Mechanism Analysis of Increased Erucic Acid Content in Brassica napus L. Seeds Resulting Low Nighttime Temperature

Brassica napus L. (B. napus L.), a crop of Brassica in the family Cruciferae, is a major sources of edible vegetable oil and one of the four most widely grown. Oil accumulation is determined by genetic and environmental factors, including temperature, light, humidity, edatope, latitude, and altitude. Temperature also plays a crucial part in the maturation stage. A highly temperature-sensitive line (STSL, DH0729DH0815) and weakly temperature-sensitive line (WTSL, DH0729) were used to express LOC106368911 and its effect on the erucic acid content of seeds under low nighttime temperatures. Condition of 20/18 °C (±0.5 °C, daytime/nighttime temperature, CK) and 20/13 °C (low nighttime temperature, LNT) were used in tests. Under LNT, the erucic acid content in STSL seeds increased significantly, whereas the WTSL change was not significant. The relative expression of LOC106368911 was significantly increased in STSL at 27, 35 and 43 days after flowering (DAF), whereas the change in WTSL was not significant. The CDS sequence of the LOC106368911 was cloned. Compared to the protein sequence encoded by the reference gene, STSL changed the 96th amino acid sequence from I (leucine) to L (isoleucine). However, there was no difference in the secondary and tertiary structures. Based on this, we cloned the LOC106368911 promoter sequence and found that the mutation of C to T at position -790 in WTSL caused the loss of LTR (cis-acting element involved in low-temperature responsiveness, -791 to -786) element function in response to low temperature and increased erucic acid content. The LOC106368911 promoter had 2 LTR elements in STSL (-791 to -786 and -588 to -583). A GUS reporter vector was constructed to study the transient expression in tobacco leaf transformations. GUS gene expression at 13 ℃ after 2 h was significantly higher than that at 18 ℃. Base and number differences in the LTR element were found in the LOC106368911 promoter sequence of STSL and WTSL. Base mutations occurred in the LTR element in WTSL, which resulted in decrease or loss of erucic acid content in response to low nighttime temperatures.