# Abscisic Acid--Defensive Player in Flax Response to _Fusarium culmorum_ Infection
## 3 Results
### Analysis of Transcript Levels of Genes Involved in Isoprenoid Biosynthesis
We analyzed twelve genes involved in the biosynthesis of carotenoids: phytoene synthase (\(PSY\)), phytoene desaturase (\(PDS\)), \(\zeta\)-carotene desaturase (\(ZCD\)), \(\zeta\)-carotene isomerase (\(Z\)-\(ISO\)), carotenoid isomerase (\(CRTSO\)), lycopene \(\beta\)-cyclase (\(LCYB\)), lycopene \(\varepsilon\)-cyclase (\(LCYE\)), \(\beta\)-carotene hydroxylase (\(\beta HY\)), \(\varepsilon\)-ring hydroxylase (\(LUTI\)), \(\beta\)-ring hydroxylase (\(LUTI\)), reaxanthin epoxidase (\(ZEP\)), violaxanthin de-epoxidase (\(VDE\)) at 6, 12, 24, 36 and 48 hpi. We observed an increase in the PSY gene transcript to 2.7- and 3.6-fold of the control at 24 hpi and 48 hpi, respectively. Although small in the beginning, an increase in the expression of Z-ISO gene was observed in each consecutive time-point reaching 3-fold of the control at 48 hpi. A similar expression profile was noted for CRTISO gene (with a maximum of 2.37- and 2.71-fold of the control at 36 hpi and 48 hpi, respectively. ZDS gene transcript level was increased at 12 hpi and 48 hpi to 1.55- and 1.76-fold of the control, respectively. Expressions of both lycopene cyclase genes (LCYB, LCYE) were decreased after the infection (only with 1.22-fold increase at 48 hpi, and 1.46-fold increase at 6 hpi,respectively). However, a considerable increase in the expression of \(\beta\)HY gene throughout all time-points was measured, reaching 3.65- and 3.88-fold of the control at 36 hpi and 48 hpi, respectively. Both ZEP and VDE gene expressions were slightly decreased in all time-points measured. LUT5 gene transcript level decreased till 36 hpi to increase at 48 hpi to 1.38-fold of the control, whereas the LUT1 gene expression changed over the time-points to reach its minimum at 36 hpi (0.46-fold of the control) and maximum at 48 hpi (1.46-fold of the control) (Figure 3D). Since further processing of carotenoids, connected with their degradation, leads to the production of other relevant compounds, such as strigolactones, volatile apocarotenoids and perhaps the most important to ABA, we analyzed the levels of expression of genes involved in this process: 9-cis-epoxycarotonoid dioxygenes (_NCED3, NCED6_), xanthoxin dehydrogenase (_ABA2_), abscisic aldehyde oxidase (_AAO3_), carotenoid cleavage dioxy  
Figure 3: Heatmap of terpenoid pathway key gene expression in flax after _F. culmorum_ infection (x—fold of the control). (**A**)—terpenoid backbone synthesis genes; (**B**)—bytosterol synthesis genes; (**C**)—tocopherol synthesis genes; (**D**)—carotonoid synthesis genes; (**E**)—apocarotonoid and ABA synthesis genes. Detailed results on the expression can be found in Supplementary File S3. genases (_CCD1_, _CCD7_, _CCD8_). We observed a substantial increase in the level of the _NCED3_ and _NCED6_ gene levels (up to 10.89- and 22.66-fold of the control, respectively at 36 hpi). Additionally, the level of _AAO3_ gene expression was elevated with its maximum of 3.79-fold of the control at 36 hpi, whereas the expression of _ABA2_ gene was decreased in all time-points (minimum of 0.63-fold of the control at 36 hpi). Expression levels of all three _CCD_ genes were down. In the case of _CCD1_, the decrease was relatively small, whereas for _CCD7_ and _CCD8_ the dropdown was considerable through all the time-points (to 0.28- and 0.53-fold of the control on average, respectively) (Figure 3E).