A mutation in class III homeodomain-leucine zipper (HD-ZIP III) transcription factor results in curly leaf (cl) in cucumber (Cucumis sativus L.)

Authors: RONG, FX - Northwest Agricultural University; CHEN, FF - Northwest Agricultural University; HUNAG, L - Northwest Agricultural University; ZHANG, JY - Northwest Agricultural University; CHENG, ZH - Northwest Agricultural University; HOU, D - Northwest Agricultural University; Weng, Yiqun; CHEN, P - Northwest Agricultural University; LI, YH - Northwest Agricultural University

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2018
Publication Date: 10/17/2018
Citation: Rong, F., Chen, F., Hunag, L., Zhang, J., Cheng, Z., Hou, D., Weng, Y., Chen, P., Li, Y. 2018. A mutation in class III homeodomain-leucine zipper (HD-ZIP III) transcription factor results in curly leaf (cl) in cucumber (Cucumis sativus L.). Journal of Theoretical and Applied Genetics. 132:113-123.

Interpretive Summary: The leaf morphology, including shape and size, is a critical factor influencing plant success and agricultural productivity. For example, moderate leaf rolling generally leads to a more erect plant architecture; this is beneficial for enhancing canopy light capture and reducing transpiration water loss, and increase the photosynthetic efficiency and resistance on environmental stress. Although a number of genes controlling rolled leaf have been identified from rice and other plant species, none have been identified or mapped in cucumber. In this study, we identified and characterized two curly leaf (cl) mutants in cucumber. With map-based cloning, we show that the two mutants are caused by mutations single nucleotide polymorphism (SNPs) at different locations of the same cucumber gene (CsPHB). The CsPHB gene encodes a class III homeodomain-leucine zipper (HD-ZIP III) transcription factor. We further found that the SNPs in the two mutants are both located in miR165/166 complementary sites of the CsPHB gene. Consistent with this, the expression level of CsPHB and miRNA165/166 genes show opposite trends in multiple organs of the mutant/166. This is the first report to clone and characterize the CsPHB gene in the family Cucurbitaceae. The results support CsPHB as an important player in the modulation of leaf shape development in cucumber. While the results are of interest to plant molecular biologists in understanding basic biology of leaf organogenesis in cucurbit crops, cucumber breeders may also be interested in using this trait to possibly improve productivity.

Technical Abstract: Leaf rolling is an important agronomic trait in crop breeding. Moderate leaf rolling minimizes shadowing between leaves, leading to improved photosynthetic efficiency. Although a number of genes controlling rolled leaf have been identified from rice and other plant species, none have been identified or mapped in cucurbit crops. In this study, we identified and characterized two curly leaf (cl) mutants, cl-1 and cl-2 in cucumber. With map-based cloning, we show that cl-1 and cl-2 are allelic mutations and CsPHB (Csa6G525430) was the candidate gene for both mutants. The CsPHB gene encoded a class III homeodomain-leucine zipper (HD-ZIP III) transcription factor. A single non-synonymous mutation in the 4th and 5th exons of the CsPHB was responsible for the cl-1 and cl-2 mutant phenotypes, respectively. The single nucleotide substations in cl-1 and cl-2 were both located in csmiR165/166 complementary sites of CsPHB. The expression level of CsPHB gene in multiple organs of cl-1 mutant was higher than that in the wildtype, while the expression of miRNA165/166 in the two genotypes showed the opposite trend. We speculate that disruption of the binding between the mutant allele of CsPHB and csmiRNA165/166 leads to the curly leaf phenotype. This is the first report to clone and characterize the CsPHB gene in the family Cucurbitaceae. Taken together, these results support CsPHB as an important player in the modulation of leaf shape development in cucumber.