Transcriptomic and genetic approaches reveal an essential role of the NAC transcription factor SlNAP1 in the growth and defense response of tomato

With global climate change,plants are frequently being exposed to various stresses,such as pathogen attack,drought,and extreme temperatures.Transcription factors(TFs)play crucial roles in numerous plant biological processes;however,the functions of many tomato(Solanum lycopersicum L.)TFs that regulate plant responses to multiple stresses are largely unknown.Here,using an RNA-seq approach,we identified SlNAP1,a NAC TF-encoding gene,which was strongly induced by various stresses.By generating SlNAP1 transgenic lines and evaluating their responses to biotic and abiotic stresses in tomato,we found that SlNAP1-overexpressing plants showed significantly enhanced defense against two widespread bacterial diseases,leaf speck disease,caused by Pseudomonas syringae pv.tomato(Pst)DC3000,and root-borne bacterial wilt disease,caused by Ralstonia solanacearum.In addition,SlNAP1 overexpression dramatically improved drought tolerance in tomato.Although the SlNAP1-overexpressing plants were shorter than the wild-type plants during the early vegetative stage,eventually,their fruit yield increased by 10.7%.Analysis of different hormone contents revealed a reduced level of physiologically active gibberellins(GAs)and an increased level of salicylic acid(SA)and abscisic acid(ABA)in the SlNAP1-overexpressing plants.Moreover,EMSAs and ChIP-qPCR assays showed that SlNAP1 directly activated the transcription of multiple genes involved in GA deactivation and both SA and ABA biosynthesis.Our findings reveal that SlNAP1 is a positive regulator of the tomato defense response against multiple stresses and thus may be a potential breeding target for improving crop yield and stress resistance.

Mitochondrial retrograde regulation tuning fork in nuclear genes expressions of higher plants

In plant cells, there are three organelles: the nucleus, chloroplast, and mitochondria that store genetic information. The nucleus possesses the majority of genetic information and controls most aspects of organelles gene expression, growth, and development. In return, organelles also send signals back to regulate nuclear gene expression, a process defined as retrograde regulation. The best studies of organelles to nucleus retrograde regulation exist in plant chloroplast-to-nuclear regulation and yeast mitochondria-to-nuclear regulation. In this review, we summarize the recent understanding of mitochondrial retrograde regulation in higher plant, which involves multiple potential signaling pathway in relation to cytoplasmic male-sterility, biotic stress, and abiotic stress. With respect to mitochondrial retrograde regulation signal pathways involved in cytoplasmic male-sterility, we consider that nuclear transcriptional factor genes are the targeted genes regulated by mitochondria to determine the abnormal reproductive development, and the MAPK signaling pathway may be involved in this regulation in Brassica juncea. When plants suffer biotic and abiotic stress, plant cells will initiate cell death or other events directed toward recovering from stress. During this process, we propose that mitochondria may determine how plant cell responds to a given stress through retrograde regulation. Meanwhile, several transducer molecules have also been discussed here. In particular, the Paepe research group reported that leaf mitochondrial modulated whole cell redox homeostasis, set antioxidant capacity, and determined stress resistance through altered signaling and diurnal regulation, which is an indication of plant mitochondria with more active function than ever.

Strigolactones positively regulate abscisic acid-dependent heat and cold tolerance in tomato

Strigolactones are carotenoid-derived phytohormones that impact plant growth and development in diverse ways.However,the roles of strigolactones in the responses to temperature stresses are largely unknown.Here,we demonstrated that strigolactone biosynthesis is induced in tomato(Solanum lycopersicum)by heat and cold stresses.Compromised strigolactone biosynthesis or signaling negatively affected heat and cold tolerance,while application of the synthetic strigolactone analog GR245DS enhanced heat and cold tolerance.Strigolactone-mediated heat and cold tolerance was associated with the induction of abscisic acid(ABA),heat shock protein 70(HSP70)accumulation,C-REPEAT BINDING FACTOR 1(CBF1)transcription,and antioxidant enzyme activity.Importantly,a deficiency in ABA biosynthesis compromised the GR245DS effects on heat and cold stresses and abolished the GR245DS-induced transcription of HSP70,CBF1,and antioxidant-related genes.These results support that strigolactones positively regulate tomato heat and cold tolerance and that they do so at least partially by the induction of CBFs and HSPs and the antioxidant response in an ABA-dependent manner.

Brassinosteroid signaling positively regulates abscisic acid biosynthesis in response to chilling stress in tomato

Brassinosteroids(BRs)and abscisic acid(ABA)are essential regulators of plant growth and stress tolerance.Although the antagonistic interaction of BRs and ABA is proposed to ensure the balance between growth and defense in model plants,the crosstalk between BRs and ABA in response to chilling in tomato(Solanum lycopersicum),a warmclimate horticultural crop,is unclear.Here,we determined that overexpression of the BR biosynthesis gene DWARF(DWF)or the key BR signaling gene BRASSINAZOLE-RESISTANT1(BZR1)increases ABA levels in response to chilling stress via positively regulating the expression of the ABA biosynthesis gene 9-CIS-EPOXYCAROTENOID DIOXYGENASE1(NCED1).BR-induced chilling tolerance was mostly dependent on ABA biosynthesis.Chilling stress or high BR levels decreased the abundance of BRASSINOSTEROID-INSENSITIVE2(BIN2),a negative regulator of BR signaling.Moreover,we observed that chilling stress increases BR levels and results in the accumulation of BZR1.BIN2negatively regulated both the accumulation of BZR1protein and chilling tolerance by suppressing ABA biosynthesis.Our results demonstrate that BR signaling positively regulates chilling tolerance via ABA biosynthesis in tomato.The study has implications in production of warm-climate crops in horticulture.

The critical role of autophagy in plant responses to abiotic stresses

Autophagy is an evolutionary conserved recycling process in eukaryotes whereby intracellular components are engulfed by autophagosomes, which are subsequently transferred to the vacuoles for further degradation and reuse. In organisms like yeast and metazoans, autophagy is actively engaged during environmental perturbation either by degrading denatured proteins and organelles or by interfacing with stress related signaling molecules. Studies over the last decade have also revealed numerous important mechanisms where autophagy is widely involved in plant abiotic stress responses. Autophagy serves as a pivotal route for nutrient remobilization by the degradation of superfluous or damaged cellular cytoplasmic material and organelles. It is also reported to regulate the accumulation of reactive oxygen species, to maintain the cellular redox balance of plants under stressful conditions. Furthermore, autophagy is essential in regulating cellular toxicity by removing aggregated and/or denatured proteins and thereby improving plant stress tolerance. In this review, recent advances in our understanding of autophagy, along with pathways and regulatory networks through which it influences many aspects of plant growth and development in response to nutrient starvation, oxidative stress, osmotic stress and extreme temperatures are discussed.

CHARACTERISTICS OF HERBIVORY/WOUND-ELICITED ELECTRICAL SIGNAL TRANSDUCTION IN TOMATO

Electrical signals commonly occur in plants in response to various environmental changes and have a dominant function in plant acclimation.The transduction of wound-elicited electrical signals in the model plant spedes Arabidopsis has been characterized but the characteristics of electrical signal transduction in response to herbivory or wounding in crop species remain unknown.Here,the features of electrical signals elicited by insect herbivory and wounding in tomato were investigated.Unlike those in Arabidopsis,wounding tomato leaves did not cause leaf-to-leaf electrical signal transduction.In contrast,electrical signals elicited in response to petiole wounding were stronger and more strongly transduced.Leaflet wounding also activated electrical signal transduction and jasmonic acid(JA)signaling within the whole compound leaf.It was also demonstrated that tomato glutamate receptor-like 3.3(GLR3.3)and GLR3.5 mediated leaflet-to-leaflet electrical signal transduction.Herbivory-induced JA accumulation and Helicoverpa armigera resistance were reduced in glr3.3/3.5 plants.This work reveals the nature of electrical signal transduction in tomato and emphasizes the key roles of GLR3.3 and GLR3.5 in electrical signal transduction and JA signaling activation.

HIGHLIGHTS OF THE SPECIAL ISSUE ON"HORTICULTURE RESEARCH FOR GREEN AND SUSTAINABLE DEVELOPMENT"

Horticulture is the science and technology of intensively cultivating plants for food,comfort and beautification purposes.Horticulture comprises a wide range of plants and crops including fruit and nut trees,vegetables,edible fungi,and ornamental plants,as well as tea plants also categorized as horticultural crops in some countries including China.Horticultural products are of great value and serve as important dietary sources of antioxidants,vitamins and mineral nutrients for human nutrition and health.Development of a green and sustainable horticulture,producing more and safer fruit and vegetables,is a prerequisite for meeting the ever-increasing demand of the growing human population.

The MYC2-PUB22-JAZ4 module plays a crucial role in jasmonate signaling in tomato

Jasmonates(JAs),a class of lipid-derived stress hormones,play a crucial role across an array of plant physiological processes and stress responses.Although JA signaling is thought to rely predominantly on the degradation of specific JAZ proteins by SCF^(COI1),it remains unclear whether other pathways are involved in the regulation of JAZ protein stability.Here,we report that PUB22,a plant U-box type E3 ubiquitin ligase,plays a critical role in the regulation of plant resistance against Helicoverpa armigera and other JA responses in tomato.Whereas COI1 physically interacts with JAZ1/2/5/7,PUB22 physically interacts with JAZ1/3/4/6.PUB22 ubiquitinates JAZ4 to promote its degradation via the 26S proteasome pathway.Importantly,we observed that pub22 mutants showreduced resistance to H.armigera,whereas jaz4 single mutants and jaz1 jaz3 jaz4 jaz6 quadruple mutants have enhanced resistance.The hypersensitivity of pub22 mutants to herbivores could be partially rescued by JAZ4 mutation.Moreover,we found that expression of PUB22 can be transcriptionally activated by MYC2,thus forming a positive feedback circuit in JA signaling.We noticed that the PUB22-JAZ4 module also regulates other JA responses,including defense against B.cinerea,inhibition of root elongation,and anthocyanin accumulation.Taken together,these results indicate that PUB22 plays a crucial role in plant growth and defense responses,together with COI1-regulated JA signaling,by targeting specific JAZs.