Abstract
Although adenosine monophosphate (AMP) binding domain is widely distributed in multiple plant species, detailed molecular functions of AMP binding proteins (AMPBPs) in plant development and plant-pathogen interaction remain unclear. In the present study, we identified an AMPBP OsAAE3 from a previous analysis of early responsive genes in rice during Magnaporthe oryzae infection. OsAAE3 is a homolog of Arabidopsis AAE3 in rice, which encodes a 4-coumarate-Co-A ligase (4CL) like protein. A phylogenetic analysis showed that OsAAE3 was most likely 4CL-like 10 in an independent group. OsAAE3 was localized to cytoplasm, and it could be expressed in various tissues. Histochemical staining of transgenic plants carrying OsAAE3 promoter-driven GUS (β-glucuronidase) reporter gene suggested that OsAAE3 was expressed in all tissues of rice. Furthermore, OsAAE3-OX plants showed increased susceptibility to M. Oryzae, and this finding was attributable to decreased expression of pathogen-related 1a (PR1) and low level of peroxidase (POD) activity. Moreover, OsAAE3 over-expression resulted in increased content of H2O2, leading to programmed cell-death induced by reactive oxygen species (ROS). In addition, OsAAE3 over-expression repressed the floret development, exhibiting dramatically twisted glume and decreased fertility rate of anther. Meanwhile, the expressions of lignin biosynthesis genes were significantly decreased in OsAAE3-OX plants, thereby leading to reduced lignin content. Taken together, OsAAE3 functioned as a negative regulator in rice blast resistance, floret development, and lignin biosynthesis. Our findings further expanded the knowledge in functions of AMBPs in plant floret development and the regulation of rice-fungus interaction.
Highlights
Adenosine monophosphate (AMP) binding domain-containing proteins widely exist in various plant species, and this family consists of members with diverse functions, including luciferases, peptide antibiotic synthetases, acetyl-coenzyme A (CoA) synthetases (ACSs), acyl-CoA synthetases, 4-coumarateCoA ligases (4CLs), and various other closely-related synthetases (Shockey et al, 2000; OsAAE3 Regulates Lignin BiosynthesisStremmel et al, 2001; Shockey and Browse, 2011)
The most closely related proteins are 4CL like proteins in Arabidopsis, which exhibited 90% sequence similarity to AAE3, suggesting that OsAAE3 had probably evolved into a subsidiary enzyme of 4CL (Figure S1)
This clearly stated that OsAAE3 was different from Os4CLs in biological function according to observed phenotype of OsAAE3-OX plants. 4CL ligates coenzyme A (CoA) with hydroxycinnamic acids, such as 4-coumaric and caffeic acids, into hydroxycinnamoyl-CoA thioesters, and these reactions accelerate the process of monolignol biosynthesis for lignification in plant cell walls (Chen et al, 2013)
Summary
Adenosine monophosphate (AMP) binding domain-containing proteins widely exist in various plant species, and this family consists of members with diverse functions, including luciferases, peptide antibiotic synthetases, acetyl-CoA synthetases (ACSs), acyl-CoA synthetases, 4-coumarateCoA ligases (4CLs), and various other closely-related synthetases (Shockey et al, 2000; OsAAE3 Regulates Lignin BiosynthesisStremmel et al, 2001; Shockey and Browse, 2011). Free fatty acids released from the plastids become metabolically available when they are converted to their corresponding Co-A thioesters (Li et al, 2015) This activation is induced by long-chain acyl-coenzyme asynthetases (LACSs). The expression of rice OsBIABP1 is activated by M. oryzae infection, which may be a defense-related AMP-binding protein (AMPBP) that is involved in the regulation of defense response through SA and/or JA/ET signaling pathways. Functions of those genes remain unexplored in rice (Zhang et al, 2009)
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