4-methylumbelliferone (4-MU) enhances drought tolerance of apple by regulating rhizosphere microbial diversity and root architecture

The dwarfing rootstocks-mediated high-density apple orchard is becoming the main practice management.Currently,dwarfing rootstocks are widely used worldwide,but their shallow root system and drought sensitivity necessitate high irrigation requirements.Here,the root transcriptome and metabolome of dwarfing(M9-T337,a drought-sensitive rootstock)and vigorous rootstocks(Malus sieversii,a drought-tolerant species,is commonly used as a rootstock)showed that a coumarin derivative,4-Methylumbelliferon(4-MU),was found to accumulate significantly in the roots of vigorous rootstock under drought condition.When exogenous 4-MU was applied to the roots of dwarfing rootstock under drought treatment,the plants displayed increased root biomass,higher root-to-shoot ratio,greater photosynthesis,and elevated water use efficiency.In addition,diversity and structure analysis of the rhizosphere soil microbial community demonstrated that 4-MU treatment increased the relative abundance of putatively beneficial bacteria and fungi.Of these,Pseudomonas,Bacillus,Streptomyces,and Chryseolinea bacterial strains and Acremonium,Trichoderma,and Phoma fungal strains known for root growth,or systemic resistance against drought stress,were significantly accumulated in the roots of dwarfing rootstock after 4-MU treatment under drought stress condition.Taken together,we identified a promising compound—4-MU,as a useful tool,to strengthen the drought tolerance of apple dwarfing rootstock.

The GAMYB-like gene SlMYB33 mediates flowering and pollen development in tomato

GAMYBs are positive GA signaling factors that exhibit essential functions in reproductive development,particularly in anther and pollen development.However,there is no direct evidence of the regulation of any GAMYB in these biological processes in tomato(Solanum lycopersicum).Here,we identified a tomato GAMYB-like gene,SlMYB33,and characterized its specific roles.SlMYB33 is predominately expressed in the stamens and pistils.During flower development,high mRNA abundance of SlMYB33 is detected in both male and female organs,such as microspore mother cells,anthers,pollen grains,and ovules.Silencing of SlMYB33 leads to delayed flowering,aberrant pollen viability,and poor fertility in tomato.Histological analyses indicate that SlMYB33 exerts its function in pollen development in the mature stage.Further transcriptomic analyses imply that the knockdown of SlMYB33 significantly inhibits the expression of genes related to flowering in shoot apices,and alters the transcription of genes controlling sugar metabolism in anthers.Taken together,our study suggests that SlMYB33 regulates tomato flowering and pollen maturity,probably by modulating the expression of genes responsible for flowering and sugar metabolism,respectively.

The tomato 2-oxoglutarate-dependent dioxygenase gene SlF3HL is critical for chilling stress tolerance

Low temperature is a major stress that severely affects plant development,growth,distribution,and productivity.Here,we examined the function of a 2-oxoglutarate-dependent dioxygenase-encoding gene,SlF3HL,in chilling stress responses in tomato(Solanum lycopersicum cv.Alisa Craig[AC]).Knockdown(KD)of SlF3HL(through RNA interference)in tomato led to increased sensitivity to chilling stress as indicated by elevated levels of electrolyte leakage,malondialdehyde(MDA)and reactive oxygen species(ROS).In addition,the KD plants had decreased levels of proline and decreased activities of peroxisome and superoxide dismutase.The expression of four cold-responsive genes was substantially reduced in the KD plants.Furthermore,seedling growth was significantly greater in AC or SlF3HLoverexpression plants than in the KD plants under either normal growth conditions with methyl jasmonate(MeJA)or chilling stress conditions.SlF3HL appears to positively regulate JA accumulation and the expression of JA biosynthetic and signaling genes under chilling stress.Together,these results suggest that SlF3HL is a positive regulator of chilling stress tolerance and functions in the chilling stress tolerance pathways,possibly by regulating JA biosynthesis,JA signaling,and ROS levels.

Genome editing for plant research and crop improvement

The advent of clustered regularly interspaced short palindromic repeat(CRISPR) has had a profound impact on plant biology, and crop improvement. In this review, we summarize the state-of-the-art development of CRISPR technologies and their applications in plants, from the initial introduction of random small indel(insertion or deletion) mutations at target genomic loci to precision editing such as base editing, prime editing and gene targeting. We describe advances in the use of class 2, types II, V, and VI systems for gene disruption as well as for precise sequence alterations, gene transcription, and epigenome control.

Genetic analysis implicates a molecular chaperone complex in regulating epigenetic silencing of methylated genomic regions

DNA cytosine methylation confers stable epigenetic silencing in plants and many animals.However,the mechanisms underlying DNA methylation-mediated genomic silencing are not fully understood.We conducted a forward genetic screen for cellular factors required for the silencing of a heavily methylated p35S:NPTII transgene in the Arabidopsis thaliana rdm1-1 mutant background,which led to the identification of a Hsp20 family protein,RDS1(rdm1-1 suppressor 1).Loss-of-function mutations in RDS1 released the silencing of the p35S::NPTII transgene in rdm1-1 mutant plants,without changing the DNA methylation state of the transgene.Protein interaction analyses suggest that RDS1 exists in a protein complex consisting of the methyl-DNA binding domain proteins MBD5 and MBD6,two other Hsp20 family proteins,RDS2 and IDM3,a Hsp40/DNAJ family protein,and a Hsp70 family protein.Like rds1 mutations,mutations in RDS2,MBD5,or MBD6 release the silencing of the transgene in the rdm1 mutant background.Our results suggest that Hsp20,Hsp40,and Hsp70 proteins may form a complex that is recruited to some genomic regions with DNA methylation by methyl-DNA binding proteins to regulate the state of silencing of these regions.