ObjectiveThe auxinamide synthase gene family (GH3s) is a typical auxin primary/early response gene. Most family genes can regulate growth and development by regulating the concentration of free IAA in plants. Therefore, genetic engineering was used to introduce the BpGH3.5 sense and antisense strand into the Betula platyphylla genome in order to obtain fast-growing transgenic Betula platyphylla variety.

MethodIn total, 54 sense, antisense and control (WT) transgenic lines of BpGH3.5 were used in the study. Tree height, DBH and volume were measured. The genetic stability and relative expression of the target gene of five sense and antisense lines were detected by PCR and qRT-PCR, respectively. The free IAA content was determined by enzyme-linked immunosorbent assay.

ResultPCR showed that the nptII exogenous genes in the transgenic lines were all positive. qRT-PCR analysis showed that the BpGH3.5 gene was significantly higher in the five sense lines than in the WT line. In contrast, the endogenous BpGH3.5 was significantly down-regulated in the five antisense lines. The genome interfered the expression of BpGH3.5 in Betula platyphylla. The content of endogenous free IAA showed that the IAA content of the transgenic BpGH3.5 sense lines was significantly lower than that of the WT line. IAA content of the five antisense lines was significantly higher than that of the WT line (P< 0.01), and their average IAA content was 52.26% higher than the WT line. The differences in tree height, DBH and volume growth of 7-year-old transgenic BpGH3.5 Betula platyphylla were significant among lines (P< 0.01). Height, DBH and volume of transgenic lines were higher than the population mean, the antisense lines accounted for above 80%. In conclusion, transgenic BpGH3.5 antisense lines of Betula platyphylla can inhibit the expression of BpGH3.5, and reduce the ability of amino acid production resulting release more free IAA to promote the growth of Betula platyphylla. Ten fast growing trees were selected from antisense lines using principal component analysis. The average tree height, DBH and volume of these lines were 8.55%, 19.28%, and 50.42% higher than the population mean, respectively. The average genetic gain of tree volume was 36.3%. Results of selected lines provide useful information for future release transgenic BpGH3.5 lines in Betula platyphylla.

ConclusionTransgenic BpGH3.5 antisense lines of Betula platyphylla can inhibit the expression of BpGH3.5, and release more free IAA to promote the growth of Betula platyphylla. Ten fast growing trees were selected from antisense lines using principal component analysis.