HD2 overexpression induces dwarfism and elevated histone deacetylase activities in transgenic Ananas comosus variety MD2

Plant tissue culture has served as one of the most efficient biotechnological tools to mass produce high quality major crops. Nevertheless, the use of this technique can result in the occurrence of somaclonal variation, which may be brought upon by genetic and/or epigenetic modulations. The epigenetic modulation of plant growth, particularly on the importance of histone deacetylation/acetylation on genome stability, transcriptional regulation, as well as plant development, has been reported in several species such as Arabidopsis, rice, and maize. However, the information on its role in regulating the growth of major crops such as pineapple is still lacking. Previously, we had reported that supplementation of high cytokinin in the tissue culture media and exposure to salinity and abscisic acid (ABA) resulted in the production of somaclonal variants that exhibited dwarf phenotypes, and that these occurrences were associated with epigenetic modulation via the involvement of histone deacetylases (HDACs). Thus, in the present study, we aimed to further elucidate and verify the involvement of histone deacetylation in the occurrence of dwarfism in tissue culture-derived pineapple plants, through HD2 gene overexpression. AtHD2 gene from Arabidopsis thaliana was synthesized and expressed in phenotypically normal Ananas comosus. Transformation efficiency was also studied, and application of 200-µM acetosyringone was observed to be more efficient than 500 µM vanillin by 10%. The transgenic plants were observed to exhibit dwarfed phenotypes and showed significantly high HDAC enzyme activities. Ploidy evaluation of the transgenic plants showed no ploidy change had occurred in the samples and remained as 2n. The relative expression level of AtHD2 was also higher (3.2-fold up-regulation) in the transgenic plants compared to the wild type plants. Collectively, these results indicate that HDACs indeed played an essential role in the response of A. comosus towards abiotic stress, and that this phenomenon is epigenetically regulated.

Key words
pineapple; histone deacetylation; transgenic; transformation efficiency; dwarfism; abiotic stress