The leaf is an important photosynthetic organ and plays an essential role in the growth and development of plants. Leaf color mutants are ideal materials for studying chlorophyll metabolism, chloroplast development, and photosynthesis. In this study, we identified an EMS-induced mutant, yl2.1, which exhibited yellow cotyledons and true leaves that did not turn green with leaf growth. The yl2.1 locus was controlled by a recessive nuclear gene. The CsYL2.1 was mapped to a 166.7-kb genomic region on chromosome 2, which contains 24 predicted genes. Only one non-synonymous single nucleotide polymorphism (SNP) was found between yl2.1 and wt-WD1 that was located in Exon 7 of Csa2G263900, resulting in an amino acid substitution. CsYL2.1 encodes a plastid isoform of triose phosphate isomerase (pdTPI), which catalyzes the reversible conversion of dihydroxyacetone phosphate (DHAP) to glyceraldehyde-3-phosphate (GAP) in chloroplasts. CsYL2.1 was highly expressed in the cotyledons and leaves. The mesophyll cells of the yl2.1 leaves contained reduced chlorophyll and abnormal chloroplasts. Correspondingly, the photosynthetic efficiency of the yl2.1 leaves was impaired. Identification of CsYL2.1 is helpful in elucidating the function of ptTPI in the chlorophyll metabolism and chloroplast development and understanding the molecular mechanism of this leaf color variant in cucumber.

TCP proteins are plant-specific transcription factors widely implicated in leaf morphogenesis and senescence, flowering, lateral branching, hormone crosstalk, and stress responses. However, the relationship between the transcription pattern of TCPs and organ development in cucumber has not been systematically studied. In this study, we performed a genome-wide identification of putative TCP genes and analyzed their chromosomal location, gene structure, conserved motif, and transcript expression. A total of 27 putative TCP genes were identified and characterized in cucumber. All 27 putative CsTCP genes were classified into class I and class II. Class I comprised 12 CsTCPs and Class II contained 15 CsTCPs. The 27 putative CsTCP genes were randomly distributed in five of seven chromosomes in cucumber. Four putative CsTCP genes were found to contain putative miR319 target sites. Quantitative RT-PCR revealed that 27 putative CsTCP genes exhibited different expression patterns in cucumber tissues and floral organ development. Transcript expression and phenotype analysis showed that the putative CsTCP genes responded to temperature and photoperiod and were induced by gibberellin (GA)and ethylene treatment, which suggested that CsTCP genes may regulate the lateral branching by involving in multiple signal pathways. These results lay the foundation for studying the function of cucumber TCP genes in the future.

Trichomes that cover the epidermis of aerial plant organs play multiple roles in plant protection. Compared with a unicellular trichome in model plants, the development mechanism of the multicellular trichome is largely unclear. Notably, variations in trichome development are often accompanied by defects in the biosynthesis of cuticle and secondary metabolites; however, major questions about the interactions between developmental differences in trichomes and defects in metabolic pathways remain unanswered. Here, we characterized the glabrous mutantmict/csgl1/cstbhvia combined metabolomic and transcriptomic analyses to extend our limited knowledge regarding multicellular trichome development and metabolism in cucumber.Mictwas found to be explicitly expressed within trichome cells. Transcriptomic analysis indicated that genes involved in flavonoid and cuticle metabolism are significantly downregulated inmictmutants. Further metabolomic analysis confirmed that flavonoids, lipids, and cuticle compositions are dramatically altered inmictmutants. Additional studies revealed thatMictregulates flavonoid, lipid, and cuticle biosynthesis by likely directly binding to downstream functional genes, such asCsTT4,CsFLS1,CsCER26, andCsMYB36. These findings suggest that specific metabolic pathways (e.g., flavonoids and cuticle components) are co-regulated byMictand provide insights into transcriptional regulation mechanisms of multicellular trichome development and its specific metabolism in cucumber.

Background: Trichomes are excellent model systems for the analysis of cell differentiation and play essential roles in plant protection. From cucumber inbred line ‘WD1’, we identified an EMS-induced trichome abnormally developing mutant,nps, which exhibited smaller, denser and no pyramid-shaped head trichomes.Results: Using F₂and BC₁populations constructed from a cross betweennpsand ‘9930’, the genetic analysis showed that thenpstrait is controlled by a single recessive nuclear gene. We identifiedCsNpsby map-based cloning with 576 individuals of the F₂population generated from the cross ofnpsand inbred line ‘9930’. TheCsNpswas located at a 13.4-kb genomic region on chromosome 3, which region contains three predicted genes. Sequence analysis showed that only one single nucleotide mutation (C → T) between 9930 andnpswas found in the second exon ofCsa3G748220, a plant-specific class I HD-Zip gene. The result of allelism test also indicated thatnpsis a novel allelic mutant ofMict(Micro-trichome). Thus,npswas renamedmict-L130F. By comparing the transcriptome ofmict-L130Fvs WD1 and 06–2 (mict) vs 06–1 (wildtype, near-isogenic line of 06–2), several potential target genes that may be related to trichome development were identified.Conclusions: Our results demonstrate thatMict-L130Fis involved in the morphogenesis of trichomes. Map-based cloning of theMict-L130Fgene could promote the study of trichome development in cucumber.