Involvment Of The Populus Trichocarpa HDAC Gene Family In The Cold Stress Response

Histone deacetylases (HDACs) are a superfamily widely distributed in eukaryotes (including yeast, mammals and plants). HDACs act in concert with histone acetyltransferases (HATs) to regulate the status of histone acetylation, thus affecting the structure and function of the chromosome and regulating the gene transcription and a variety of functions of the cells.The researches on plant HDACs are gradually increasing, and many HDAC genes have been identified and characterized in different plants. Present studies have shown that HDACs are associated with plant development and stress responses. To date, the features and functions of HDACs from woody plants are poorly understood and relative studies have not been reported.This thesis analyzed the character of HDAC gene family in Populus trichocarpa and the expression patterns of HDAC genes under low temperature. Our results show that:1. Fifteen genes of HDAC family are mainly located in seven chromosomes of1,4,5,6,9,12and15, whilc only HDA912has not been determined yet. Physical and chemical property analyses show that most HDAC family members are hydrophilic proteins (HDA912belongs to hydrophobic protein), and the isoelectric point are acidic (except HDA912and SIR2subfamily). Cellular localization analysis predicts that HDAC family proteins are widely distributed in a cell, while they are mainly located in the nucleus, especially for HD2subfamily. HDACs are regulated by phosphorylation, and the phosphorylation sites mainly occur on serine residues. Only one site on tyrosine residue was found in HD2subfamily. Secondary structure analysis showes that the proportion of random coils of RPD3/HDA1subfamily (except HDA912) and SIR2subfamily members are more than50%, while the proportion of the a-helix of HD2subfamily members is zero and the random coils is80%. Phylogenetic analysis showed that HDAC family members in Populus trichocarpa can be divided into three subfamilies including RPD3/HDA1subfamily, HD2subfamily and SIR2subfamily, which is consistent with the classification of HDAC family in Arabidopsis and rice.2. HDAC family genes are all expressed in leaves, stems and roots, whereas different family members have different expression levels. Some genes (such as HDA902, HDA903HDT901and HDT902) have relatively high expression levels in roots, stems and leaves, while some genes (such as HDA901, HDA912, HDT903and SRT901) are mainly expressed in the leaves or stems, with relative low level in roots.3. The low temperature stress can affect the expression of the poplar HDAC genes. Most of populous HDAC genes are induced by low temperature, while only a small part of genes are not affected or are inhibited by low temperature. HDAC genes are significantly induced after long-term cold treatment for3days. The expression levels of HDA902, HDA903, HDA904, HDA908, HDA909, HDA912, HDT901, HDT902and HDT903are over2-fold upregulated. The expression of HDA901, HDA910and SRT901in stems or roots are slightly inhibited by low temperature. When the low-temperature stress was relieved, the expression of HDAC genes return to the pre-treatment level. In addition, HDAC specific inhibitor TSA can affect the expression of cold-related genes including CBF2. These results indicate that HDACs are probably involved in cold stress responses in Populus trichocarpa.