## 3 Discussion
Localizations of twelve rice PTs were confirmed, with five mainly in chloroplasts, one dually in chloroplasts and mitochondria and six in cytosol in rice cells (Figure 5). Within chloroplasts, OsGPS, OsGGPS1 and OsGRP were mainly localized into plastglobules, even though they were also observed in stroma (Figure 6A) and OsSPS1 to 3 existed in stroma (Figure 6B). In contrast to other plastidial GPS/GGPS homologous from _Arabidopsis_ and _Catharanthus roseus_ that are mainly active in stroma [14; 42], rice GPS/GGPS families peculiarly seem to take plastoglobules as the main venue for the biosynthesis of GPP and GGPP, and supply the primary substrates of monoterpenes, diterpenes, tetraterpenes and long chain-PPs. As with other plastidial PTs in rice, OsSPS2 and OsSPS3 were mainly observedin stroma of rice protoplasts, but not in plastoglobules (Figure 6B) and the plastitial localization of OsSPS2 was also observed in tobacco leaf cells [20]. Other studies reported that OsSPS1 was targeted only in mitochondria of onion and tobacco leaf cells [20], however, OsSPS1 was dual-localized in both mitochondria and chloroplasts in this study and AtPPS1 (AAW39025) with close relation to OsSPS1 in our phylogenetic tree was similarly dual-localized into mitochondria and stroma [43], supporting their similar functions in mitochondria and chloroplasts. Another SPS, OsSPS4, was localized in cytosol with spot-like patterns, regarded as cytosolic vesicles (Figure 6B). Taken together, GPP/GGPPs are supposed to be produced in plastoglobules as main venues and also in stroma and SPP/PPPs are regarded to exist in chloroplasts, mitochondria and cytosolic vesicles. As summarized in Table 1, GPP/GGPP can be produced by both OsGPS and OsGGPS1 in rice. OsGPS not only biosynthesize mainly GPP, but can also produce GGPP under the limited conditions in which FFP is present as a substrate, and likewise, OsGGPS1 can also produce the limited amount of GPP in addition to GGPP [10]. OsSPS1 and OsSPS2 were reported to produce SPP/PPP by using the primary substrates such as GPP, FFP and GGPP [20], OsSPS3 [21] and OsSPS4 were identified as the putative SPS family proteins. The FFP was predictably produced by five kinds of OsFPSs in this study and two previous studies [22; 24]. As the next step, we have further considered the important roles of rice PTs in supplying the primary substrates (GPP/FFP/GGPP) to terpene biosynthetic enzymes. As shown in Figure 5, the expression of OsTPS19 is strongly increased by meJA-treatment with OsGPS, which utilizes GPP as a substrate for producing monoterpenes such as limonene and linalool [35], but it was reported that OsTPS19 existed in stroma [35], in contrast to the localization of OsGPS to PGs (Figure 6). If so, how can GPPs be supplied to OsTPS19 for monoterpene production? Firstly, an OsGGPS1 existing in stroma could be regarded as the GPP-supplier of OsTPS19, which of expression is induced by meJA treatment, and as another possibility, it could be also considered that an OsGPS or OsTPS19 might be translocated into stroma or PGs or GPPs itself might be transported into stroma from PGs. The ABA-induced OsGGPS1 and OsPSY2 are similarly observed in both stroma and PGs (Figures 5 and 6A), suggesting that OsGGPS1 has functions on supplying GGPP to OsPSY1,2,3, considered with the previous report that OsPSY1,2,3 were mainly localized in chloroplast stroma and PGs [44]. Additionally, in a previous study, OsSPS1 preferentially utilized FFP as a main substrate for SPP biosynthesis, compared to GPP or GGPP as minor allylic substrates [20]. As well, OsGPS was reported to limitedly produce GGPP in vitro under the condition that FFP was supplied as an allylic substrate [10]. As the cases stand, the possibility of FFP in chloroplast could not be ruled out, even if the existence of FFP in chloroplasts has been still largely unknown. If so, a question arises of how FPP is supplied to OsSPS1 and OsGPS for SPP and GGPP production in chloroplasts, respectively.