Abstract
Salinity is an environmental stress that causes decline in crop yield. Avicennia officinalis and other mangroves have adaptations such as ultrafiltration at the roots aided by apoplastic cell wall barriers to thrive in saline conditions. We studied a cytochrome P450 gene from A. officinalis, AoCYP94B1, and its putative ortholog in Arabidopsis (Arabidopsis thaliana), AtCYP94B1, which are involved in apoplastic barrier formation. Both genes were induced by 30 min of salt treatment in the roots. Heterologous expression of AoCYP94B1 in the atcyp94b1 Arabidopsis mutant and wild-type rice (Oryza sativa) conferred increased NaCl tolerance to seedlings by enhancing root suberin deposition. Histochemical staining and gas chromatography-tandem mass spectrometry quantification of suberin precursors confirmed the role of CYP94B1 in suberin biosynthesis. Using chromatin immunoprecipitation and yeast one-hybrid and luciferase assays, we identified AtWRKY33 as the upstream regulator of AtCYP94B1 in Arabidopsis. In addition, atwrky33 mutants exhibited reduced suberin and salt-sensitive phenotypes, which were rescued by expressing 35S::AtCYP94B1 in the atwrky33 background. This further confirmed that AtWRKY33-mediated regulation of AtCYP94B1 is part of the salt tolerance mechanism. Our findings may help efforts aimed at generating salt-tolerant crops.
Highlights
Salinity is a major environmental stress factor that leads to reduced crop productivity
We show that heterologous expression of AoCYP94B1 increased the salt tolerance and root suberin deposition in Arabidopsis and rice seedlings
A phylogenetic tree was constructed based on the derived amino acid sequence of AoCYP94B1 with other members of this subfamily (Supplemental Figure S1A)
Summary
Salinity is a major environmental stress factor that leads to reduced crop productivity. The progressive increase in soil salinization exacerbates the already damaging effect of steady reduction in the area of arable land worldwide (Parida and Das, 2005; Agarwal et al, 2014). Na+ is the major toxic ion found in high saline soils, which imparts osmotic as well as ionic stresses. Mangroves have evolved various adaptive strategies to flourish under high saline conditions. One of the important adaptations exhibited by most plants, and to a greater extent by mangroves, is ultrafiltration at the roots by the presence of apoplastic barriers in the roots (Scholander, 1968). We have shown that a salt secretor mangrove, A. officinalis restricts 90-95 % salt at the roots due to the presence of enhanced apoplastic barriers (Krishnamurthy et al, 2014)
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