Identification of WRKY transcription factor family and herbicide stress expression characteristics of the exotic weed Alternanthera philoxeroides

Alternanthera philoxeroides is an exotic weed with a wide invasion region and heavy invasion level in China, which has seriously harmed the balance of ecosystem services. WRKY is a type of plant specific transcription factor that plays an important role in herbicide stress response processes. To identify WRKY family members in A. philoxeroides, their characteristics were analyzed and the expression patterns were explored in response to herbicide stress. Consequently, 66 WRKY genes were identified in A. philoxeroides. These were divided into three subgroups (a, b, and c) according to their evolutionary relationships. The members in the same subgroup had similar gene structure, conservative motifs, and protein three-dimensional structure. Analysis of protein characteristics revealed that all ApWRKY proteins are hydrophilic. Expression patterns revealed that the expression of ApWRKYs was spatio-temporal specific. The herbicidal efficacy test showed that all five herbicides tested can decrease plant fresh weight and chlorophyll content. Among them, fluroxypyr exhibited the highest inhibition rate on fresh weight, whereas fluoroglycofen exhibited the highest inhibition rate on chlorophyll content. RT-qPCR analysis of herbicide response patterns of eight ApWRKYs showed that the expression level of two ApWRKYs increased first and then decreased after being induced by glyphosate, and the expression level of ApWRKY38.c was relatively stable within seven days after application. The expression levels of three ApWRKYs showed a decreasing trend after 0.5 to 3 days of treatment with isoproturon and fluoroglycofen. ApWRKY49.c and ApWRKY53.c were significantly induced to up-regulate their expression after 7 and 3 days of treatment with fluroxypyr and oxadiazon, respectively. These results indicate that ApWRKYs were involved in the response process of A. philoxeroides to herbicide stress and showed different spatio-temporal induction expression characteristics for different herbicides. This study lays the foundation for further exploration of the biological functions of ApWRKYs in response to herbicide stress.