Heterologous Expression of Panax ginseng PgTIP1 Confers Enhanced Salt Tolerance of Soybean Cotyledon Hairy Roots, Composite, and Whole Plants

Abstract

The Panax ginseng TIP gene PgTIP1 was previously demonstrated to have high water channel activity by its heterologous expression in Xenopus laevis oocytes and in yeast; it also plays a significant role in growth of PgTIP1-transgenic Arabidopsis plants under favorable conditions and has enhanced tolerance toward salt and drought treatment. In this work, we first investigated the physiological effects of heterologous PgTIP1 expression in soybean cotyledon hairy roots or composite plants mediated by Agrobacterium rhizogenes toward enhanced salt tolerance. The PgTIP1-transgenic soybean plants mediated by the pollen tube pathway, represented by the lines N and J11, were analyzed at the physiological and molecular levels for enhanced salt tolerance. The results showed that in terms of root-specific heterologous expression, the PgTIP1-transformed soybean cotyledon hairy roots or composite plants displayed superior salt tolerance compared to the empty vector-transformed ones according to the mitigatory effects of hairy root growth reduction, drop in leaf RWC, and rise in REL under salt stress. Additionally, declines in K+ content, increases in Na+ content and Na+/K+ ratios in the hairy roots, stems, or leaves were effectively alleviated by PgTIP1-transformation, particularly the stems and leaves of composite soybean plants. At the whole plant level, PgTIP1-trasgenic soybean lines were found to possess stronger root vigor, reduced root and leaf cell membrane damage, increased SOD, POD, CAT, and APX activities, steadily increased leaf Tr, RWC, and Pn values, and smaller declines in chlorophyll and carotenoid content when exposed to salt stress compared to wild type. Moreover, the distribution patterns of Na+, K+, and Cl- in the roots, stems, and leaves of salt-stressed transgenic plants were readjusted, in that the absorbed Na+ and Cl- were mainly restricted to the roots to reduce their transport to the shoots, and the transport of root-absorbed K+ to the shoots was simultaneously promoted. PgTIP1 transformation into soybean plants enhanced the expression of some stress-related genes (GmPOD, GmAPX1, GmSOS1, and GmCLC1) in the roots and leaves under salt treatment. This indicates that the causes of enhanced salt tolerance of heterologous PgTIP1-transformed soybean are associated with the positive regulation on water relations, ion homeostasis, and ROS scavenging under salt stress both at root-specific and whole plant levels.

Genome-wide characterization and analysis of bHLH transcription factors in Panax ginseng

“…The basic helix-loop-helix (bHLH) transcription factor family, which was named after their highly conserved bHLH domain, is one of the largest transcription factor families found in eukaryotic organisms 8 . These transcription factors are involved in a myriad of regulatory processes, including neurogenesis, myogenesis, and heart development modulation in animals 9 , 10 ; phosphate uptake and glycolysis adjustment in yeast 11 ; and secondary metabolism, epidermal differentiation, and environmental factor response regulation in plants 12 , 13 , 14 , 15 . Typically, a bHLH domain consists of approximately 60 amino acids comprising a stretch of approximately 15 basic amino acids at the N-terminus, followed by two regions of hydrophobic residues predicted to form amphipathic helices separated by an intervening loop 16 .…”

Overexpression of Peroxidase Gene GsPRX9 Confers Salt Tolerance in Soybean

“…Therefore, soybean hairy roots can be used to further verify the gene functions in salt tolerance. In a previous study, PgTIP1 overexpressing soybean hairy roots displayed superior salt tolerance compared to the empty-vector-transformed ones [36]. In this study, we employed soybean hairy roots to investigate the role of GsPRX9 in salt tolerance (Figure 5 and Figure S2).…”

Hairy Root Transformation: A Useful Tool to Explore Gene Function and Expression in Salix spp. Recalcitrant to Transformation

“…sRNAs, peptides and metabolites) between roots and aerial components of the plant. Transgenic hairy roots and composite plant systems can be used to study resistance against different biotic (Mellor et al, 2012; Xue et al, 2017) and abiotic stresses (Kajikawa et al, 2010; An et al, 2017; Du et al, 2018; Li et al, 2019), mycorrhizal associations, and root symbioses (Clemow et al, 2011; Indrasumunar et al, 2015;Billault-Penneteau et al, 2019). Furthermore, the use of the CRISPR/Cas9 technology with hairy root transformation has emerged as an efficient tool for plant genome editing and gene functional studies (Ron et al, 2014; Wang et al, 2016;Du et al, 2018), thus opening a whole new range of applications for Salix spp., such as the manipulation of target biosynthetic pathways through multiplexed genome editing.…”