The CsTM alters multicellular trichome morphology and enhances resistance against aphid by interacting with CsTIP1;1 in cucumber.

The multicellular trichomes of cucumber (Cucumis sativus L.) serve as the primary defense barrier against external factors, whose impact extends beyond plant growth and development to include commercial characteristics of fruits. The aphid (Aphis gossypii Glover) is one of prominent pests in cucumber cultivation. However, the relationship between physical properties of trichomes and the aphid resistance at molecular level remains largely unexplored. Here, a spontaneous mutant trichome morphology (tm) was characterized by increased susceptibility towards aphid. Further observations showed the tm exhibited a higher and narrower trichome base, which was significantly distinguishable from that in wild-type (WT). We conducted map-based cloning and identified the candidate, CsTM, encoding a C-lectin receptor-like kinase. The knockout mutant demonstrated the role of CsTM in trichome morphogenesis. The presence of SNP does not regulate the relative expression of CsTM, but diminishes the CsTM abundance of membrane proteins in tm. Interestingly, CsTM was found to interact with CsTIP1;1, which encodes an aquaporin with extensive reports in plant resistance and growth development. The subsequent aphid resistance experiments revealed that both CsTM and CsTIP1;1 regulated the development of trichomes and conferred resistance against aphid by affecting cytoplasmic H2O2 contents. Transcriptome analysis revealed a significant enrichment of genes associated with pathogenesis, calcium binding and cellulose synthase. Overall, our study elucidates an unidentified mechanism that CsTM-CsTIP1;1 alters multicellular trichome morphology and enhances resistance against aphid, thus providing a wholly new perspective for trichome morphogenesis in cucumber.

Comparative Transcriptome Analysis of Hard and Tender Fruit Spines of Cucumber to Identify Genes Involved in the Morphological Development of Fruit Spines.

The spines of cucumber fruit not only have important commercial value but are also a classical tissue to study cell division and differentiation modes of multicellular trichomes. It has been reported that CsTs (C-type Lectin receptor-like kinase) can influence the development of fruit spines. In this study, we took a pair of cucumber materials defined as hard (Ts, wild type) and tender spines (ts, mutant) and defined the developmental process of fruit spines as consisting of four stages (stage I to stage IV) by continuously observing by microscope and SEM. Comparisons of transcriptome profiles at different development stages of wild-type spines showed that 803 and 722 genes were upregulated in the stalk (stage II and stage III) and base (stage IV) development stages of fruit spines, respectively. The function analysis of DEGs showed that genes related to auxin polar transport and HD-ZIP transcription factor are significantly upregulated during the development of the stalk. bHLH transcription factors and cytoskeleton-related genes were significantly upregulated during the development of the base. In addition, stage III is the key point for the difference between wild-type and mutant spines. We detected 628 DEGs between wild type and mutant at stage III. These DEGs are mainly involved in the calcium signaling of the cytoskeleton and auxin polar transport. Coincidentally, we found that CsVTI11, a factor involved in auxin signal transmission, can interact with CsTs in vivo, but this interaction does not occur between CsVTI11 and Csts, further suggesting that CsTs may regulate the development of fruit spines by influencing cell polarity. These results provide useful tools to study the molecular networks associated with cucumber fruit spine development and elucidate the biological pathways that C-type Lectin receptor-like kinase plays in regulating the development of fruit spines.

A CsTu-TS1 regulatory module promotes fruit tubercule formation in cucumber.

The fruit epidermal features such as the size of tubercules are important fruit quality traits for cucumber production. But the mechanisms underlying tubercule formation remain elusive. Here, tubercule size locus CsTS1 was identified by map-based cloning and was found to encode an oleosin protein. Allelic variation was identified in the promoter region of CsTS1, resulting in low expression of CsTS1 in all 22 different small-warty or nonwarty cucumber lines. High CsTS1 expression levels were closely correlated with increased fruit tubercule size among 44 different cucumber lines. Transgenic complementation and RNAi-mediated gene silencing of CsTS1 in transgenic cucumber plants demonstrated that CsTS1 positively regulates the development of tubercules. CsTS1 is highly expressed in the peel at fruit tubercule forming and enlargement stage. Auxin content and expression of three auxin signalling pathway genes were altered in the 35S:CsTS1 and CsTS1-RNAi fruit tubercules, a result that was supported by comparing the cell size of the control and transgenic fruit tubercules. CsTu, a C2 H2 zinc finger domain transcription factor that regulates tubercule initiation, binds directly to the CsTS1 promoter and promotes its expression. Taken together, our results reveal a novel mechanism in which the CsTu-TS1 complex promotes fruit tubercule formation in cucumber.

Classification of fruit trichomes in cucumber and effects of plant hormones on type II fruit trichome development.

MAIN CONCLUSION: Cucumber fruit trichomes could be classified into eight types; all of them are multicellular with complex and different developmental processes as compared with unicellular trichomes in other plants. The fruit trichomes or fruit spines of cucumber, Cucumis sativus L., are highly specialized structures originating from epidermal cells with diverse morphology, which grow perpendicular to the fruit surface. To understand the underlying molecular mechanisms of fruit trichome development, in this study, we conducted morphological characterization and classification of cucumber fruit trichomes and their developmental processes. We examined the fruit trichomes among 200 cucumber varieties, which could be classified into eight morphologically distinct types (I-VIII). Investigation of the organogenesis of the eight types of trichomes revealed two main developmental patterns. The development of glandular trichomes had multiple stages including initiation and expansion of the trichome precursor cell protuberating out of the epidermal surface, followed by periclinal bipartition to two cells (top and bottom) which later formed the head region and the stalk, respectively, through subsequent cell divisions. The non-glandular trichome development started with the expansion of the precursor cell perpendicularly to the epidermal plane followed by cell periclinal division to form a stalk comprising of some rectangle cells and a pointed apex cell. The base cell then started anticlinal bipartition to two cells, which then underwent many cell divisions to form a multicellular spherical structure. In addition, phytohormones as environmental cues were closely related to trichome development. We found that GA and BAP were capable of increasing trichome number per fruit with distinct effects under different concentrations.