Abstract
Auxin is one of the most critical hormones in plants. YUCCA (Tryptophan aminotransferase of Arabidopsis (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 Isatis indigotica, which were divided into four categories, distributing randomly on chromosomes (2n = 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. IiYUCCA 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 IiYUCCA6-1 as an example, the YUCCA genes functions were discussed. The results showed that IiYUCCA6-1 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 (NbIAA8, NbIAA16, NbGH3.1, and NbGH3.6) 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 NbSAG12 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. indigotica.
Highlights
IAA (Indole-3-acetic acid) is the main type of natural auxin in plants, which plays important roles in a series of growth and developmental processes, such as embryonic polarization, vascular bundle differentiation, apical dominance, shoot architecture, root formation, phototropic response, gravity response, and senescence [1,2,3,4,5,6]
The IPA pathway is divided into two steps; tryptophan is transformed into IPA by tryptophan aminotransferase (TAA), and flavin monooxygenase (YUCCA), as the rate-limiting enzyme, catalyzes IPA to IAA [13,14,15]
13 YUCCA genes in total were identified in I. indigotica (Table 1) and the YUCCA genes were named from IiYUCCA1 to IiYUCCA11 (IiYUCCA1, IiYUCCA2, IiYUCCA3, IiYUCCA4, IiYUCCA5-1, IiYUCCA5-2, IiYUCCA6-1, IiYUCCA6-2, IiYUCCA7, IiYUCCA8, IiYUCCA9, IiYUCCA10, IiYUCCA11), referring to the homologous YUCCA sequences in A. thaliana
Summary
IAA (Indole-3-acetic acid) is the main type of natural auxin in plants, which plays important roles in a series of growth and developmental processes, such as embryonic polarization, vascular bundle differentiation, apical dominance, shoot architecture, root formation, phototropic response, gravity response, and senescence [1,2,3,4,5,6]. OsIAA24 and OsIAA20 were up-regulated by high salt stress in Oryza sativa [9], and the expression level of GH3.13 increased under drought treatment, which resulted in IAA content decreasing, with enhanced resistance to drought [10]. 11 YUCCA genes were identified from A. thaliana, providing some evidence for the significant roles of AtYUCCA1, AtYUCCA2, AtYUCCA4, AtYUCCA5, AtYUCCA6, and AtYUCCA7 in the biosynthesis of auxin [13,16,17,18,19]. The auxin functions in regulating growth and development processes for I. indigotica are not as clear as for A. thaliana and other plants [12,16,17,20,24,25,26,27,28]. Sci. 2020, 21, 2188 with a firm foundation for further researches on their functions, adding to the data on YUCCA genes of Cruciferae
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