of expression with ‘Royal Gala’.