Modulation of acc synthase improves plant yield under low nitrogen conditions

Abstract

The invention provides methods for improving plant yield, particularly under nitrogen limiting conditions. According to the invention, applicants have discovered that modulating ACC synthase activity in plants improves yield of plants, even when grown under low nitrogen conditions. The same plants, while demonstrating improved yield over non-modified plants, exhibited no deleterious effects under normal nitrogen conditions. The invention further provides methods using recombinant expression cassettes, host cells and transgenic plants.

That which is claimed: 
     
         1 . A method of improving nitrogen stress tolerance in a maize plant comprising:
 a) inhibiting ethylene synthesis in a plant by introducing into a maize plant a heterologous polynucleotide that reduces the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase 6 (ACS6) upon expression of said heterologous polynucleotide;   wherein said heterologous polynucleotide comprises a nucleic acid selected from the group consisting of:
 i) a nucleic acid comprising a maize ACS6 nucleic acid; 
 ii) a nucleic acid comprising at least 15 contiguous nucleotides of the complement of a maize ACS6 nucleic acid; and 
 iii) a nucleic acid encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of a maize ACS6 nucleic acid, wherein said nucleic acid comprises:
 (1) a first nucleotide sequence comprising at least 21 contiguous nucleotides of a maize ACS6 nucleic acid; and 
 (2) a second nucleotide sequence comprising the complement of said first nucleotide sequence; 
 
   b) growing said plant under nitrogen limiting conditions; and   c) selecting plants exhibiting greater tolerance to low nitrogen levels, whereby said heterologous polynucleotide is expressed and said plant demonstrates improved nitrogen stress tolerance comprising reduced anthesis-silking interval, reduced barren count, and/or increased biomass, compared to a control plant.   
     
     
         2 . The method of  claim 1 , wherein said heterologous polynucleotide comprises a nucleotide sequence selected from the group consisting of:
 a) the nucleotide sequence set forth in SEQ ID NO: 2 or 5, or complete complement thereof;   b) a nucleotide sequence having at least 90% sequence identity to SEQ ID NO: 2 or 5, or a complete complement thereof;   c) a nucleotide sequence encoding the polypeptide sequence of SEQ ID NO: 8, or a complete complement thereof;   d) a nucleotide sequence encoding a polypeptide sequence having at least 95% identity to SEQ ID NO: 8, or a complete complement thereof;   e) a nucleotide sequence comprising at least 15 contiguous nucleotides of the complement of SEQ ID NO: 2 or 5; and   f) a nucleotide sequence encoding a transcript that is capable of forming a double-stranded RNA and mediating RNA interference of an ACC synthase nucleic acid, wherein said nucleotide sequence comprises at least 21 contiguous nucleotides of SEQ ID NO: 2 or 5, and the complement thereof.   
     
     
         3 . The method of  claim 2 , wherein said plant comprises an endogenous mRNA transcribed from a polynucleotide having the sequence set forth in SEQ ID NO: 2 or 5, wherein expression of said heterologous polynucleotide inhibits the expression of the endogenous mRNA. 
     
     
         4 . The method of  claim 1 , wherein said heterologous polynucleotide is operably linked to a promoter that functions in plants. 
     
     
         5 . The method of  claim 4 , wherein the promoter that functions in plants is a tissue-preferred promoter, tissue-specific promoter, or an inducible promoter. 
     
     
         6 . A recombinant expression cassette comprising a nucleotide sequence selected from the group consisting of:
 a) the nucleotide sequence set forth in SEQ ID NO: 51;   b) the nucleotide sequence set forth in SEQ ID NO: 52   c) the nucleotide sequence set forth in SEQ ID NO: 53;   d) the nucleotide sequence set forth in SEQ ID NO: 54;   c) the nucleotide sequence set forth in SEQ ID NO:55;   d) the nucleotide sequence set forth in SEQ ID NO:56; and   e) the nucleotide sequence set forth in SEQ ID NO:57.   
     
     
         7 . A plant cell comprising the recombinant expression cassette of  claim 6 . 
     
     
         8 . The plant cell of  claim 7 , wherein the plant cell is from  Zea mays , wheat, rice,  sorghum , barley, oat, lawn grass, rye, soybean, sugarcane,  Brassica  or sunflower. 
     
     
         9 . A plant regenerated from the plant cell of  claim 8 . 
     
     
         10 . A method of inhibiting ethylene production in a plant, the method comprising inhibiting expression of one or more ACC synthase genes in the plant by introducing into the plant a heterologous polynucleotide having a nucleotide sequence selected from the group consisting of:
 a) the nucleotide sequence set forth in SEQ ID NO: 51;   b) the nucleotide sequence set forth in SEQ ID NO: 52;   c) the nucleotide sequence set forth in SEQ ID NO: 53;   d) the nucleotide sequence set forth in SEQ ID NO: 54;   e) the nucleotide sequence set forth in SEQ ID NO: 55;   f) the nucleotide sequence set forth in SEQ ID NO: 56;   g) the nucleotide sequence set forth in SEQ ID NO: 57; and   h) the nucleotide sequences set forth in SEQ ID NO:51 and 52.