Nanoridges that characterize the surface morphology of flowers require the synthesis of cutin polyester

Abstract

Distinctive nanoridges on the surface of flowers have puzzled plant biologists ever since their discovery over 75 years ago. Although postulated to help attract insect pollinators, the function, chemical nature, and ontogeny of these surface nanostructures remain uncertain. Studies have been hampered by the fact that no ridgeless mutants have been identified. Here, we describe two mutants lacking nanoridges and define the biosynthetic pathway for 10,16-dihydroxypalmitate, a major cutin monomer in nature. Using gene expression profiling, two candidates for the formation of floral cutin were identified in the model plant Arabidopsis thaliana: the glycerol-3-phosphate acyltransferase 6 (GPAT6) and a member of a cytochrome P450 family with unknown biological function (CYP77A6). Plants carrying null mutations in either gene produced petals with no nanoridges and no cuticle could be observed by either scanning or transmission electron microscopy. A strong reduction in cutin content was found in flowers of both mutants. In planta overexpression suggested GPAT6 preferentially uses palmitate derivatives in cutin synthesis. Comparison of cutin monomer profiles in knockouts for CYP77A6 and the fatty acid -hydroxylase CYP86A4 provided genetic evidence that CYP77A6 is an in-chain hydroxylase acting subsequently to CYP86A4 in the synthesis of 10,16-dihydroxypalmitate. Biochemical activity of CYP77A6 was demonstrated by production of dihydroxypalmitates from 16-hydroxypalmitate, using CYP77A6-expressing yeast microsomes. These results define the biosynthetic pathway for an abundant and widespread monomer of the cutin polyester, show that the morphology of floral surfaces depends on the synthesis of cutin, and identify target genes to investigate the function of nanoridges in flower biology.10,16-dihydroxypalmitic acid ͉ cuticular ridges ͉ CYP77A6 ͉ CYP86A4 ͉ glycerol-3-phosphate acyltransferase 6

Physical Interaction of Floral Organs Controls Petal Morphogenesis in Arabidopsis

“…A series of Arabidopsis mutants defective in cuticle synthesis and secretion show the biological roles of cuticles as a barrier to biotic or abiotic stresses, osmotic stress, water loss, and damage from UV radiation, and in preventing the fusion of leaves and floral organs (Yephremov et al, 1999;Pruitt et al, 2000;Krolikowski et al, 2003;Aharoni et al, 2004;Kurdyukov et al, 2006;Bessire et al, 2007;Shi et al, 2011;Wang et al, 2011). Some mutants are known to be involved in petal morphogenesis: Lack of nanoridges of petals, due to a mutation in DEFECTIVE IN CUTICULAR RIDGES (DCR, encoding a BAHD acyltransferase), CYP77A6 (cytochrome P450 family), GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE6 (GPAT6), or PERMEABLE CUTICLE1 (PEC1), result in increased permeability of petals to a dye and cause organ fusion (Li-Beisson et al, 2009;Panikashvili et al, 2009;Bessire et al, 2011). Compared with these Left and right halves show the petal structure in the wild type and fop1, respectively.…”

Cytochrome P450 CYP94B3 mediates catabolism and inactivation of the plant hormone jasmonoyl-L-isoleucine

“…Microsomal protein was quantified with BCA protein assay reagent (Pierce). In vitro hydroxylation assays were performed as described by Li-Beisson et al (44), with minor modifications. JA-Ile substrate consisting of a mixture of the (3R, 7R) and (3R, 7S) stereoisomers in ethanol (8), was evaporated in a microfuge tube and redissolved in 2 μL DMSO.…”

Analyses of Tomato Fruit Brightness Mutants Uncover Both Cutin-Deficient and Cutin-Abundant Mutants and a New Hypomorphic Allele of GDSL Lipase

“…In recent years, availability of the Arabidopsis (Arabidopsis thaliana) genome sequence, high-throughput gene expression analysis tools, and mutant collections enabled deciphering the biosynthetic pathways and transport networks involved in cutin, suberin, and wax biosynthesis (Pollard et al, 2008;Li-Beisson et al, 2009;Beisson et al, 2012;Yeats and Rose, 2013). The synthesis of the cutin monomer starts with the synthesis of long chain fatty acids in the plastids.…”

“…The synthesis of the cutin monomer starts with the synthesis of long chain fatty acids in the plastids. Fatty acids are then transported to the cytoplasm where they undergo a series of modifications, including the activation to CoA thioesters by long chain acyl-CoA synthetases, oxidation by cytochrome P450 (CYP)-dependent fatty acid oxidases, and esterification to glycerol-based acceptors by glycerol-3-phosphate acyl transferases to produce acyl-glycerols (Pollard et al, 2008;Li-Beisson et al, 2009). Although the sequential order of the reactions remains to be determined, the implication of several long chain acyl-CoA synthetases, CYP86A, CYP77A, and glycerol-3-phosphate acyl transferases in cutin biosynthesis has been confirmed in Arabidopsis.…”