Transcriptional and phytohormone regulatory network involved in LITTLELEAF-mediated organ size development in cucumber (Cucumis sativus)

Authors: XU, NANA - Henan Agricultural University; FANG, XIAOXIA - Henan Agricultural University; XIE, KUIXI - Henan Agricultural University; CHENG, SIYUAN - Henan Agricultural University; WANG, YUELING - Henan Agricultural University; YANG, SENG - Henan Agricultural University; ZHU, HUAYU - Henan Agricultural University; SUN, SHOURU - Henan Agricultural University; Weng, Yiqun; YANG, LUMING - Henan Agricultural University

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2023
Publication Date: 6/27/2023
Citation: Xu, N., Fang, X., Xie, K., Cheng, S., Wang, Y., Yang, S., Zhu, H., Sun, S., Weng, Y., Yang, L. 2023. Transcriptional and phytohormone regulatory network involved in LITTLELEAF-mediated organ size development in cucumber (Cucumis sativus). Scientia Horticulturae. 321 (2023) 112294. https://doi.org/10.1016/j.scienta.2023.112294.
DOI: https://doi.org/10.1016/j.scienta.2023.112294

Interpretive Summary: Background Organ size, especially fruit size, is an economically important trait in many horticulture crops like cucumber that affects both fruit yield and quality. Organ size determination is the outcome of complex interplays of many factors such as transcription regulators, phytohormones and the environments. The cucumber littleleaf mutant exhibits small organ size, which encodes a defective WD40 repeat domain-containing protein, but the regulatory mechanisms of LL-dependent organ size control are largely unknown. Major findings To test the functions of the ll gene in different genetic backgrounds and explore its regulatory network, we developed near isogenic lines (NILs) by introgressing the recessive mutant form of this gene allele into a Chinese Long cucumber line 9930 with marker assisted selection. Both foreground and background selections were practiced which allowed development of a NIL (ll-NIL) that had >96% genetic composition with 9930 but carried the mutant form of the gene. Comparative morphological analysis between the NILs indicated that the mutant allele for reduced organ size was also manifested in the NIL indicating the effects were independent of the genetic background. Transcriptome profiling using RNA-Seq in the unpollinated ovaries of the two NILs identified differentially expressed genes which were highly enriched with genes known to regulate organ size, as well as transcription factors, and genes in various phytohormone biosynthesis/signaling pathways. RNA-Seq and phytohormone assays found that auxin and cytokinin played more important roles in LL-regulated fruit growth. Who cares These results will be helpful for further explore the molecular mechanism of organ size control in cucumber fruit development.

Technical Abstract: Organ size, especially fruit size, is an economically important trait in many horticulture crops like cucumber (Cucumis sativus L.) which affects both fruit yield and quality. Organ size determination is the outcome of complex interplays of many factors such as transcription regulators, phytohormones and the environments. The cucumber littleleaf (ll) mutation exhibits small organ size, which encodes a defective WD40 repeat domain-containing protein, but the regulatory mechanisms of LL-dependent organ size control are largely unknown. To test the functions of the ll gene in different genetic backgrounds and explore its regulatory network, we developed near isogenic lines (NIL) of ll gene by introgressing the recessive allele into a Chinese Long inbred line 9930 with marker assisted selection (MAS). Both foreground and background selections were practiced which allowed development of a NIL (ll-NIL) at BC2F2 that were homologous at the ll locus and captured >96% genetic background of the recurrent parent. Comparative morphological analysis between the NILs indicated that the mutant allele for reduced organ size was independent of the genetic background. Transcriptome profiling using RNA-Seq in the unpollinated ovaries of the two NILs identified differentially expressed genes which were highly enriched with genes known to regulate organ size, as well as transcription factors, and genes in various phytohormone biosynthesis/signaling pathways. RNA-Seq and phytohormone assays found that auxin and cytokinin played more important roles in LL-regulated fruit growth. These results will be helpful for further explore the molecular mechanism of organ size control in cucumber fruit development.