Abstract
NITRIC OXIDE-ASSOCIATED1 (NOA1) encodes a circularly permuted GTPase (cGTPase) known to be essential for ribosome assembly in plants. While the reduced chlorophyll and Rubisco phenotypes were formerly noticed in both NOA1-supressed rice and Arabidopsis, a detailed insight is still necessary. In this study, by using RNAi transgenic rice, we further demonstrate that NOA1 functions in a temperature-dependent manner to regulate chlorophyll and Rubisco levels. When plants were grown at 30°C, the chlorophyll and Rubisco levels in OsNOA1-silenced plants were only slightly lower than those in WT. However, at 22°C, the silenced plants accumulated far less chlorophyll and Rubisco than WT. It was further revealed that the regulation of chlorophyll and Rubisco occurs at the anabolic level. Etiolated WT seedlings restored chlorophyll and Rubisco accumulations readily once returned to light, at either 30°C or 15°C. Etiolated OsNOA1-silenced plants accumulated chlorophyll and Rubisco to normal levels only at 30°C, and lost this ability at low temperature. On the other hand, de-etiolated OsNOA1-silenced seedlings maintained similar levels of chlorophyll and Rubisco as WT, even after being shifted to 15°C for various times. Further expression analyses identified several candidate genes, including OsPorA (NADPH: protochlorophyllide oxidoreductase A), OsrbcL (Rubisco large subunit), OsRALyase (Ribosomal RNA apurinic site specific lyase) and OsPuf4 (RNA-binding protein of the Puf family), which may be involved in OsNOA1-regulated chlorophyll biosynthesis and Rubisco formation. Overall, our results suggest OsNOA1 functions in a temperature-dependent manner to regulate chlorophyll biosynthesis, Rubisco formation and plastid development in rice.
Highlights
Nitric oxide (NO) functions in plant defense responses, and in the regulation of various plant developmental processes, including germination, root growth, vascular differentiation, stomatal closure, and flowering [1]
Generation of the OsNOA1-silenced lines Examination of the rice genome identified a single gene (Os02g0104700) that is homologous to AtNOS1 to NO-associated protein 1 (AtNOA1)/RIF1, which we named OsNOA1
OsNOA1 has an open reading frame (ORF) of 1644 bp that encodes a protein of 547 amino acids with 62% similarity to AtNOA1/RIF1
Summary
Nitric oxide (NO) functions in plant defense responses, and in the regulation of various plant developmental processes, including germination, root growth, vascular differentiation, stomatal closure, and flowering [1]. The mechanism underlying nitric oxide (NO) synthesis has been well established in animals, and depends primarily on a heme-flavoprotein NO synthase (NOS). NOS1 in Arabidopsis (AtNOS1) was first characterized as a potential nitric oxide synthase, which shares homology to a hypothetical snail NOS or NOS partner [3]. NO levels in Atnos1-knockout mutants were significantly reduced compared to WT plants [3,4,5], and the yellowish phenotype of the Atnos mutants was partially rescued by the application of NO donor compounds [3,6,7]. The NOS1-deficient plants showed decreased NO accumulation in response to ABA, salicylic acid, salinity, and elicitor treatments [4,5,8,9,10]
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