| Summary: | Auxin, the first discovered phytohormone, is important for the growth and development of plants through the establishment of homeostasis and asymmetry. Here, we cloned the auxin transporter gene <i>PIN-FORMED3</i> (<i>PIN3</i>) from the valuable timber tree hybrid <i>Liriodendron</i> (<i>Liriodendron chinense</i> × <i>Liriodendron tulipifera</i>). The gene contained a complete open reading frame of 1917 bp that encoded 638 amino acids. Phylogenetic analysis indicated that LhPIN3 exhibited the highest sequence similarity to the PIN3 of <i>Vitis vinifera</i>. Quantitative real-time PCR analysis showed that <i>LhPIN3</i> was broadly expressed across different tissues/organs of <i>Liriodendron</i>, with the highest expression level in the roots. Heterologous overexpression of <i>LhPIN3</i> in <i>Arabidopsis thaliana</i> caused considerable phenotypic changes, such as the root length and number of flowers. Genetic complementation of <i>Arabidopsis</i> <i>pin1</i> mutants by <i>LhPIN3</i>, driven by the cauliflower mosaic virus 35S promoter, fully restored the root length and number of flowers of the <i>pin1</i> mutant. Overall, our findings reveal that <i>LhPIN3</i> has similar capacities to regulate the root length and number of flowers of <i>Arabidopsis</i> with <i>AtPIN1</i>.
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