The U6 Biogenesis-Like I Plays an Important Role in Maize Kernel and Seedling Development by Affecting the 3＇ End Processing of U6 snRNA

Regulation of gene expression at the post-transcriptional level is of crucial importance in the development of an organism. Here we present the characterization of a maize gene, U6 biogenesis-like 1 （UBL1）, which plays an important role in kernel and seedling development by influencing pre-mRNA splicing. The ubll mutant, exhibiting small kernel and weak seedling, was isolated from a Mutator-tagged population. Trans- genic complementation and three independent mutant alleles confirmed that UBL1, which encodes a putative RNA exonuclease belonging to the 2H phosphodiesterase superfamily, is responsible for the phenotype of ubll. We demonstrated that UBL1 possess the RNA exonuclease activity in vitro and found that loss of UBL1 function in ubll causes decreased level and abnormal 3＇ end constitution of snRNA U6, resulting in splicing defect of mRNAs. Through the in vitro and in vivo studies replacing two histidines with alanines in the H-X-T/S-X （X is a hydrophobic residue） motifs we demonstrated that these two motifs are essential for the normal function of UBL1. We further showed that the function of UBL1 may be conserved across a wide phylogenetic distance as the heterologous expression of maize UBL1 could complement the Arabidopsis ubll mutant.

Potassium transporter OsHAK9 regulates seed germination under salt stress by preventing gibberellin degradation through mediating OsGA2ox7 in rice

Soil salinity has a major impact on rice seed germination,severely limiting rice production.Herein,a rice germination defective mutant under salt stress(gdss)was identified by using chemical mutagenesis.The GDSS gene was detected via MutMap and shown to encode potassium transporter OsHAK9.Phenotypic analysis of complementation and mutant lines demonstrated that OsHAK9 was an essential regulator responsible for seed germination under salt stress.OsHAK9 is highly expressed in germinating seed embryos.Ion contents and non-invasive micro-test technology results showed that OsHAK9 restricted K^(+)efflux in salt-exposed germinating seeds for the balance of K^(+)/Na^(+).Disruption of OsHAK9 significantly reduced gibberellin 4(GA4)levels,and the germination defective phenotype of oshak9a was partly rescued by exogenous GA_(3)treatment under salt stress.RNA sequencing(RNA-seq)and real-time quantitative polymerase chain reaction analysis demonstrated that the disruption of OsHAK9 improved the GA-deactivated gene OsGA2ox7 expression in germinating seeds under salt stress,and the expression of OsGA2ox7 was significantly inhibited by salt stress.Null mutants of OsGA2ox7 created using clustered,regularly interspaced,short palindromic repeat(CRISPR)/CRISPR-associated nuclease 9 approach displayed a dramatically increased seed germination ability under salt stress.Overall,our results highlight that OsHAK9 regulates seed germination performance under salt stress involving preventing GA degradation by mediating OsGA2ox7,which provides a novel clue about the relationship between GA and OsHAKs in rice.

Aβ-ketoacyl-CoA Synthase OsCUT1 Confers Increased Drought Tolerance in Rice

Drought stress is one of the major environmental factors affecting crop growth and productivity.Cuticular wax plays essential roles in protecting plants from environmental stress via forming a hydrophobic barrier on leaf epidermis.In this study,we analyzed nine members(OsCUT1‒OsCUT9)ofβ-ketoacyl-CoA synthase,the rate-limiting key enzyme for cuticular wax synthesis in rice by homology search and domain prediction.The expression levels of OsCUT genes under different abiotic stresses were investigated and OsCUT1 down-regulated by abiotic stress was selected for further function validation.Compared to the wild type,overexpression of OsCUT1(OX-OsCUT1)exhibited significantly increased drought resistance.Epicuticular wax was increased on the leaf surface of OX-OsCUT1 and the chlorophyll leaching experiment showed that the cuticular permeability was decreased in the OX-OsCUT1 plants.Moreover,overexpression of OsCUT1 didn’t result in the significant changes of major agronomic traits.In total,these results suggested that OsCUT1 is a promising gene for engineering rice plants with enhanced drought tolerance.