The flooding resilience loci SUBMERGENCE 1 and ANAEROBIC GERMINATION 1 interact in rice seedlings established underwater

Little is known of the consequences of genetic pyramiding of abiotic stress tolerance loci in crops. In rice (Oryza sativa L.), ANAEROBIC GERMINATION1 (AG1) encodes TREHALOSE 6-PHOSPHATE PHOSPHATASE 7 (OsTPP7) that enhances mobilization of endosperm reserves to the embryo, promoting formation of a highly elongated hollow coleoptile in seeds sown directly into shallow paddies. This trait reduces labor costs and herbicide use. SUBMERGENCE1 (SUB1) includes the ethylene-responsive transcription factor SUB1A that confers tolerance to complete submergence by dampening shoot elongation of vegetative-phase plants and enhancing regrowth upon desubmergence. As OsTPP7 and SUB1A-1 mRNAs simultaneously accumulate in shoots, we evaluated the independent contribution and interactions between these loci in rice seeded under complete submergence until the four-leaf stage (14 d). Evaluating growth, carbohydrates, and the transcriptome of shoot tissue of four near-isogenic genotypes uncovered independent and interacting effects including: (a) early enhanced coleoptile elongation by IR64(AG1); (b) precocious transition to phototrophy followed by limited elongation by IR64(SUB1); and (c) delayed phototrophy by IR64(AG1, SUB1). mRNA-sequencing highlighted time-dependent and genotype-specific regulation of mRNAs associated with energy sensing, carbohydrate catabolism, photomorphogenesis, elongation, and defense responses. Although SUB1A did not antagonize AG1 in direct seeding, seedling establishment could be negatively impacted if submergence escape does not occur before the transition to photoautotrophy, due to antithetical regulation of carbohydrate catabolism by AG1 and SUB1. 45 samples in total - 3 replicates, 4 genotypes, 1 RNA populations, 2-14 days treatment: Oryza sativa coleoptile 4-days-old, Oryza sativa coleoptile 8-days-old, Oryza sativa coleoptile 14-days-old, Oryza sativa embryo 2-days-old.