H2O2 Functions as a Downstream Signal of IAA to Mediate H2S-Induced Chilling Tolerance in Cucumber

Hydrogen sulfide (H2S) plays a crucial role in regulating chilling tolerance. However, the role of hydrogen peroxide (H2O2) and auxin in H2S-induced signal transduction in the chilling stress response of plants was unclear. In this study, 1.0 mM exogenous H2O2 and 75 μM indole-3-acetic acid (IAA) significantly improved the chilling tolerance of cucumber seedlings, as demonstrated by the mild plant chilling injury symptoms, lower chilling injury index (CI), electrolyte leakage (EL), and malondialdehyde content (MDA) as well as higher levels of photosynthesis and cold-responsive genes under chilling stress. IAA-induced chilling tolerance was weakened by N, N′-dimethylthiourea (DMTU, a scavenger of H2O2), but the polar transport inhibitor of IAA (1-naphthylphthalamic acid, NPA) did not affect H2O2-induced mitigation of chilling stress. IAA significantly enhanced endogenous H2O2 synthesis, but H2O2 had minimal effects on endogenous IAA content in cucumber seedlings. In addition, the H2O2 scavenger DMTU, inhibitor of H2O2 synthesis (diphenyleneiodonium chloride, DPI), and IAA polar transport inhibitor NPA reduced H2S-induced chilling tolerance. Sodium hydrosulfide (NaHS) increased H2O2 and IAA levels, flavin monooxygenase (FMO) activity, and respiratory burst oxidase homolog (RBOH1) and FMO-like protein (YUCCA2) mRNA levels in cucumber seedlings. DMTU, DPI, and NPA diminished NaHS-induced H2O2 production, but DMTU and DPI did not affect IAA levels induced by NaHS during chilling stress. Taken together, the present data indicate that H2O2 as a downstream signal of IAA mediates H2S-induced chilling tolerance in cucumber seedlings.

WUSCHEL-related homeobox1 (WOX1) regulates vein patterning and leaf size in Cucumis sativus

In plants, WUSCHEL-related homeobox1 (WOX1) homologs promote lamina mediolateral outgrowth. However, the downstream components linking WOX1 and lamina development remain unclear. In this study, we revealed the roles of WOX1 in palmate leaf expansion in cucumber (Cucumis sativus). A cucumber mango fruit (mf) mutant, resulting from truncation of a WOX1-type protein (CsWOX1), displayed abnormal lamina growth and defects in the development of secondary and smaller veins. CsWOX1 was expressed in the middle mesophyll and leaf margins and rescued defects of the Arabidopsis wox1 prs double mutant. Transcriptomic analysis revealed that genes involved in auxin polar transport and auxin response were highly associated with leaf development. Analysis of the cucumber mf rl (round leaf) double mutant revealed that CsWOX1 functioned in vein development via PINOID (CsPID1)-controlled auxin transport. Overexpression of CsWOX1 in cucumber (CsWOX1-OE) affected vein patterning and produced ‘butterfly-shaped’ leaves. CsWOX1 physically interacted with CsTCP4a, which may account for the abnormal lamina development in the mf mutant line and the smaller leaves in the CsWOX1-OE plants. Our findings demonstrated that CsWOX1 regulates cucumber leaf vein development by modulating auxin polar transport; moreover, CsWOX1 regulates leaf size by controlling CIN-TCP genes.

Comparative transcriptome analysis of hard and tender fruit spines of cucumber to identify genes involved in morphological development of fruit spines

Background: The trichomes of cucumber fruits are also called spines. Cucumber has important commercial value, and its fruit spines represent a classical tissue with which to study the cell division and differentiation mode of multicellular trichomes. Although there have been many studies on the development of unicellular trichomes in model plants, the molecular mechanism of multicellular trichome formation remains elusive. In this study, we used a pair of cucumber materials defined as having hard (Ts, wild type) or tender (ts, mutant) spines in a previous study. The whole developmental process of fruit spines was continuously observed by microscopy and SEM. In an attempt to define the developmental stages of fruit spines, transcriptome profiles at different stages were determined to explore the molecular mechanisms underlying the process of spine development. Results: According to significant phenotypic differences, the developmental process of fruit spines was clearly defined as involving four stages. Comparison of transcriptome profiles showed that 803 and 722 genes were upregulated in the stalk (stage II and stage III) and base (stage IV) developmental stages of fruit spines, respectively. Functional analysis of differentially expressed genes (DEGs) showed that for all developmental stages of fruit spines, lipid metabolism, amino acid metabolism, and signal transduction were the most noticeable pathways. However, during the development of the stalk, genes related to auxin polar transport and HD-ZIP transcription factors were significantly upregulated. bHLH transcription factors and cytoskeleton-related genes were significantly upregulated during the development of the base. In addition, stage III was the key point for differentiating between the wild type and mutant. We detected 628 DEGs between the wild type and mutant at this stage. These DEGs are mainly involved in calcium signaling of the cytoskeleton and auxin polar transport, indicating that the main reason for the disorder of the fruit spine developmental pattern in the mutant was a change in cell polarity caused by blocked intercellular signal transmission.Conclusions: Our study defines in great detail the developmental stages of cucumber fruit spines. At the same time, transcriptome profiles are used to present the gene regulatory networks at different developmental stages of cucumber fruit spines. In addition, we analyzed transcriptomic data of a wild type and mutant to elucidate the biological pathways involving C-type lectin receptor-like kinase that regulate the development of fruit spines.

Characterization of the Auxin Efflux Transporter PIN Proteins in Pear

PIN-FORMED (PIN) encodes a key auxin polar transport family that plays a crucial role in the outward transport of auxin and several growth and development processes, including dwarfing trees. We identified a dwarfing pear rootstock ‘OHF51’ (Pyrus communis), which limits the growth vigor of the ‘Xueqing’ (Pyrus bretschneideri × Pyrus pyrifolia) scion, and isolated 14 putative PbPINs from the pear Pyrus bretschneideri. The phylogenic relationships, structure, promoter regions, and expression patterns were analyzed. PbPINs were classified into two main groups based on the protein domain structure and categorized into three major groups using the neighbor-joining algorithm. Promoter analysis demonstrated that PbPINs might be closely related to plant growth and development. Through quantitative real-time PCR (qRT-PCR) analysis, we found that the expression patterns of 14 PbPINs varied upon exposure to different organs in dwarfing and vigorous stocks, ‘OHF51’ and ‘QN101’ (Pyrus betulifolia), indicating that they might play varying roles in different tissues and participated in the regulation of growth vigor. These results provide fundamental insights into the characteristics and evolution of the PINs family, as well as the possible relationship between dwarfing ability and auxin polar transport.

Going North

When China announced its Belt and Road Initiative (BRI), most of the attention focused on the joint building of transportation infrastructure across the Eurasian landmass and the Indian Ocean. However, with the release of the Arctic Policy in 2018, China incorporated the Arctic shipping lanes into the BRI transport network. Development of shipping in polar waters requires collaboration with Arctic countries. This chapter discusses the challenges China faces in exploring new maritime ways in the Arctic and collaborating with Russia in the development of the Arctic Blue Economic Corridor. The investment projects in the Arctic are considered in the format of eight development zones located in the polar regions along Russian part of the Northern Sea Route. The author concludes that Arctic shipping lanes have a great potential to be efficiently incorporated into the BRI transport network. However, there are many specific technological and economic challenges to be considered and met before polar transport routes may become any viable alternatives to southern maritime routes used by China.