Improved tolerance toward fungal diseases in transgenic Cavendish banana (Musa spp. AAA group) cv. Grand Nain.

The most devastating disease currently threatening to destroy the banana industry worldwide is undoubtedly Sigatoka Leaf spot disease caused by Mycosphaerella fijiensis. In this study, we developed a transformation system for banana and expressed the endochitinase gene ThEn-42 from Trichoderma harzianum together with the grape stilbene synthase (StSy) gene in transgenic banana plants under the control of the 35S promoter and the inducible PR-10 promoter, respectively. The superoxide dismutase gene Cu,Zn-SOD from tomato, under control of the ubiquitin promoter, was added to this cassette to improve scavenging of free radicals generated during fungal attack. A 4-year field trial demonstrated several transgenic banana lines with improved tolerance to Sigatoka. As the genes conferring Sigatoka tolerance may have a wide range of anti-fungal activities we also inoculated the regenerated banana plants with Botrytis cinerea. The best transgenic lines exhibiting Sigatoka tolerance were also found to have tolerance to B. cinerea in laboratory assays.

The ubiquitin extension protein S27a is differentially expressed in developing flower organs of Thompson seedless versus Thompson seeded grape isogenic clones.

In Vitis vinifera L. cv. Thompson Seedless, fertilization occurs but seeds abort, a type of stenospermocarpy. To clone transcripts with differential expression during flower development, suppressive subtractive hybridization was carried out using two isogenic clones 'Thompson seedless' and 'Thompson seeded', at three stages of inflorescence development (from bud break to ~20 days prior to anthesis). Differential screening and sequencing of a forward and reverse subtractive cDNA library yielded several singleton ESTs. One differentially expressed clone in 'Thompson' seeded versus seedless isogenic clones was the ubiquitin extension protein S27a. In situ hybridization demonstrated its significantly higher expression in the carpel and ovaries of 'Thompson' seedless versus seeded isogenic clones during flower development. Overexpression of this gene resulted in abnormal plant regeneration and inhibited shoot development compared to controls; its silencing in embryogenic callus induced cell necrosis and callus death, evidencing tight regulation of this gene in developing organs of grape. S27a overexpression in carpels and integuments of the seedless flower may interfere with normal development of these organs, leading to embryo abortion and seedlessness.

Suppression and overexpression of ubiquitin extension protein S27a affects cell proliferation and in vitro regeneration in Nicotiana benthamiana.

Ubiquitin is a highly conserved 76-amino-acid protein found in all eukaryotic cells. Ubiquitin's expression is encoded and expressed as multimeric head-to-tail repeats (polyubiquitins) that are post-translationally cleaved into monomers, or fused with ribosomal proteins S27a and L40. S27a is highly expressed in meristematic tissues, pollen and ovules and its ubiquitin moiety is thought to act as a chaperone in ribosome biogenesis prior to cleavage. This study suggests that the ribosomal protein S27a plays a critical role in the allocation of meristematic cells that differentiate into lateral structures such as leaves and flowers. S27a was also found to regulate floral meristem development, possibly through the control of cell proliferation as well as cell identity. Overexpression of S27a was correlated with increased proliferation of undifferentiated cells and arrest of morphologically "normal" shoot and leaf development. The ubiquitin moiety did not affect the localization of S27a, but it did affect its protein level: expression of S27a without the ubiquitin moiety caused a severe reduction in S27a protein level.

Silencing of chaperonin 21, that was differentially expressed in inflorescence of seedless and seeded grapes, promoted seed abortion in tobacco and tomato fruits.

Vitis vinifera L. cv. 'Thompson Seedless' presents a type of stenospermocarpy in grape where fertilization occurs but seeds abort and fail to develop. To unravel the molecular basis for stenospermocarpy in grapes, subtractive hybridization was carried out in order to isolate differentially regulated genes that participate in the seedlessness machinery. Two 'Thompson' lines, a seeded and a seedless, were screened during different flower developmental stages. One of the genes, that was differentially expressed between the seeded and seedless lines, was the chloroplast chaperonin 21 (ch-Cpn21). ch-Cpn21 is a 21-kDa co-chaperonin polypeptide formed by two GroES-like domains fused together in tandem. Silencing of ch-Cpn21 in Nicotiana benthamiana plants resulted in leaf stunting, chlorosis, as well as ovary necrogenesis leading to seed abortion. Moreover, organ-specific silencing of ch-Cpn21 only in Lycopersicum esculentum fruits resulted in the development of seedless tomatoes. These results suggest that ch-Cpn21 may play a role in seed abortion in stenospermocarpic grapes.