Fungal Infection Affects Gene Expression in Transgenic Lemon Plants Producing an Antimicrobial Trichoderma harzianum Endochitinase

摘要

The development of disease-resistant genotype has been one of the top priorities in citrus genetic improvement programs. Several fungi diseases cause serious threat to lemon [ Citrus limon (L.)Burm. f. ] cultivation. Transgenic lemon clones with chit42 gene from Trichoderma harzianum have been obtained and showed increased resistance to some fungi. In the present work, the expression levels of several genes involved in biotic stress responses in chitA2 transgenic lemon clones upon Botrytis cinerea innoculation was investigated. Different resistancerelated processes, such as production of reactive oxygen species (ROS) , systemic acquired resistance (SAR) and induced systemic resistance (ISR) , were monitored in transgenic and wild type lemon clones. Expression of genes that encode gluthatione peroxidase (GPX) , a producer of ROS, chitinases, glucanases (SAR) , PAL, HPL, and AOS (ISR) was measured by quantitative RT-PCR during the first 24 hours after leaf inoculation. Leaves of transgenic lemon plants inoculated with B. cinerea showed significantly less lesion development and disease incidence than wild type leaves. Tissues from detached leaves of different transgenic lemon clones showed a significant correlation between resistance and transgene expression. On the other hand, the over-expression of the transgenic fungal gene enhanced by two-three folds transcript levels of genes associated with ROS production and ISR establishment, while the expression of native chitinase and glucanase genes involved in SAR was down-regulated.