Genomic sequencing revealed that a 445 bp retrotransposon was inserted into the 2nd exon of LOC_Os10g36924 in the dte1 mutant ( Fig. 3B, Suppl. Fig. S4A) leading to a frame-shift that produced a premature stop codon ( Fig. 3B). If translated, the mutant transcript would encode a truncated protein with 183 amino acids of the C-terminal of LOC_Os10g36924 being replaced by 20 amino acids derived from the retrotransposon sequence (Suppl. Fig. S4B). Expression analysis showed that LOC_Os10g36924 was sharply down-regulated in the dte1 mutant ( Fig. 3C), suggesting that LOC_Os10g36924 was most likely the candidate gene underlying the dte1 mutation.
To confirm the identity of DTE1/LOC_Os10g36924 we performed genetic complementation by expressing the entire LOC_Os10g36924 coding sequence plus its native promoter in the dte1 mutant. In the positive transgenic lines the morphological traits of tiller number, plant height, and seed fertility were restored to the levels of wild type when grown at the HNLB site ( Fig. 3D). In addition, we also constructed an RNAi vector of DTE1 and transformed it into japonica cv. Kitaake. Notably, all positive transgenic plants grown in B-deficient media displayed phenotypes similar to those of the dte1 mutant (Suppl. Fig. S5A). The expression levels of DTE1 were consistent with those of the corresponding phenotypes in complementary and RNAi plants (Suppl. Fig. S5B and C). We concluded that the abnormal phenotypes of the dte1 mutant resulted from mutation of LOC_Os10g36924/DTE1.