Potential Roles of Three ABCB Genes in Quinclorac Resistance Identified in Echinochloa crus-galli var. zelayensis

Echinochloa crus-galli var. zelayensis is a variant of E. crus-galli (L) Beauv, and it is the most pernicious weed in the east of China. Quinclorac, as synthetic auxin herbicide, could control this kind of weed effectively. In this study, two populations were used to further research the mechanism of quinclorac resistance, and the EcABCB1, EcABCB4 and EcABCB19 was functionally characterized to determine their roles in quinclorac resistance. It was found that root growth of quinclorac-resistant biotype SSXB-R was less inhibited by quinclorac at 5 mu M and 50 mu M when compared with the susceptible biotype JNNX-S. The results show that the IAA variations in root tip of JNNX-S were significantly higher than SSXB-R at 12 h after treatment with quinclorac (50 mu M) and 1-N-naphthylthalamic acid (100 mu M). There are no significant differences in IAA variations of the basal part of the root between susceptible and resistant biotypes after treatment with quinclorac and 1-N-naphthylthalamic acid (NPA). The transcript level of EcABCB1 and EcABCB19 in the root of JNNX-S showed down-regulated and up-regulated after treatment with quinclorac (TWQ) at 6 h in susceptible and resistant biotypes compared with control, respectively. The transcript level for EcABCB4 in the root showed up-regulated after TWQ at 12 h only in susceptible biotypes compared with control. It was found that the IC50 to quinclorac of AtABCB4 and AtABCB19 mutants were significantly higher than the parent line Col-0.