The Roles of Auxin Biosynthesis YUCCA Gene Family in Plants

Abstract

Auxin plays essential roles in plant normal growth and development. The auxin signaling pathway relies on the auxin gradient within tissues and cells, which is facilitated by both local auxin biosynthesis and polar auxin transport (PAT). The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA)/YUCCA (YUC) pathway is the most important and well-characterized pathway that plants deploy to produce auxin. YUCs function as flavin-containing monooxygenases (FMO) catalyzing the rate-limiting irreversible oxidative decarboxylation of indole-3-pyruvate acid (IPyA) to form indole-3-acetic acid (IAA). The spatiotemporal dynamic expression of different YUC gene members finely tunes the local auxin biosynthesis in plants, which contributes to plant development as well as environmental responses. In this review, the recent advances in the identification, evolution, molecular structures, and functions in plant development and stress response regarding the YUC gene family are addressed.

Keywords: YUCCA; auxin; development; local auxin biosynthesis; stress response.

Figure 1

The auxin biosynthesis pathways identified in plants: Solid arrows indicate pathways in which the enzymes, genes, or intermediates are known, and dashed arrows indicate pathways that are not well defined. The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS /YUCCA (TAA/YUC) pathway is depicted in red. Gene abbreviations of the enzymes catalyzing the metabolic reactions are given in blue upper-case italics. AMI1: amidase 1; ANT: anthranilate; ASA1: anthranilate synthase α subunit 1; ASB1: anthranilate synthase β subunit 1; CYP71A13: indoleacetaldoxime dehydratase 71A13; CYP79B: cytochrome P450 monooxygenase 79B; ESM: epithiospecifier modifier; ESP: epithiospecifier; IAA: indole-3-acetic acid; IAAld: indole-3-acetaldehyde; IAM: indole-3-acetamide; IAN: indole-3-acetonitrile; IAOx: indole-3-acetaldoxime; IGP: indole-3-glycerol phosphate; IGs: indole glucosinolates; INS: indole synthase; IPyA: indole-3-pyruvic acid; l-Trp: l-tryptophan; NITs: nitrilase; SUR: S-alkyl-thiohydroximate lyase; TAA1: tryptophan aminotransferase of Arabidopsis 1; TARs: tryptophan aminotransferases; TDCs: tryptophan decarboxylases; TGG: myrosinase; TRA: tryptamine; TSA: tryptophan synthase subunit A; TSB: tryptophan synthase subunit B; UGT74B1: UDP-glycosyltransferase 74B1; YUCs: YUCCAs.

Figure 2

The molecular structure of flavin-containing monooxygenases (FMO) proteins in plants: Several conserved domains closely related to their functions have been identified, including one flavin adenine dinucleotide (FAD)-binding motif, one GG motif, two ATG-containing motifs, one FMO-identify sequence, and one nicotinamide adenine dinucleotide phosphate (NADPH)-binding motif.