Temporal And Spatial Dynamic Changes Of The Lignin Content And The Expression Of Key Genes Of Brassica Napus Under Drought Stress

The edible vegetable oil of the world has 15% production per year come from Brassica napus, while 50% in our country. But such an important source of edible oil, the self-sufficiency rate is only 40% in our country. A series of factors, including drought and lodging, limited the rapeseed industry extension and development even though rapeseed is one of the major oil crops. In this study, first,5 B. napus lines were used to measure stem mechanical strength under drought stress and control. Second, we determined the lignin in root, stem and leaf at the different development stage, exploring the dynamic rules at the same time. On this basis, we last described the temporal and spatial expression patterns of lignin synthesis related genes. We expect that our results will provide some information and support for further exploring. Main results are as follows:We calculated the stem mechanical strength at stem elongation stage, early flowering stage, final flowering stage and the podding stage. The results showed that: the stem mechanical strength in drought stress gradually increased with development stage, but in control group the stem mechanical strength decreased at podding stage. The stem mechanical strength in drought group was higher than those in control group in all growth stage except stem elongation stage. The difference between the two groups was significant in final flowering stage and the podding stage. The genes, environment and growth stages affect stem mechanical strength.The lignin content grew and accumulated rapidly at early flowering stage and final flowering stage. While roots and leaves accumulated rapidly at the early flowering stage. Under our treatment, the lignin content varied with environments. Furthermore, at early flowering stage, final flowering stage and podding stage, the lignin accumulation under drought stress were faster than those under control group, but at the stem elongation stage, the lignin was not act as before. The lignin content significantly positive correlated with the stem mechanical strength, it meant the higher lignin content could help improve the stem mechanical strength.RNAs of root, stem and leaf tissue were extracted at every stage, respectively, followed by reverse transcription. The relative expression of six key genes at each stage was determined by real-time PCR. The results showed that the levels of transcription of PAL1、PAL2、4CL1 and CAD gene was elevated during early development and decreased at later stage. Interestingly, the expression level was higher under drought stress. Among these 4 genes, drought stress could delay the time at which PALI and CAD transcript reached the highest amount, with the peak occurring around final flowering stage. But both the drought treated group and control had the highest expression levels of PAL2 and 4CL1 at early flowering stage; C4H and CCoAOMT transcript was consistently increased during all stage, regardless of drought treated or not; reaching the peak transcriptional amount at podding stage.We calculated the correlation coefficients between the relative expression of the six genes and quantity of lignin, based on three different tissues of B. napus on two environmental conditions. The results indicated that 3 out of the 6 genes did not show significant correlation with lignin under control environment. In contrast, PAL1, PAL2 and 4CL1 had a positive effect on the bio-genesis of lignin, possibly in a synergy way. On the other hand, under drought stress, expression levels of C4H and CCoAOMT displayed a negative correlation to the level of lignin; however, PAL1 and 4CL1 showed a positive correlation. Besides, other than C4H and CCoAOMT, the rest genes act synergistically in the bio-genesis of lignin.In summary, lodging resistance in rapeseed is a very complex process, restricted and regulated by many factors. An appropriate drought treatment will be helpful to improve the rapeseed of the lignin content in the suitable time, the increase of the mechanical strength of stem and root will make rapeseed resist lodging.