Tomato plants transgenic for an Arabidopsis thaliana cystein proteinase inhibitor (Atcys) impair the life cycle of Helicoverpa armigera (Hüb.)

Atcys tomato (Lycopersicon esculentum Mill.) transgenic plants, expressing a cystein proteinase inhibition level double than the untransformed control (Speranza et al. in press), were used for in vivo assays with H. armigera larvae. This insect pest, extremely polyphagous, has recently caused severe damages to the outdoor tomato crop due to the dropping of infested young fruits and to fruit rotting because of the larval galleries. Plants of the cv. Riogrande (RIG) and of the corresponding Atcys homozygous transgenic line (BG-106) were grown in greenhouse and leaves utilized for feeding H. armigera larvae, reared for four days with artificial diet. The recorded data were larval weight (every two days until the cocoon stage), cocoon sex and morphometric traits, number of adults emerged from the cocoon, number of layed and hatched eggs. The mean weight was generally higher when larvae were fed with BG-106 leaves. By subdividing in three periods the larval life, no difference in mortality was observed between larvae reared with control (RIG) and with BG-106 leaves. The percentage of adults emerged from the cocoon was 81% and 76% for the control and BG-106 respectively. The sex ratio (males/females) was in favour of the female sex both for the RIG (0.87) and BG-106 (0.73) cocoons. On average, the fertility (number of layed eggs) of the BG-106 fed females was 33% lower than the control. By considering the percentage of hatched eggs (emerged larvae), the value obtained was 6.8% for BG-106 against 11% for RIG. According to these data, in Atcys transgenic tomato (BG-106), a level of cystein proteinase inhibition double than the untransformed control, is sufficient to negatively influence the H. armigera biological cycle, even if the weight of the larvae fed with the BG-106 leaves is on average higher than the control (RIG). The last datum is in agreement with similar experiments reported in literature where the effect of proteinase inhibitors is tested in different host-pest systems

Genetic and molecular mechanisms underlying the parthenocarpic fruit mutation in tomato

Parthenocarpy allows fruit set independently of fertilization. In parthenocarpic-prone tomato genotypes, fruit set can be achieved under pollen-limiting environmental conditions and in sterile mutants. Parthenocarpy is also regarded as a quality-related trait, when seedlessness is associated with positive fruit quality aspects. Among the different sources of genetic parthenocarpy described in tomato, the parthenocarpic fruit (pat) mutation is of particular interest because of its strong expressivity, high fruit set, and enhanced fruit quality. The complexity of the pat “syndrome” associates a strong competence for parthenocarpy with a complex floral phenotype involving stamen and ovule developmental aberrations. To understand the genetic basis of the phenotype, we mapped the pat locus within a 0.19-cM window of Chr3, comprising nine coding loci. A non-tolerated missense mutation found in the 14th exon of Solyc03g120910, the tomato ortholog of the Arabidopsis HD-Zip III transcription factor HB15 (SlHB15), cosegregated with the pat phenotype. The role of SlHB15 in tomato reproductive development was supported by its expression in developing ovules. The link between pat and SlHB15 was validated by complementation and knock out experiments by co-suppression and CRISPR/Cas9 approaches. Comparing the phenotypes of pat and those of Arabidopsis HB15 mutants, we argued that the gene plays similar functions in species with fleshy and dry fruits, supporting a conserved mechanism of fruit set regulation in plants