A Role for Flavin Monooxygenase-Like Enzymes in Auxin Biosynthesis

Abstract

Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominant Arabidopsis mutant, yucca, which contains elevated levels of free auxin. YUCCA encodes a flavin monooxygenase-like enzyme and belongs to a family that includes at least nine other homologous Arabidopsis genes, a subset of which appears to have redundant functions. Results from tryptophan analog feeding experiments and biochemical assays indicate that YUCCA catalyzes hydroxylation of the amino group of tryptamine, a rate-limiting step in tryptophan-dependent auxin biosynthesis.

Auxin Control in the Formation of Adventitious Roots

“…Recently, it has been shown using notabilis mutant that adventitious root phenotype can be restored to wild type by expressing the LeNCED1 gene involved in ABA biosynthesis, suggesting that ABA can be a negative regulator of adventitious roots (Thompson et al, 2004). Mutants overproducing auxin in Arabidopsis, like sur1 and sur2 (Boerjan et al, 1995;Delarue et al, 1998) or yucca (Zhao et al, 2001) produce adventitious roots on hypocotyls of light grown seedlings. SUR1 and SUR2 genes encode a C-S-lyase protein and the cytochrome P450 Cyp83B1, both involved in the indole glucosinolate pathway (Bak et al, 2001;Barlier et al, 2000;Mikkelsen et al, 2004).…”

“…SUR1 and SUR2 genes encode a C-S-lyase protein and the cytochrome P450 Cyp83B1, both involved in the indole glucosinolate pathway (Bak et al, 2001;Barlier et al, 2000;Mikkelsen et al, 2004). YUCCA1 gene encodes a flavin monooxygenase suitable for converting tryptamine in N-hydroxyl tryptamine in vitro (Zhao et al, 2001(Zhao et al, , 2002) and belongs to a family of YUCflavin mono-oxigenases from which 4 have a role in auxin biosynthesis (Cheng et al, 2006).…”

COP1 mediates the coordination of root and shoot growth by light through modulation of PIN1- and PIN2-dependent auxin transport in Arabidopsis

“…The plant hormone auxin (indole-3-acetic acid; IAA) plays a major role in morphogenesis and mediates some of the growth responses to light, including hypocotyl elongation, apical hook maintenance, phototropic responses and the shade avoidance syndrome (Boerjan et al, 1995;Zhao et al, 2001;Stepanova et al, 2008;Esmon et al, 2006;Tao et al, 2008). Auxin action depends on a tightly regulated distribution across the plant.…”

The BUD2 mutation affects plant architecture through altering cytokinin and auxin responses in Arabidopsis

“…In many plant species, axillary buds become dormant due to the inhibiting effects of the primary shoot apex on the outgrowth of AMs, a phenomenon known as 'apical dominance'. Auxin was first regarded as a direct regulator in this process [14], a notion strengthened thereafter by physiological studies on decapitated shoot apices [15][16][17], and by analyzing auxin biosynthesis, transport and signaling [18][19][20][21][22][23][24][25][26][27][28][29] in plants. However, when radiolabelled auxin was applied to a decapitated stump, the outgrowth of axillary buds was inhibited even though radiolabelled auxin was not found to accumulate in axillary buds, suggesting an indirect suppression effect of auxin on the AM outgrowth [28,30] and the presence of second messengers.…”