Chinese sprangletop (Leptochloa chinensis (L.) Nees) is a serious grass weed in rice paddies. In some areas, L. chinensis has become resistant to the herbicide cyhalofop-butyl because of its frequent and extensive use over the past five years. In this study, whole-plant dose-response assays were conducted, and a L. chinensis population (ZHYH) had a 75.8-fold resistance index to cyhalofop-butyl. Molecular analyses revealed that this resistance was attributed to a tryptophan (Trp)-2027-to-cysteine (Cys) substitution in the CT domain of the ACCase gene. To our knowledge, this is the first report revealing the mechanism underlying cyhalofop-butyl resistance in L. chinensis. Furthermore, a derived cleaved amplified polymorphic (dCAPS) assay was developed to rapidly detect the Trp-2027-Cys mutation. Of the 100 ZHYH plants analyzed, 52 were heterozygous mutants and 48 were susceptible homozygous plants. In addition, the cyhalofop-butyl-resistant L. chinensis was cross-resistant to aryloxyphenoxypropionate and phenylpyrazoline herbicides, but not to cyclohexanedione, acetolactate synthase-inhibiting, protoporphyrinogen oxidase, and urea herbicides, and had only slight resistance to the hormonal herbicide quinclorac.

APETALA3 (AP3) homologs are involved in specifying petal and stamen identities in core eudicot model organisms. In order to investigate the functional conservation of AP3 homologs between core eudicots and basal angiosperm, we isolated and identified two AP3 homologs from Magnolia wufengensis, a woody basal angiosperm belonging to the family Magnoliaceae. Sequence and phylogenetic analyses revealed that both genes are clade members of the paleoAP3 lineage. Moreover, a highly conserved motif of paleoAP3 is found in the C-terminal regions of MAwuAP3_1/2 proteins, but the PI-derived motif, usually present in AP3/DEF-like lineage members, is missing. Semi-quantitative and real time PCR analyses showed that the expression of MAwuAP3_1/2 was restricted to tepals and stamens. However, the MAwuAP3_1 expression was maintained at a high level during the rapid increased in size of tepals and stamens, while MAwuAP3_2 mRNA was only detected at the early stage of tepal and stamen development. Furthermore, the expression of MAwuAP3_1/2 in transgenic Arabidopsis causes phenotypic changes which partly resemble those caused by ectopic expressions of the endogenous AP3 gene. Moreover, the 35S::MAwuAP3_1/2 transgenic Arabidopsis can be used partially to rescue the loss-of-function ap3 mutant (ap3-3) of Arabidopsis. These findings call for a more comprehensive understanding of the B-functional evolution from basal angiosperm to core eudicot clades.