# Rice Sesquierpene Plays Important Roles in Antixenosis against Brown Planthopper in Rice
## 2 Results and Discussion
### The Seven Amino Acid Deletion in OsSTPS2 Is a Natural Variation  
The KD allele of the _OsSTPS2_ gene contained two SNPs--TG > CA--in exon 5, leading to 21 bp and seven amino acid deletions in the mRNA and protein sequence, respectively. To investigate whether these two SNPs were found in other rice varieties, genomic DNA harboring this region of the gene was amplified from several rice varieties, and the sequences (accession no KP117047 to KP117059) were aligned. Interestingly, it was found that not only KD but also PK2, PK3, RBR, and HCS contained these two SNPs in exon 5 of the gene (Table 1, Figure S2). However, Mudge, TN1, Pokkali, ARC10550, ASD7, JHN, and Nipponbare contained the TG nucleotides in the same manner as PTB33 and ILs, but the 21 bp deletion occurred in the genomic DNA of these varieties. The _OsSTPS2_ genes expressed by nine rice varieties and three ILs (IL143, IL302, and IL308) were sequenced (accession no. KC511057 to KC511068). Interestingly, it was found that not only KD but also JHN, TN1, Mudge, Pokkali, ARC10550, ASD7, and Nipponbare have this 21 bp deletion in their allele of the gene (Table 1, Figure S2). On the other hand, the 21 bp deletion was not found in the alleles of BPH-resistant varieties such as PTB33, Pitsanulok 2 (PL2), and all ILs tested. The deduced amino acid sequences of these varieties were translated, and the seven amino acid deletion was found in JHN, TN1, Mudge, Pokkali, ARC10550, ASD7, and Nipponbare, respectively (Figure S2). This finding suggests that not only KD but some other rice varieties, both BPH-resistant and susceptible, also contain seven amino acid deleted lesions in the _OsSTPS2_ gene.  
Antixenosis Mechanism Is Not Functional in Rice Varieties Harboring a Seven Amino Acid Deletion in the _OsSTPS2_ Gene  
To elucidate the effect of the seven amino acid deletion in the deduced protein sequence of the _OsSTPS2_ gene on its putative function in the antxenosis of BPH feeding preference (AFP), five rice varieties/lines were selected for AFP study: JHN, Mudge, ASD7, Pokkali, and IL308. The _OsSTPS2_ gene was expressed in all these rice varieties/lines, but the seven amino acid deletion was found only in JHN, Mudge, ASD7, and Pokkali. The BPH damage score reaction against the BPH population from Ubon Rachathani (UBN-BPH) showed that IL308 and Pokkali were BPH resistant, Mudge and ASD7 were moderately susceptible, and JHN was BPH susceptible (Figure 2, Supplementary Table S1). The AFP comparison between IL308 and other rice varieties revealed that in all combinations, BPH preferred to settle on Mudge, Pokkali, JHN, and ASD7 than on IL308, respectively (Figure 3A-D, Table S2). Even though both IL308 and Pokkali were BPH resistant (with scores of 0.7 and 1.7, respectively), the AFP test clearly demonstrated that, over the 96 h period of BPH infestation, BPHs preferred Pokkali to IL308. The AFP comparisons between JHN, the BPH-susceptible variety, and other rice varieties are shown in Figure 3E-G. Interestingly, the AFP comparison revealed that even though JHN was the most susceptible rice variety in this group, BPHs randomly settled on the tested plants over the 96 h period of the BPH settling choice test. The results from the AFP experiments demonstrated that the putative function of the _OsSTPS2_ gene in the antxenosis mechanism is regulated not only at the transcription level by sequence variation at the promoter region of the gene, but also at the translation level in a process by which rice varieties containing the allele with the seven amino acid deletion were unable to proceed with the antxenosis mechanism during BPH infestation.