## 3 Results
### Expression Levels of PAs Metabolism Genes and lovB in A. terreus WT and HY Strains  
In order to explain the reasons of increased resistance of the high-yielding LOV producer to ODC inhibitors, we studied the expression levels of the most important PAs biosynthesis genes, such as _odc_, _samdc_ (encodes S-adenosylmethionine decarboxylase, AdoMetDC; EC 4.1.1.50) and _spds_ (encodes spermidine synthase, SpdS; EC 2.5.1.16). We also determined the expression level of the _oz_ gene (encodes the antizyme of ornithine decarboxylase, OAZ), a negative regulator of ODC lifespan in the fungi cell. To determine the biosynthetic status of the strains with regard to LOV production during cultivation on CDA medium, the expression levels of _lovA_ (encodes cytochrome P450, dihydromonacolin L monooxygenase LovA; EC 1.14.14.124), _lovB_ (encodes lovastatin nonaketide synthase LovB; EC 2.3.1.161), _lovC_ (encodes trans-acting enoyl reductase LovC; EC 2.3.1.161), _lovD_ (encodes 2-methylbutyl/monacolin J transesterase LovD; EC 2.3.1.238), _lovE_ (encodes GAL4-like transcription factor, LOV pathway-specific positive regulator LovE), _lovF_ (encodes lovastatin diketide synthase LovF; EC 2.3.1.244), and _lovG_ (encodes thioesterase LovG; EC 2.3.1.244) were also measured.. LovB is the so-called central enzyme of LOV biosynthesis, catalyzes the first 35 consecutive reactions for the polymerization and modification of 9 molecules of manoyl-CoA with the formation of dihydromonacalin L [29]. It turned out that during the cultivation on solid synthetic medium (CDA) in _A. terreus_ HY strain _lovB_ is upregulated, about 10-fold (Figure 3). Previously, we demonstrated that, under conditions of deep fermentation on the defined media, _lovB_ is upregulated 30-35-fold as compared to _A. terreus_ WT [11]. It is known that at different nutrient media the expression of _lov_ genes in _A. terreus_ can be regulated differently [30; 31]. Thereby detection of _lovB_ upregulation during the cultivation of _A. terreus_ HY under not optimal (for LOV biosynthesis) conditions is rather important. We also found the upregulation of other studied _lov_ genes in _A. terreus_ HY strain on CDA medium. _lovA_ was upregulated about 20-fold, _lovC_ was upregulated about 1.5-fold, _lovD_ was upregulated 10-15-fold, _lovE_ was upregulated 7-9-fold, _lovF_ was upregulated 5-6-fold, and _lovG_ was upregulated about 6-8-fold (Figure 3). The upregulation of these _lov_ genes on CDA medium was, as in the case of _lovB_, weaker compared to previously shown the increase in mRNA expression during the fermentation on the defined media, where _lovA_ was upregulated more than 150-fold, _lovC_ was upregulated 2-3-fold, _lovD_ was upregulated 20-30-fold, _lovE_ was upregulated 10-15-fold, _lovF_ was upregulated 12-18-fold, and _lovG_ was upregulated about 10-15-fold [11].  
From the results obtained, it is seen that in the context of _lovB_ upregulation, the _A. terreus_ HY strain has also an increased expression of genes for key enzymes of PAs biosynthesis (Figure 3). In LOV high-yielding strain _odc_ is upregulated, by 3-3.5-fold, _samdc_ is upregulated, by 7-10-fold, _spds_ is upregulated, by 3-4-fold (Figures 3 and 4). On the contrary, _oz_ is downregulated, by 4-6-fold (Figures 3 and 4). The combined effect of upregulation of _odc_ and, at the same time, downregulation of _ozz_, can lead to an additional increase in the content of ODC in _A. terreus_ HY cells (Figure 4). This can lead to increased resistance of the HY strain to ODC inhibitors. After 15 days, the addition of 5 mM APA inhibits the WT strain by 100%, the HY strain inhibits by 62%; the addition of 5 mM DFMO inhibits the WT strain by 49% and inhibits the HY strain by 25% (Figures 2 and 4).  
Figure 3: Relative gene expression in _A. terreus_ WT and HY strains: _lowA_ (**a**), _lowB_ (**b**), _lovC_ (**c**), _lovD_ (**d**), _lovE_ (**e**), _lovE_ (**f**), _lovG_ (**g**), _odc_ (**h**), _oza_ (**i**), _samdc_ (**j**), and _spds_ (**k**), 15 days after inoculation on CDA medium. Data are means \(\pm\) SD, \(n=3\).