The MRE11–ATM–SOG1 DNA damage signaling pathway confers rice immunity to Xanthomonas oryzae

Plants are constantly exposed to microbial pathogens in the environment.One branch of innate plant immunity is mediated by cell-membrane-localized receptors,but less is known about associations between DNA damage and plant immune responses.Here,we show that rice(Oryza sativa)mesophyll cells are prone to DNA double-stranded breaks(DSBs)in response to ZJ173,a strain of Xanthomonas oryzae pv.oryzae(Xoo).The DSB signal transducer ataxia telangiectasia mutated(ATM),but not the ATM and Rad3-related branch,confers resistance against Xoo.Mechanistically,the MRE11–ATM module phosphorylates suppressor of gamma response 1(SOG1),which activates several phenylpropanoid pathway genes and prompts downstream phytoalexin biosynthesis during Xoo infection.Intriguingly,overexpression of the topoisomerase gene TOP6A3 causes a switch from the classic non-homologous end joining(NHEJ)pathway to the alternative NHEJ and homologous recombination pathways atXoo-induced DSBs.The enhanced ATM signaling of the alternative NHEJ pathway strengthens the SOG1-regulated phenylpropanoid pathway and thereby boosts Xoo-induced phytoalexin biosynthesis in TOP6A3-OE1 overexpression lines.Overall,the MRE11–ATM–SOG1 pathway serves as a prime example of plant–pathogen interactions that occur via host non-specific recognition.The function of TOP6-facilitated ATM signaling in the defense response makes it a promising target for breeding of rice germplasm that exhibits resistance to bacterial blight disease without a growth penalty.

Translational control of SOG1 expression in response to replication stress in Arabidopsis

DNA damage,which may arise from cellular activities or be induced by genotoxic stresses,can cause genome instability and significantly affect plant growth and productivity.In response to genotoxic stresses,plants activate the cellular DNA damage response(DDR)to sense the stresses and activate downstream processes.The transcription factor SUPPRESSOR OF GAMMA RESPONSE 1(SOG1),a functional counterpart of mammalian p53,is a master regulator of the DDR in plants.It is activated by various types of DNA lesions and can activate the transcription of hundreds of genes to trigger downstream processes,including cell cycle arrest,DNA repair,endoreplication,and apoptosis.Since SOG1 plays a crucial role in DDR,the activity of SOG1 must be tightly regulated.A recent study published in Plant Cell(Chen et al.,Plant Cell koad126,2023)reports a novel mechanism by which the ATR-WEE1 kinase module promotes SOG1 translation to fine-tune replication stress response.

Roles of MEM1 in safeguarding Arabidopsis genome against DNA damage, inhibiting ATM/SOG1-mediated DNA damage response,and antagonizing global DNA hypermethylation

Arabidopsis methylation elevated mutant 1(mem1)mutants have elevated levels of global DNA methylation. In this study, such mutant alleles showed increased sensitivity to methyl methanesulfonate(MMS). In mem1 mutants, an assortment of genes engaged in DNA damage response(DDR), especially DNA-repair-associated genes, were largely upregulated without MMS treatment, suggestive of activation of the DDR pathway in them. Following MMS treatment, expression levels of multiple DNArepair-associated genes in mem1 mutants were generally lower than in Col-0 plants, whichaccounted for the MMS-sensitive phenotype of the mem1 mutants. A group of DNA methylation pathway genes were upregulated in mem1 mutants under non-MMS-treated conditions, causing elevated global DNA methylation, especially in RNAdirected DNA methylation(Rd DM)-targeted regions.Moreover, MEM1 seemed to help ATAXIATELANGIECTASIA MUTATED(ATM) and/or SUPPRESSOR OF GAMMA RESPONSE 1(SOG1) to fully activate/suppress transcription of a subset of genes regulated simultaneously by MEM1 and ATM and/or SOG1, because expression of such genes decreased/increased consistently in mem1 and atm and/or sog1 mutants, but the decreases/increases in the mem1 mutants were not as dramatic as in the atm and/or sog1 mutants. Thus, our studies reveals roles of MEM1 in safeguarding genome, and interrelationships among DNA damage, activation of DDR, DNA methylation/demethylation, and DNA repair.

方列管型射流式O_2(~1Δ)发生器的COIL出光研究

方列管型射流式 O2 ( 1 Δ)发生器是一种新型高效的氧碘化学激光器 ( COIL)化学能源供给装置。描述了采用该发生器在 COIL上所做的一系列出光实验 ,这些实验着重于考察该发生器的性能参数及相应的 COIL化学效率。结果在 Cl2 流量为 0 .2 5mol/ s、无冷阱、稳定腔条件下获得化学效率高达2 6%。

Distinctive and complementary roles of E2F transcription factors during plant replication stress responses

Survival of living organisms is fully dependent on their maintenance of genome integrity,being permanently threatened by replication stress in proliferating cells.Although the plant DNA damage response(DDR)regulator SOG1 has been demonstrated to cope with replication defects,accumulating evidence points to other pathways functioning independent of SOG1.Here,we report the roles of the Arabidopsis E2FA and EF2B transcription factors,two well-characterized regulators of DNA replication,in plant response to replication stress.Through a combination of reverse genetics and chromatin immunoprecipitation approaches,we show that E2FA and E2FB share many target genes with SOG1,providing evidence for their involvement in the DDR.Analysis of double-and triple-mutant combinations revealed that E2FB,rather than E2FA,plays the most prominent role in sustaining plant growth in the presence of replication defects,either operating antagonistically or synergistically with SOG1.Conversely,SOG1 aids in overcoming the replication defects of E2FA/E2FB-deficient plants.Collectively,our data reveal a complex transcriptional network controlling the replication stress response in which E2Fs and SOG1 act as key regulatory factors.