Research & Laboratories

Research

a) The self-incompatibility fertilization system in Rosaceae (the main subject)

The Rosaceae botanical family contains several of the most important fruits, including apple, pear, peach, apricot, cherry and plum, all of which are cultivated in Upper Galilee in Israel. The Rosaceae are self-incompatible and, therefore, depend on cross-fertilization. Self-pollen is rejected because of the S-RNase-mediated gametophytic self-incompatibility (GSI) fertilization system. The GSI system is carried on a single locus (the S-locus). The S- locus harbors the S-RNase gene that governs the pistil-maternal part of the system, and the pollen-specific S-gene SLF/SFB that encodes an F-box protein. A pollen grain that lands on the stigma begins to germinate into the pistil, and the S-RNases which are present in the lumen of the pistil, enter the pollen tube by phagocytosis, regardless of its haplotype. It is suggested that mediation of SLF/SFB in the pollen grain leads to degradation of non-self S-RNase, whereas the self S-RNase is protected from degradation and is able to perform a cytotoxic function by digesting the RNA of the germinating pollen tube, and thereby inhibiting fertilization.

In our research we are studying the GSI mechanism in Rosaceae, and its impact on horticulture. We are investigating cases in which the GSI system does not function (i.e., in self-compatible cultivars) in order to learn about the system. In addition, we are conducting field experiments in Rosaceae orchards, in which we are monitoring pollination and fertilization.

We hypothesized that the reasons for the low fruit yield that is frequently observed in Israeli orchards could be the outcome of pollination and/or fertilization deficiencies. We have identified the S-RNase alleles of all the apple and pear, and of most of the plum and apricot cultivars grown in Israel. These alleles serve as genetic markers. Thus, the level of compatibility between cultivar couples and the pollen flow in these orchards can be determined. The field experiments that determine fruit set, seed set and yield are supported by molecular analysis of parents and progeny.

It has been found that semi-compatibility is a major reason for low yield in the sub-optimal climate conditions that prevail during the bloom in Israel, therefore, alternative, fully compatible cultivars have been planted. In addition the behaviour of bees on the flower and in the orchard is being monitored since a low extent of cross-pollination is a yield-limiting factor. As a result of these experiments new techniques of bee hive introduction are being applied which significantly improve the bee activity and efficiency of cross-pollination, leading to considerable increases in yield and fruit size.

b) Yeast as a biocontrol agent

We are studying yeasts as a biocontrol alternatives for fungicides. We are applying a molecular strategy in investigating the abilities that confer biocontrol competence. The biocontrol yeast Candida oleophila (Aspire ^TM) serves as the model system. A transformation system was developed and genes which are considered to be involved in biocontrol are over expressed or knocked out. This is the first time that this strategy has been applied to the study of a biocontrol yeast. Genes that are important for biocontrol are identified and provide the ability to improve existing agents by means of "self-modifications". In addition, we carry out an ongoing survey to identify and isolate new native yeasts with biocontrol abilities.

Recently we signed a research and development agreement with a multinational firm.

c) A molecular study of the ripening of climacteric fruit in respect to storage.

The stage at which fruit is picked and put into storage is a critical for long-term, high-quality preservation. However, the currently known parameters are not sufficient to serve as tools for the accurate identification of the best day for picking and for monitoring them during storage. The object of this research is to examine known genes and to identify new ones, which are involved in ripening, in order to develop them as markers and to broaden the understanding of the process. We track known genes such as ACC synthase, RS1, and β-galactosidase, and apply DNA chip technology in order to identify new genes. The experiments are performed in different storage conditions including the application of MCP1a chemical that reduces the ripening rate.