Mechanism Of Regulation On Flowering Time And Spike Architecture By VILs Genes In Brachypodium Distachyon

The flowering transition is regulated by the endogeneous and environmental signals such as the photoperiod, temperature, and age et al., in which epigenetic modification plays an important role. VIN3 family genes, whose expression are affected by environmental factors, together with Polycomb Repressive Complex 2(PRC2) complex, repress key flowering genes by H3K9me2 and H3K27me3 modification in the corresponding chromatin loci. Consequently, the target chromatin were changed into an inhibited state, then the flowering time regulated. Whereas the mechanism of chromatin modification by VIN3 family proteins is relatively conservative in plants, the responding to environment and target genes of VILs differs among different plant groups. In this study, VIN3 Like(VIL) genes in Brachypodium distachyon were comparatively analized. Bd VIL4, 5 RNAi plants were constructed to detect the effect on flowering and other development process. By the assay on Bd VIL4, 5 RNAi plants,the following conclusions were drawn:(1) There are 5 VIL gene loci in the whole genome of Brachypodium distachyon, all encoding proteins with PHD finger, FN Ⅲ and VID domains, which are typical for VIL proteins. Cluster analysis of VILs proteins showes different evolutionary branches exist in grasses and arabidopsis. VIN3 play key roles in Arabidopsis during vernalization memory, however, whose homologs do not exist in the graminaceous plants. In Brachypodium distachyon, there are three protein, Bd VIL2, 4, and 5, closer to VRN5, another VIN3 family protein in Arabidopsis, which play an important role both in vernalization and photoperiod flowering pathway.(2) Bd VIL2-5 are induced by vernalization in deffernt levels. Between in long day and short day conditions, the expression of Bd VIL2, 3 has no significant difference, while Bd VIL4 was expressed higher in the long-day condition and Bd VIL5 enriches in the short day condition. Bd VIL4 was preferentially expressed in young tissues spatially, while Bd VIL5 expressed in various parts of the plant with only slightly superiority in the stem and the apex.(3) Bd VIL4 RNA interference does not affect the response to photoperiod and vernalization with undifferentiated flowering time. After day 25℃/ night 13℃ treatment, Bd VIL4 RNAi plants flower significantly late accompanied with downregulated SPLs and Bd FTLs. The results show that Bd VIL4 with Bd VIL5 are reduced by the relatively higher temprature(25℃) and enriched in lower temprature(13 ℃), and mi R156 accumulated at lower temperature in contrast. Therefore, Bd VIL4 and Bd VIL5 are involved in the ambient temprature response passway. While mi R156 are upregulated in both Bd VIL4 and Bd VIL5 RNAi plants,it is concluded that Bd VIL4 and Bd VIL5, with partially redundant function, indirectly upregulated the expression of SPL genes through inhibiting mi R156, then Bd FTL1 and Bd FTL2 reduced consequently.Bd VIL4 RNA interference allows spikes with increased branches, even occasionally with secondary branches, which is in accord with the function of SPLs.