The HD-ZIP IV transcription factor Tril regulates fruit spine density through gene dosage effects in cucumber

Abstract

Trichomes and fruit spines are important traits that directly affect the appearance quality and commercial value of cucumber. Tril (Trichome-less), an HD-Zip IV transcription factor, plays a crucial role in the initiation of trichomes and fruit spines, but little is known about their exact regulatory mechanisms. In this study, tissue expression pattern analysis indicated that Tril is expressed and functions in the early stage of organ initiation and development. Expression of the Tril gene under the control of its own promoter (the TrilPro::Tril-3*flag fragment) could partly rescue the mutant phenotypes of tril, csgl3 (cucumber glabrous 3, an allelic mutant of tril) and fs1 (few spines 1, a fragment substitution in the Tril promoter region), providing further evidence that Tril is responsible for the initiation of trichomes and fruit spines. In dense spine-type lines, fs1-type lines and different background transgenic lines containing the TrilPro::Tril-3*flag foreign fragment, fruit spine number increased along with the increase in Tril expression, indicating that Tril has a gene dosage effect on fruit spine density in cucumber. The Numerous Spines (NS) gene is a negative regulatory factor of fruit spine density. Characterization of the molecular and genetic interaction between Tril and NS/ns demonstrated that Tril functions upstream of the negative regulator NS with respect to fruit spine initiation. Overall, our results uncover a novel mechanism governing the effect of the Tril gene in regulating fruit spine development and provide a reference for future work on the quality breeding of cucumber.

Phytohormone-Based Regulation of Trichome Development

“…HDZIP transcription factors play key roles in trichome development. AtGL2 in Arabidopsis ( Szymanski et al, 1998 ), SIWo in tomato ( Yang et al, 2011 ), AaHD1 and AaHD8 in A. annua ( Yan et al, 2017 , 2018 ), and CsTril in cucumber ( Du et al, 2020 ) are HDZIP transcription factors that modulate trichome development.…”

“…The GLABRA 1 (GL1)-GLABRA 3 (GL3)/ENHANCER OF GLABRA 3 (EGL3)-TRANSPARENT TESTA GLABRA 1 (TTG1) trichome development complex has been well studied ( Zhao et al, 2008 ); however, knowledge of the interaction between this complex and phytohormones is limited. Sweet wormwood ( Artemisia annua ), tomato ( Solanum lycopersicum ), and cucumber ( Cucumis sativus ) are the main plant species used as models for studying glandular trichome development ( Lv et al, 2017 ; Du et al, 2020 ; Xiong et al, 2020 ), and many studies have indicated that trichome development involves phytohormones ( Yan et al, 2017 ; Chen et al, 2020 ; Yuan et al, 2021 ).…”

A SNP of HD-ZIP I transcription factor leads to distortion of trichome morphology in cucumber (Cucumis sativus L.)

“…Different with mict-L130F mutants, in F 1 progeny, there only single copy of mict-L130F and the expression level of the gene may be affected. It has been reported that Tril has a gene dosage effect on fruit spine density [35]. Thus, we speculated that whether there is also a gene dosage effect existing in Mict and further research are needed.…”

“…Quantitative PCR (qPCR) was conducted using FastStart Universal SYBR Green Master Mix (ROX) (Roche) with a CFX96 Touch™ Real-Time PCR System. The cucumber CsActin gene was selected as an internal control [35]. Three biological replicates were used per gene.…”

A SNP Mutation in Homeodomain-DDT (HD-DDT) Transcription Factor Results in Multiple Trichomes (mt) in Cucumber (Cucumis sativus L.)

“…The mutation of the HD-ZIP IV transcription factor gene Tril (CsaV3_6G049180) could induce the occurrence of two other glabrous mutants (csgl3, tril) in cucumber [23,28,29]. Transgenic expression of the Tril gene could partly rescue the mutant phenotypes of tril, csgl3 and fs1 (few spines 1) [30]. The transformation of the TTG1 gene (Csa4Gm097650, WD-Repeat protein), the GA20ox1 gene (CsaV3_5G005560, gibberellin oxidase), the CsMYB6 gene (Csa009688, MYB transcription factor) and the CsTRY (Csa015371) gene in cucumber showed that all these genes could affect the development of trichomes [25,31,32].…”