Expression of thermostable starch synthase genes improves the yield in heat stress

Abstract

Genetically-modified plants having increased tolerance to heat stress are described. Methods of producing such genetically-modified plants are also disclosed. The genetically-modified plants comprise exogenous nucleic acid encoding a thermostable protein having starch synthase activity. Genetically-modified plants have increased yield when grown under elevated conditions as compared to control plants.

1 . A genetically-modified plant having increased tolerance to heat stress as compared to a control plant, said genetically-modified plant comprising exogenous nucleic acid encoding a thermostable protein having starch synthase activity. 
     
     
         2 . The genetically-modified plant of  claim 1 , wherein said thermostable protein maintains starch synthase activity at temperatures greater than 25° C. 
     
     
         3 . The genetically-modified plant of  claim 1 , said genetically-modified plant having increased yield as compared to said control plant when plants are grown under heat stress, wherein said increased yield is selected from the group consisting of an increase in total seed weight, increased thousand kernel weight, increased biomass, and combinations thereof. 
     
     
         4 . (canceled) 
     
     
         5 . The genetically-modified plant of  claim 1 , wherein said plant comprises an endogenous protein having starch synthase activity, said endogenous protein having a first relative thermostability, and said thermostable protein having a second relative thermostability, wherein said second relative thermostability is greater than said first relative thermostability. 
     
     
         6 . The genetically-modified plant of  claim 1 , wherein said plant is selected from the group consisting of grains, tubers, and legumes. 
     
     
         7 . The genetically-modified plant of  claim 1 , wherein said genetically-modified plant is of a first plant species, and wherein said thermostable protein having starch synthase activity is native to a second plant species, said first plant species being different from said second plant species. 
     
     
         8 . (canceled) 
     
     
         9 . The genetically-modified plant of  claim 7 , wherein said second plant species is selected from the group consisting of rice, cottonwood, grape,  sorghum , soybean, maize, beans, algae, clover, amaranth, arabidopsis, cocoa, tomato, cassava, alfalfa, common bean, chickpea, and peach. 
     
     
         10 . The genetically-modified plant of  claim 7 , wherein said first plant species is selected from the group consisting of wheat, oat, barley, rice, maize, millet, rye,  sorghum , triticale, buckwheat, quinoa, soybeans, beans, peas, alfalfa, potatoes, sweet potatoes, cassava, and yam. 
     
     
         11 . The genetically-modified plant of  claim 1 , said nucleic acid encoding a thermostable starch synthase protein comprising the amino acid sequence of SEQ ID NO: 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, or thermostable starch synthase protein having at least about 50% amino acid identity to SEQ ID NO: 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, and retaining the functional characteristics thereof. 
     
     
         12 . The genetically-modified plant of  claim 1 , wherein said nucleic acid comprises: (a) a nucleotide sequence of SEQ ID NO:1, 3, 5, or 7; or (b) a nucleotide sequence having at least about 70% sequence identity to SEQ ID NO:1, 3, 5, or 7. 
     
     
         13 . (canceled) 
     
     
         14 . A method of increasing tolerance to heat stress in a plant, said method comprising:
 transforming a plant with an exogenous nucleic acid encoding a thermostable protein having starch synthase activity to yield a transformed plant, thereby increasing the heat stress tolerance of said transformed plant.   
     
     
         15 . The method of  claim 14 , wherein said transforming comprising:
 introducing into said plant a nucleic acid construct comprising said nucleic acid encoding a thermostable protein having starch synthase activity, said nucleic acid construct expressing starch synthase in said transformed plant.   
     
     
         16 . The method of  claim 15 , wherein said nucleic acid is operably linked to a promoter that drives expression in a plant cell. 
     
     
         17 . (canceled) 
     
     
         18 . The method of  claim 15 , wherein said nucleic acid is synthesized from a starch synthase gene isolated from a thermotolerant plant and cloned into said construct prior to said introducing. 
     
     
         19 .- 21 . (canceled) 
     
     
         22 . The method of  claim 14 , wherein said plant comprises a plant tissue, and said transforming comprising:
 culturing said tissue on media;   introducing said exogenous nucleic acid into the cells of said tissue to yield transformed tissue;   inducing callus formation from said transformed tissue;   regenerating shoots; and   rooting of said shoots in rooting media to regenerate said whole plant.   
     
     
         23 .- 24 . (canceled) 
     
     
         25 . The method of  claim 22 , wherein said introducing is selected from the group consisting of:  Agrobacterium -mediated transformation, PEG-mediated uptake, electroporation-mediated uptake, particle bombardment-mediated delivery, viral infection, and/or microinjection. 
     
     
         26 . The method of  claim 14 , further comprising growing said transformed plant under elevated growing conditions, wherein said transformed plant has increased yield as compared to a control plant grown under said elevated growing conditions. 
     
     
         27 . A genetically-modified seed produced from a transformed plant according to the method of  claim 14 . 
     
     
         28 . (canceled) 
     
     
         29 . A method of producing genetically-modified plants having increased tolerance to heat stress as compared to a control plant, said method comprising: crossing a first parent plant with a second parent plant to thereby produce progeny, wherein at least one of said first or second parent plants is a genetically-modified plant according to  claim 1 , said progeny having increased tolerance to heat stress as compared to a control plant. 
     
     
         30 .- 33 . (canceled) 
     
     
         34 . A recombinant plant cell having ectopic expression of an exogenous thermostable protein having starch synthase activity by stable transformation with a nucleic acid construct encoding said thermostable protein. 
     
     
         35 . The recombinant plant cell of  claim 34 , wherein said thermostable protein comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, or has at least about 50% amino acid identity to a sequence selected from the group consisting of SEQ ID NO: 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, and retaining the functional characteristics thereof. 
     
     
         36 . The recombinant plant cell of  claim 34 , wherein said nucleic acid construct comprises: (a) a nucleotide sequence of SEQ ID NO:1, 3, 5, or 7; or (b) a nucleotide sequence having at least about 70% sequence identity to SEQ ID NO:1, 3, 5, or 7.