Regulation of 2,4-D Isooctyl Ester on and Tillering and Endogenous Phytohormonal Responses.

Tillering is an important agronomic trait essential for the yield of and the propagation of . However, the effect of phytohormones on and tillering and the underlying regulatory mechanisms remain poorly understood. In the study, we found that and exhibited different tillering sensitivities to the auxin herbicide 2,4-D isooctyl ester. At 3 days post-application, tiller bud growth was inhibited by 77.50% in , corresponding to 2.0-fold greater inhibition than that in (38.71%). Transcriptome analysis showed that differentially expressed genes (DEGs) in the response to 2,4-D isooctyl ester were mainly enriched in plant hormone metabolism and signal transduction pathways, but similar changes were not observed in . Among that, the auxin biosynthesis and signaling induced by 2,4-D isooctyl ester was quite different between the two species. A total of nine candidate genes involved in varied tillering responses were selected from the DEGs and validated by quantitative real-time PCR. Endogenous hormone levels were assayed to further verify the RNA-seq results. After 2,4-D isooctyl ester treatment, a significant increase in abscisic acid (ABA) levels was observed in , whereas ABA levels were relatively stable in . The herbicide induced more cytokinin (CTK) accumulation in than in . External ABA clearly restricted tiller bud growth in both and , while 6-benzyl aminopurine had no significant effect. These results indicate that ABA and CTK may be related with 2,4-D isooctyl ester-regulated tillering differences between the two species, which will help to further understand the mechanism of the auxin-mediated regulation of tillering.