[This corrects the article DOI: 10.3389/fpls.2022.875011.].
Iron-deficiency chlorosis is a common nutritional disorder in crops grown on alkaline or calcareous soils. Although the acclimation mechanism to iron deficiency has been investigated, the genetic regulation of iron acquisition is still unclear. Here, by comparing the iron uptake process between the iron-poor-soil-tolerant citrus species Zhique (ZQ) and the iron-poor-soil-sensitive citrus species trifoliate orange (TO), we discovered that enhanced root H + efflux is crucial for the tolerance to iron deficiency in ZQ. The H+ efflux is mainly regulated by a plasma membrane-localized H+-ATPase, HA6, the expression of which is upregulated in plants grown in soil with low iron content, and significantly higher in the roots of ZQ than TO. Overexpression of the HA6 gene in the Arabidopsis thaliana aha2 mutant, defective in iron uptake, recovered the wild-type phenotype. In parallel, overexpression of the HA6 gene in TO significantly increased iron content of plants. Moreover, an iron deficiency-induced transcription factor, MYB308, was revealed to bind the promoter and activate the expression of HA6 in ZQ in yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays. Overexpression of MYB308 in ZQ roots significantly increased the expression level of the HA6 gene. However, MYB308 cannot bind or activate the HA6 promoter in TO due to the sequence variation of the corresponding MYB308 binding motif. Taking these results together, we propose that the MYB308 could activate HA6 to promote root H+ efflux and iron uptake, and that the distinctive MYB308-HA6 transcriptional module may be, at least in part, responsible for the iron deficiency tolerance in citrus.
Polyploidy varieties have been reported to exhibit higher stress tolerance relative to their diploid relatives, however, the underlying molecular and physiological mechanisms remain poorly understood. In this study, a batch of autotetraploid Citrus wilsonii were identified from a natural seedling population, and these tetraploid seedlings exhibited greater tolerance to drought stress than their diploids siblings. A global transcriptome analysis revealed that a large number of genes involved in photosynthesis response were enriched in tetraploids under drought stress, which was consistent with the changes in photosynthetic indices including Pn, gs, Tr, Ci, and chlorophyll contents. Compared with diploids, phosphorylation was also modified in the tetraploids after drought stress, as detected through tandem mass tag (TMT)-labeled proteomics. Additionally, tetraploids prioritized the regulation of plant hormone signal transduction at the transcriptional level after drought stress, which was also demonstrated by increased levels of IAA, ABA, and SA and reduced levels of GA3 and JA. Collectively, our results confirmed that the synergistic regulation of photosynthesis response, phosphorylation modification and plant hormone signaling resulted in drought tolerance of autotetraploid C. wilsonii germplasm.
Citrus junos is a widely used citrus grafting rootstock in china because of its excellent tolerance to cold stress. However, the physiological and molecular mechanisms underlying this process remain unknown. In this study, physiological and tandem mass tag-based proteomic analyses were performed to elucidate the mechanism of the Citrus junos response to cold stress. Physiological data showed that severe cold stress decreased photosynthetic parameters and caused cell membrane damage and membrane lipid peroxidation in Citrus junos leaves compared to the control. A total of 6, 678 distinct proteins species were identified, and 413 proteins species were significantly differentially accumulated in the leaves of Citrus junos seedling after cold stress. Bioinformatics analysis revealed that the differentially abundance protein species mainly related to the starch and sucrose metabolism, secondary metabolites biosynthesis and phenylpropanoid biosynthesis in the leaves of Citrus junos seedling after cold stress. Further physiological assays showed that the contents of soluble starch, fructose, glucose and phenols were significantly increased in Citrus junos leaves after cold stress. Collectively, our data reveals that sugar and secondary metabolism could play important roles in Citrus junos in response to cold stress.
Citrus , China , Cold-Shock Response , Plant Proteins , Proteomics , Secondary Metabolism , Stress, Physiological , Sugars
Target spot, a recently observed citrus disease that is caused by Pseudofabraea citricarpa, can cause substantial economic losses in citrus production. In this study, a 797 bp marker specific to Ps. citricarpa was identified via random amplified polymorphic DNA (RAPD) technique. The primer pair Pc-SFP/Pc-SRP, which was designed from RAPD amplicons, was utilized as a sequence-characterized amplified region (SCAR) marker. This marker identified Ps. citricarpa with a single and distinct band of 389 bp but did not amplify DNA from other tested fungal species. The PCR assay was highly sensitive to the target DNA at picogram levels and could reliably amplify Ps. citricarpa sequences with the Pc-SFP/Pc-SRP primer pair. The SCAR marker that was identified in the present study can facilitate rapid decision-making and precise disease forecasting and management.
Plant Diseases/microbiology , Random Amplified Polymorphic DNA Technique , Citrus/microbiology , DNA Primers , DNA, Fungal/analysis , Polymerase Chain Reaction , Sequence Analysis, DNA
Defoliation, dieback and mortality of Satsuma mandarin (Citrus unshiu), as well as kumquat (Fortunella margarita), in Chenggu County, Shaanxi Province, China was first noticed in 2006 and caused substantial economic losses to citrus production. The incidence of leaves infected approached 100% in some badly infected orchards. The disease prevailed only in late winter and early spring, where early symptoms were rounded and target-like spots on leaves. The disease was named target spot. Black conidiomata were observed on the upper surface of the leaves. A Cryptosporiopsis species was consistently recovered from the infected leaves, shoots, and branches. Koch's postulates were fulfilled by inoculating the conidial suspension of Cryptosporiopsis sp. onto the leaves of Satsuma mandarin. Phylogenetic analysis based on LSU sequence data indicated that this taxon clustered in Cryptosporiopsis (teleomorph: Neofabraea, Dermateaceae). Phylogenetic analysis based on ITS, SSU, and TUB indicated that the isolates of Cryptosporiopsis sp. constituted a distinct clade. Further study also demonstrated that this taxon was morphologically distinct from other species of Cryptosporiopsis, thus suggesting it might belong to an undescribed species. The name Cryptosporiopsis citricarpa sp. nov. is given to accommodate the fungal pathogen in this study.
