Slow development restores the fertility of photoperiod-sensitive male-sterile plant lines

Slow development has been shown to be a general mechanism to restore the fertility of thermo-sensitive and photoperiod-sensitive genic male sterile (TGMS and PGMS) lines in Arabidopsis. rpg1 is a TGMS line defective in primexine, which is essential for pollen wall pattern formation. Here, we showed that RPG1-GFP was highly expressed in microsporocytes, microspores, and pollen grains but not in the tapetum in the complemented transgenic line, suggesting that microsporocytes are the main sporophytic cells for primexine formation. Further cytological observations showed that primexine formation in rpg1 was partially restored under slow growth conditions, leading to its fertility restoration. RPG2 is the homolog of RPG1 in Arabidopsis. We revealed that the fertility recovery of rpg1 rpg2 was significantly reduced compared with that of rpg1 under low temperature. The RPG2-GFP protein was also expressed in microsporocytes in the RPG2-GFP (WT) transgenic line. These results suggest that RPG2 plays a redundant role in rpg1 fertility restoration. rpg1 plants were male sterile at the early growth stage, while their fertility was partially restored at the late developmental stage. The fertility of the rpg1 lateral branches was also partially restored. Further growth analysis showed that slow growth at the late reproductive stage or on the lateral branches led to fertility restoration. This work reveals the importance of gene redundancy in fertility restoration for TGMS lines and provides further insight into pollen wall pattern formation.

The skipper Polytremis theca species complex is widely distributed in the south of the Qinling Mountains in China. A recent study of the Polytremis genus suggested that this species might encompass two differentiated lineages. We tested this hypothesis, by carrying out a phylogenetic study of this agricultural pest based on nationwide sampling and the evaluation of mitochondrial and nuclear DNA markers. We show that this species is actually an amalgamation of two sibling taxa (P. t. theca and P. t. fukia), which displayed levels of genetic divergence as great as those generally found between sister species in the Polytremis genus, suggesting that they actually correspond to two distinct species. The Divergence time estimates suggest that an active period of speciation within Polytremis occurred within the Pleistocene eras. Based on its distinct phylogenetic placement and geographical isolation, we suggest that the subspecies should be elevated to full species status under the phylogenetic species concept, which has significant management implications.

Epigenetic modifications are essential for plant development. EFD encodes a SAM-dependent methyltransferase essential for the pollen wall pattern formation and male fertility in Arabidopsis. Here, we found that the expression of DRM2, a de novo DNA methyltransferase in plants, can complement the defects of efd, suggesting its de novo DNA methyltransferase ability. Genetic analysis reveals that EFD plays roles through HB21 as its knockout fully restored the efd fertility. The methylation and H3K27me3 analysis indicates that EFD represses the transcription expression of HB21 through epigenetic modifications. Besides, both EMSA and tobacco transient expression assays showed that HB21 repressed the expression of the genes including CalS5, RPG1/SWEET8, CYP703A2 and NST2 which are essential for pollen formation and anther dehiscence. Altogether, our study reveals a double negative regulatory cascade mediated by epigenetic modifications to coordinate anther development, which provides new insights into epigenetic regulation and anther development.