Identification and characterization of SmPIC30, an important gene that controls resistance to the auxin herbicide picloram in eggplant

Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) is a synthetic auxin herbicide that often disrupts the growth and development of dicotyledonous plants. Arabidopsis PIC30 (AtPIC30) is a specific target that mediates sensitivity to picloram, but a putative orthologue of AtPIC30 in eggplant (Solanum melongena L.) has not been characterized. In this study, we identified PIC30 genes in eggplant. Analyses of the phylogenetic relationships, gene structures, conserved domains and motifs revealed the evolutionary conservation of PIC30 among eggplant, tomato, pepper and Arabidopsis. Subcellular localization analysis indicated that SmPIC30 was a plasma membrane-localized protein. Tissue-specific expression analysis revealed that SmPIC30 was expressed in flowers, leaves and fruits, with the highest expression in flowers. Interestingly, the expression of SmPIC30 was significantly upregulated by picloram treatment. Virus-induced gene silencing (VIGS) assays indicated that knocking down SmPIC30 enhanced resistance to picloram, furthermore, the transcriptions of the auxin coreceptor encoding gene SmAFB5 was increased and the transcription of the auxin response genes SmIAA19 and SmIAA29 decreased in SmPIC30-knockdown plants. The hypocotyl elongation of the 35S::SmPIC30 transgenic lines (OE) in Arabidopsis were significantly longer than those of non-transgenic plants (Col-0) under normal condition, but the hypocotyl elongation in OE was sensitive to picloram treatment compared to those of Col-0. The present study suggests that SmPIC30 plays an important role in the response to picloram.