Carrot DcALFIN4 and DcALFIN7 Transcription Factors Boost Carotenoid Levels and Participate Differentially in Salt Stress Tolerance When Expressed in Arabidopsis thaliana and Actinidia deliciosa

Abstract

ALFIN-like transcription factors (ALs) are involved in several physiological processes such as seed germination, root development and abiotic stress responses in plants. In carrot (Daucus carota), the expression of DcPSY2, a gene encoding phytoene synthase required for carotenoid biosynthesis, is induced after salt and abscisic acid (ABA) treatment. Interestingly, the DcPSY2 promoter contains multiple ALFIN response elements. By in silico analysis, we identified two putative genes with the molecular characteristics of ALs, DcAL4 and DcAL7, in the carrot transcriptome. These genes encode nuclear proteins that transactivate reporter genes and bind to the carrot DcPSY2 promoter in yeast. The expression of both genes is induced in carrot under salt stress, especially DcAL4 which also responds to ABA treatment. Transgenic homozygous T3 Arabidopsis thaliana lines that stably express DcAL4 and DcAL7 show a higher survival rate with respect to control plants after chronic salt stress. Of note is that DcAL4 lines present a better performance in salt treatments, correlating with the expression level of DcAL4, AtPSY and AtDXR and an increase in carotenoid and chlorophyll contents. Likewise, DcAL4 transgenic kiwi (Actinidia deliciosa) lines show increased carotenoid and chlorophyll content and higher survival rate compared to control plants after chronic salt treatment. Therefore, DcAL4 and DcAL7 encode functional transcription factors, while ectopic expression of DcAL4 provides increased tolerance to salinity in Arabidopsis and Kiwi plants.

Putative Daucus carota Capsanthin-Capsorubin Synthase (DcCCS) Possesses Lycopene β-Cyclase Activity, Boosts Carotenoid Levels, and Increases Salt Tolerance in Heterologous Plants

“…deliciosa is a salt-sensitive cultivar that leads to decreased vegetative growth, reduced vegetative development, and lower photosynthetic yield when exposed to saline conditions [52,53]. The development of transgenic kiwi plants with increased carotenoids and tolerance to salt stress has been proposed as a useful strategy to overcome this issue [60,61]. Of note, it has been reported that LCYB plays a key role in carotenoid biosynthesis and accumulation in kiwi [62].…”

“…Of note, it has been reported that LCYB plays a key role in carotenoid biosynthesis and accumulation in kiwi [62]. By following the previously published transformation protocol [61], we obtained A. deliciosa-transformed calli that were subjected to chronic NaCl survival assay [62] to preliminarily evaluate the salt tolerance conferred by the ectopic expression of DcLCYB2. Two-month-old transformed calli were placed on a solid half-strength MS medium supplemented with ascending NaCl concentrations, and survival rate was determined at 5 and 15 days of chronic treatment ( Figures 4A,B and S6) by quantification of green living calli or dark dead calli.…”

“…Kiwi plants (Actinidia deliciosa cv. Hayward, CA, USA) were a generous gift from Viverosur Ltd.a (Longitudinal Sur Km 174, Teno 174, Curicó, Chile) and maintained in vitro, as previously reported [61].…”

Transcriptome Analysis of the Salt-Treated Actinidia deliciosa (A. Chev.) C. F. Liang and A. R. Ferguson Plantlets

“…Hence, finding genes or molecular markers related to the traits is vital for fruit tree breeding. Modern techniques, for example, transcriptome, proteomics, and genomics can help screen salt-tolerancerelated genes or molecular markers [2,7,8]. Combining cross-breeding with transcriptome sequencing technology to screen kiwifruit salt-tolerance-related genes is helpful for assisting in the breeding of salt-tolerant varieties [8][9][10].…”

“…Recent studies have shown that kiwifruit, like other salt-intolerant species, exhibit slowed growth, yellowing of leaves, and even death under salt-stressed environmental conditions [11]. The study of tree transcriptomes enables us to obtain new insights into the genetic basis for the formation of tree traits [7,8,10]. The study of salt stress response in plants has become a hot topic, and transcriptomic analysis has identified metabolic pathways associated with salt stress, including plant hormone signal transduction [12], lignin synthesis [13], starch, and the sucrose metabolism pathway [14,15].…”