Promoter variation in a homeobox gene, CpDll, is associated with deeply lobed leaf in Cucurbita pepo L

Authors: BO, KAILIANG - Chinese Academy Of Agricultural Sciences; DUAN, YING - Chinese Academy Of Agricultural Sciences; QIU, XINYAN - Chinese Academy Of Agricultural Sciences; ZHANG, MENG - Chinese Academy Of Agricultural Sciences; SHU, QIN - Chinese Academy Of Agricultural Sciences; SUN, YAPEI - Chinese Academy Of Agricultural Sciences; HE, YADI - Chinese Academy Of Agricultural Sciences; SHI, YUZI - Chinese Academy Of Agricultural Sciences; Weng, Yiqun; WANG, CHANGLIN - Chinese Academy Of Agricultural Sciences

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2021
Publication Date: 1/5/2022
Citation: Bo, K., Duan, Y., Qiu, X., Zhang, M., Shu, Q., Sun, Y., He, Y., Shi, Y., Weng, Y., Wang, C. 2022. Promoter variation in a homeobox gene, CpDll, is associated with deeply lobed leaf in Cucurbita pepo L. Theoretical and Applied Genetics. 135:1223–1234. https://doi.org/10.1007/s00122-021-04026-3.
DOI: https://doi.org/10.1007/s00122-021-04026-3

Interpretive Summary: Leaf shape is an important horticultural trait in zucchini. Lobed leaves have potential advantages for high-density planting and hybrid production. However, little is known about the molecular basis of lobed leaf formation in this important vegetable crop. Here reported the inheritance and map-based cloning of the deeply lobed leaf (CpDll) gene using populations from the cross between two zucchini inbred lines HS-M2 (lobed leaf) and Jin-GL (normal leaf). We conducted QTL (quantitative trait loci) analysis and fine mapping using recombinant inbred line and F2 plants. We show that lobed leaf shape is controlled by a single gene, CpDll, and this gene encodes a type I HD-Zip transcription factor protein. While we did not find any sequence differences in the coding region of this gene between HS-M2 and Jin-GL, there were wide variation in the promoter region. Expression of the CpDll gene in the leaf base of lobed leaves was much higher than in non-lobed leaves. We compared CpDll gene sequences in nine cucurbit crops including cucumber, melon, watermelon, bottle gourd, and pumpkin/squash, and found that conservation in both structure and function of this gene in regulation of lobed leaf formation. Our work provides new insights into the molecular basis of leaf lobe formation in pumpkin/squash and other cucurbit crops. This work also facilitates marker-assisted selection for leaf shape in zucchini breeding. Cucurbit breeders and researchers may have interest in this work.

Technical Abstract: Leaf shape is an important horticultural trait in zucchini (Cucurbita pepo L.). Lobed leaves have potential advantages for high-density planting and hybrid production. However, little is known about the molecular basis of lobed leaf formation in this important vegetable crop. Here, we conducted QTL analysis and fine mapping of the deeply lobed leaf (CpDll) locus using recombinant inbred line and large F2 populations developed from crosses between the lobed-leaf HS-M2, and non-lobed Jin-GL parental lines. We show that CpDll exhibited an incompletely dominance for the lobed leaf shape in HS-M2. Map-based cloning provided evidence that CpCll encodes a type I homeodomain (HD)- and Leu zipper (Zip) element-containing transcription factor. Sequence analysis between HS-M2 and Jin-GL revealed no sequence variations in the coding sequences, whereas numbers variations were identified in the promoter region between them. DUAL-LUC assays revealed significantly stronger promoter activity in HM-S2 than that in Jin-GL. There was also significantly higher expression of CpDll in the leaf base of lobed leaves of HM-S2 compared with non-lobed leaf Jin-GL. Comparative analysis of CpDll gene homologs in nine cucurbit crop species (family Cucurbitaceae) revealed conservation in both structure and function of this gene in regulation of lobed leaf formation. Our work provides new insights into the molecular basis of leaf lobe formation in pumpkin/squash and other cucurbit crops. This work also facilitates marker-assisted selection for leaf shape in zucchini breeding.