Expression of Arabidopsis SHN1 in Indian Mulberry (Morus indica L.) Increases Leaf Surface Wax Content and Reduces Post-harvest Water Loss.

R S Sajeevan,Karaba N Nataraja,D S Gurumurthy,N Pallavi,M B Shivanna,K S Shivashankara

doi:10.3389/fpls.2017.00418

Abstract

Mulberry (Morus species) leaf is the sole food for monophagous silkworms, Bombyx mori L. Abiotic stresses such as drought, salinity, and high temperature, significantly decrease mulberry productivity and post-harvest water loss from leaves influence silkworm growth and cocoon yield. Leaf surface properties regulate direct water loss through the cuticular layer. Leaf surface waxes, contribute for cuticular resistance and protect mesophyll cells from desiccation. In this study we attempted to overexpress AtSHN1, a transcription factor associated with epicuticular wax biosynthesis to increase leaf surface wax load in mulberry. Agrobacterium mediated in vitro transformation was carried out using hypocotyl and cotyledonary explants of Indian mulberry (cv. M5). Mulberry transgenic plants expressing AtSHN1 displayed dark green shiny appearance with increased leaf surface wax content. Scanning electron microscopy (SEM) and gas chromatograph–mass spectrometry (GC-MS) analysis showed change in pattern of surface wax deposition and significant change in wax composition in AtSHN1 overexpressors. Increased wax content altered leaf surface properties as there was significant difference in water droplet contact angle and diameter between transgenic and wild type plants. The transgenic plants showed significant improvement in leaf moisture retention capacity even 5 h after harvest and there was slow degradation of total buffer soluble protein in detached leaves compared to wild type. Silkworm bioassay did not indicate any undesirable effects on larval growth and cocoon yield. This study demonstrated that expression of AtSHN1, can increase surface wax load and reduce the post-harvest water loss in mulberry.

Highlights

Mulberry, a member of the family Moraceae is commercially cultivated as the sole source of food for monophagous silkworm, Bombyx mori L
Expression of AtSHN1 changed the pattern of epicuticular wax crystals on the adaxial and abaxial leaf surfaces
Compared to adaxial leaf surface, there were fewer wax crystals observed in abaxial surface of mulberry transgenic plants (Figure 4)

Summary

Introduction

A member of the family Moraceae is commercially cultivated as the sole source of food for monophagous silkworm, Bombyx mori L. Increase in mulberry productivity is vital for sericulture industry. To meet the silk demand, there is a need to increase mulberry leaf production. Major mulberry growing areas in India are under dry and irrigated conditions. Under these conditions, abiotic stresses such as drought, salinity, and alkalinity cause 50–60% yield loss (Rao, 2002). Abiotic stresses such as drought, salinity, and alkalinity cause 50–60% yield loss (Rao, 2002) In addition to these constraints, post-harvest water loss due to the time lag between leaf harvest and silkworm feeding influences silkworm growth and cocoon yield (Mamrutha et al, 2010). Slow water loss from harvested leaves is a desirable trait, which helps in maintaining post-harvest leaf quality. The importance of leaf surface wax in regulating leaf moisture loss has been demonstrated and a positive correlation between surface wax load and moisture retention capacity (MRC) has been shown in mulberry (Mamrutha et al, 2010)

Methods

Results

Conclusion