Pitaya HpWRKY3 Is Associated with Fruit Sugar Accumulation by Transcriptionally Modulating Sucrose Metabolic Genes HpINV2 and HpSuSy1

Abstract

Sugar level is an important determinant of fruit taste and consumer preferences. However, upstream regulators that control sugar accumulation during fruit maturation are poorly understood. In the present work, we found that glucose is the main sugar in mature pitaya (Hylocereus) fruit, followed by fructose and sucrose. Expression levels of two sucrose-hydrolyzing enzyme genes HpINV2 and HpSuSy1 obviously increased during fruit maturation, which were correlated well with the elevated accumulation of glucose and fructose. A WRKY transcription factor HpWRKY3 was further identified as the putative binding protein of the HpINV2 and HpSuSy1 promoters by yeast one-hybrid and gel mobility shift assays. HpWRKY3 was localized exclusively in the nucleus and possessed trans-activation ability. HpWRKY3 exhibited the similar expression pattern with HpINV2 and HpSuSy1. Finally, transient expression assays in tobacco leaves showed that HpWRKY3 activated the expressions of HpINV2 and HpSuSy1. Taken together, we propose that HpWRKY3 is associated with pitaya fruit sugar accumulation by activating the transcriptions of sucrose metabolic genes. Our findings thus shed light on the transcriptional mechanism that regulates the sugar accumulation during pitaya fruit quality formation.

Activation of the Transcription of BrGA20ox3 by a BrTCP21 Transcription Factor Is Associated with Gibberellin-Delayed Leaf Senescence in Chinese Flowering Cabbage during Storage

“…Overnight cultures of Agrobacteria were collected by centrifugation, resuspended in MES buffer to 0.8–1.0 OD 600 , incubated at room temperature for 2 h before infiltration. Agrobacteria suspension in a 1-mL syringe (without the metal needle) was carefully press-infiltrated manually onto healthy leaves of 4-week-old Nicotiana benthamiana as described previously [49]. After 2 days of infiltration, the GFP fluorescent signals in the epidermal cells of leaves were directly observed and images were captured by using a Zeiss fluorescence microscope.…”

Transcription Factor OpWRKY3 Is Involved in the Development and Biosynthesis of Camptothecin and Its Precursors in Ophiorrhiza pumila Hairy Roots

“…Knockout of the AtWRKY41 mutant significantly downregulated abscisic acid insensitive 3 (ABI3) and influenced the seed dormancy, through binding to three adjacent W-boxes in the promoter of the ABI3 [31]. Hylocereus polyrhizus WRKY3 ( HpWRKY3 ) was associated with sugar accumulation of pitaya fruit by activating the transcriptions of sucrose metabolic genes [32]. In another study, overexpression of Salvia miltiorrhiza WRKY1 ( SmWRKY1 ) increased five-fold the tanshinone production in transgenic lines through binding to the W-box elements of the promoter 1-deoxy- d -xylulose-5-phosphate reductoisomerase ( SmDXR ) involved in the methylerythritol phosphate (MEP) pathway [33].…”

BrTCP7 Transcription Factor Is Associated with MeJA-Promoted Leaf Senescence by Activating the Expression of BrOPR3 and BrRCCR

“…Overnight cultures of Agrobacteria were collected by centrifugation, resuspended in MES buffer to 0.8–1.0 OD 600 , incubated at room temperature for 2 h before infiltration. Agrobacteria suspension collected in a 1-mL syringe (without the metal needle) was carefully press-infiltrated manually onto healthy leaves of 4-week-old Nicotiana benthamiana as described previously [45]. Two days after infiltration, the GFP fluorescent signals in the epidermal cells of leaves were directly observed and images were captured by using a Zeiss fluorescence microscope (Carl Zeiss AG, Oberkochen, Germany).…”

“…To investigate the transcriptional ability of BrTCP7 in vivo, its full length was inserted into pBD [45] to construct pBD-BrTCP7 as an effector. The positive control (pBD-VP16) was constructed by fusing VP16, a herpes simplex virus-encoded transcriptional activator, to pBD.…”

“…pBD itself was used as a negative control. The GAL4 plasmid with the firefly luciferase ( LUC ) gene was used as a reporter [45], and the renilla luciferase ( REN ) gene in the same plasmid was used as an internal control.…”