Study of genetic modifications of flower development and methylation status in phytoplasma infected Brassica (Brassica rapa L.)

Abstract

Background: The plants of B. rapa (syn. B. campestris) are the most important food crop of Pakistan for the production of cooking oil. Brassica plants infected by phytoplasma exhibit floral abnormalities including phyllody, virescence, hypertrophied sepal and aborted reproductive organs and affected flower developmental genes which reduces the yield manifold.

Methods and results: The expression level of flower developmental genes in healthy and phytoplasma infected brassica were compared by using semi-quantitative reverse transcription polymerase chain reaction and DNA hybridization. In infected brassica, LEAFY (LFY) gene, controlling the development and maintenance of floral organ, and directly involved in controlling the homeotic gene expression was affected, while APETALA2, regulate the production of sepals and petals, were not altered. Whereas the genes WUSCHEL, APETALA3 and AGAMOUS, were significantly down-regulated, that were responsible for the identity of shoot and central meristem, petals and stamens production, and stamens and carpels development, respectively. The GLUB gene, controlling the production of β-1,3-glucanases enzyme, was highly up-regulated. According to DNA hybridization results, AGAMOUS and APETALA3 were restricted to floral organs territories in healthy and phytoplasma infected brassica, indicating that their expression was tissue-specific. These outcomes indicated that flower abnormalities of phytoplasma infected B. rapa are linked with DNA methylation in the expression of homeotic genes regulating flower development.

Conclusions: Azacitidine act as a DNA demethylating reagent. By applying the foliar spray of azacitidine during the flower development, cells of Phytoplasma infected plants exhibits demethylation of DNA when treated with azacitidine chemical that incorporated as analogue of cytosine during the cell division stage. B. rapa showed the up-regulation of gene expression level significantly that restore the normal production of flowers, ultimately increase the oil production throughout the world.

Keywords: Azacitidine; DNA methylation; Homeotic gene; Hybridization; Phenotype; Phytoplasma.