Genome-Wide Identification and Analysis on YUCCA Gene Family in Isatis indigotica Fort. and IiYUCCA6-1 Functional Exploration

Abstract

Auxin is one of the most critical hormones in plants. YUCCA (Tryptophan aminotransferase of <i>Arabidopsis</i> (TAA)/YUCCA) enzymes catalyze the key rate-limiting step of the tryptophan-dependent auxin biosynthesis pathway, from IPA (Indole-3-pyruvateacid) to IAA (Indole-3-acetic acid). Here, 13 YUCCA family genes were identified from <i>Isatis indigotica</i>, which were divided into four categories, distributing randomly on chromosomes (2<i>n</i> = 14). The typical and conservative motifs, including the flavin adenine dinucleotide (FAD)-binding motif and flavin-containing monooxygenases (FMO)-identifying sequence, existed in the gene structures. <i>IiYUCCA</i> genes were expressed differently in different organs (roots, stems, leaves, buds, flowers, and siliques) and developmental periods (7, 21, 60, and 150 days after germination). Taking <i>IiYUCCA6-1</i> as an example, the <i>YUCCA</i> genes functions were discussed. The results showed that <i>IiYUCCA6-1</i> was sensitive to PEG (polyethylene glycol), cold, wounding, and NaCl treatments. The over-expressed tobacco plants exhibited high auxin performances, and some early auxin response genes <i>(NbIAA8, NbIAA16, NbGH3.1</i>, and <i>NbGH3.6</i>) were upregulated with increased IAA content. In the dark, the contents of total chlorophyll and hydrogen peroxide in the transgenic lines were significantly lower than in the control group, with <i>NbSAG12</i> downregulated and some delayed leaf senescence characteristics, which delayed the senescence process to a certain extent. The findings provide comprehensive insight into the phylogenetic relationships, chromosomal distributions, and expression patterns and functions of the YUCCA gene family in <i>I. indigotica</i>.