Sugar is an indispensable source of energy for plant growth and development, and it requires the participation of sugar transporter proteins (STPs) for crossing the hydrophobic barrier in plants.  Here, we systematically identified the genes encoding sugar transporters in the genome of maize (Zea mays L.), analyzed their expression patterns under different conditions, and determined their functions in disease resistance.  The results showed that the mazie sugar transporter family contained 24 members, all of which were predicted to be distributed on the cell membrane and had a highly conserved transmembrane transport domain.  The tissue-specific expression of the maize sugar transporter genes was analyzed, and the expression level of these genes was found to be significantly different in different tissues.  The analysis of biotic and abiotic stress data showed that the expression levels of the sugar transporter genes changed significantly under different stress factors.  The expression levels of ZmSTP2 and ZmSTP20 continued to increase following Fusarium graminearum infection.  By performing disease resistance analysis of zmstp2 and zmstp20 mutants, we found that after inoculation with Cochliobolus carbonum, Setosphaeria turcica, Cochliobolus heterostrophus, and F. graminearum, the lesion area of the mutants was significantly higher than that of the wild-type B73 plant.  In this study, the genes encoding sugar transporters in maize were systematically identified and analyzed at the whole genome level.  The expression patterns of the sugar transporter-encoding genes in different tissues of maize and under biotic and abiotic stresses were revealed, which laid an important theoretical foundation for further elucidation of their functions.

Botrytis cinerea is a typical necrotrophic pathogenic fungus that causes severe diseases in a wide range of plant species, leading to significant economic losses.  Our previous study showed that BcSDR1 positively regulates growth, development, and pathogenicity of B. cinerea.  However, the regulation mechanism of BcSDR1 and the relationship between BcSDR1 and cAMP and MAPK signaling pathways are not well understood.  In this study, transcriptome data showed that BcSDR1 is involved in glucose transmembrane transport, signal transduction, secondary metabolism, and other biological processes.  BcSDR1 mutant (BCt41) showed remarkably weak sensitivity to cAMP and MAPK signaling pathways specific inhibitors, SQ22536 and U0126, and significantly decreased cAMP content.  The key genes of cAMP and MAPK signaling pathways, BcGB1, BcBTP1, BcBOS1, BcRAS1, and BcBMP3 were significantly upregulated, whereas BcPLC1, BcBCG1, BcCDC4, BcSAK1, BcATF1, and BcBAP1 were significantly downregulated (P<0.05).   BcSDR1 was obviously upregulated in BcBCG2, BcBCG3, BcPKA1, and BcPKAR RNA interference (RNAi)  mutants, but significantly downregulated in BcPKA2, BcBMP1, and BcBMP3 RNAi mutants.  Thus, BcBCG2, BcBCG3, BcPKA1, and BcPKAR negatively regulate BcSDR1 expression, whereas BcPKA2, BcBMP1, and BcBMP3 positively regulate BcSDR1 expression.

DNA methylation plays an important role in plant growth and development, and in regulating the activity of transposable elements (TEs).  Research on DNA methylation-related (DMR) genes has been reported in Arabidopsis, but little research on DMR genes has been reported in Brassica rapa and Brassica oleracea, the genomes of which exhibit significant differences in TE content.  In this study, we identified 78 and 77 DMR genes in Brassica rapa and Brassica oleracea, respectively.  Detailed analysis revealed that the numbers of DMR genes in different DMR pathways varied in B. rapa and B. oleracea.  The evolutionary selection pressure of DMR genes in B. rapa and B. oleracea was compared, and the DMR genes showed differential evolution between these two species.  The nucleotide diversity (π) and selective sweep (Tajima’s D) revealed footprints of selection in the B. rapa and B. oleracea populations.  Transcriptome analysis showed that most DMR genes exhibited similar expression characteristics in B. rapa and B. oleracea.  This study dissects the evolutionary differences and genetic variations of the DMR genes in B. rapa and B. oleracea, and will provide valuable resources for future research on the divergent evolution of DNA methylation between B. rapa and B. oleracea.

Whole genome duplication (WGD) and tandem duplication (TD) are important modes of gene amplification and functional innovation, and they are common in plant genome evolution.  We analyzed the genomes of three Solanaceae species (Solanum lycopersicum, Capsicum annuum, and Petunia inflata), which share a common distant ancestor with Vitis vinifera, Theobroma cacao, and Coffea canephora but have undergone an extra whole genome triplication (WGT) event.  The analysis was used to investigate the phenomenon of tandem gene evolution with (S. lycopersicum) or without WGT (V. vinifera).  Among the tandem gene arrays in these genomes, we found that V. vinifera, which has not experienced the WGT event, retained relatively more and larger tandem duplicated gene (TDG) clusters than the Solanaceae species that experienced the WGT event.  Larger TDG clusters tend to be derived from older TD events, so this indicates that continuous TDGs (absolute dosage) accumulated during long-term evolution.  In addition, WGD and TD show a significant bias in the functional categories of the genes retained.  WGD tends to retain dose-sensitive genes related to biological processes, including DNA-binding and transcription factor activity, while TD tends to retain genes involved in stress resistance.  WGD and TD also provide more possibilities for gene functional innovation through gene fusion and fission.  The TDG cluster containing the tomato fusarium wilt resistance gene I3 contains 15 genes, and one of these genes, Solyc07g055560, has undergone a fusion event after the duplication events.  These data provide evidence that helps explain the new functionalization of TDGs in adapting to environmental changes.