Transcriptional regulation of functional genes involved in cuticular wax biosynthesis by MYB family transcriptional factors in plants
Abstract
MYB transcription factor family is one of the largest families in the plant kingdom, specifically characterized by a Helix -turn-helix domain in their structural configurati on with two repeats of R2R3 MYB domain and are known for regulating plant stress tolerance (abiotic and biotic) through ABA dependent signaling systems. R2R3 - MYB family transcription factors plays a role in the regulation of specific downstream genes of V ery Long Chain Fatty Acid Biosynthesis like KCS1, KCS2, KCS6 and KCR1, related to water use efficiency traits like cuticular wax biosynthesis. Analysis of R2R3 - MYB family transcription factors regulating the production of cuticular wax emphasizes the value of the family outside of traditionally accepted roles in stress tolerance. Some MYB transcription factors like MYB96, MYB94, MYB41, MYB30, MYB106 and MYB16 isolated from Arabidopsis thaliana (Col -0) are studied with respect to their role in biosynthesis o f cuticular waxes under environmental stress signals. In the present review we intensely focused on the elucidation of R2R3 - MYB family transcription factors MYB96, MYB94, MYB41, MYB30, MYB106 and MYB16 role in cuticular wax biosynthesis and aid in the dev elopment of transgenics for enhanced stress tolerance.
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Introduction
The cuticle framework is provided by cutin, a plant specific lipophylic, insoluble polyester consists of C16 and C18 hydroxy and epoxy-hydroxy fatty acids and glycerol monomers [1] [2] [3] that covers the surface of aerial plant parts and protects plants from nonstomatal water loss [4], pathogen infection [5], insect attack [6] , and UV radiation [7] [8]. Cuticle is lined as intracuticular waxes and overlaid with epicuticular waxes, which consist mainly of very-long-chain fatty acids (VLCFAs; C20 to C34) and their derivatives, such as alcohols, aldehydes, alkanes, ketones, and wax esters [9] [10] [11]. The recent studies strongly support that cuticular wax accumulation is closely associated with drought resistance responses [12] [13] [14] [15].
The above figure is deduced from internet showing the pathway of cuticular wax biosytnesis.
Wax bio-synthesis in plants starts with fatty acid synthesis in the plastid (de novo synthesis of C16 and C18) and elongation takes place in endoplasmic reticulum (C20–C34) with the help of four distinct enzymes 3-ketoacyl-CoA synthase (KCS), 3ketoacyl-CoA reductase (KCR), 3-hydroxacyl-CoA dehydratese (HCD), trans-2,3-enoyl-CoA reductase (ECR). But the chain length and substrate specificity of the condensation reaction, a rate limiting step and the subsequent elongated products alkanes, aldehydes, primary alcohols, secondary alcohols, ketones and wax esters is determined by the KCS enzyme [16].
Several transcription factors are involved in cuticular wax biosynthesis like WAX INDUCER1 (WIN1)/SHINE1 (SHN1), SHN2 or SHN3 and its phylogenetic neighbours in the AP2/ERF family [12] [17] [14], homeodomain-leucine zipper (HDZIP) group IV transcription factors [18], OUTER CELL LAYER1 from maize (Zea mays)[19]. Some MYB family transcription factors [20] [21] [22] [23] [24] regulate the genes involved in biosynthesis and transport of cuticlar components. In the present review we focus on the functions of R2R3- MYB family transcription factors in relation to cuticular wax biosynthesis.
Conclusion
In the past, most studies have been focused on MYB transcription factors in plant defense against abiotic and biotic stresses; however, its role in regulating cuticular wax biosynthesis is not clearly understood. As MYB transcription factors are essential to plant -specialized metab olism, understanding their functions in cuticular wax biosynthesis will provide ways to successfully reengineer crop plants to produce higher yield. MYB transcription factors like MYB96, MYB94, MYB41, MYB30, MYB106, and MYB16 were studied in respect of the ir role in Bio -synthesis of cuticular waxes under environmental stress signals. Elucidating how MYBs regulate cuticular wax biosynthesis metabolism is critical not only for improving crop stress tolerance but also for increasing the productivity of crop pl ants. Individual expression of ATMYB96, ATMYB94, ATMYB41, ATMYB30, ATMYB106, and ATMYB16 imparted stress tolerance, by accumulating cuticular wax. But an attempt to overexpress any one of the MYB TF here MYB96, directly involved in the expression of downst ream genes of Very Long Chain Fatty Acid Biosynthesis like KCS1, KCS2, KCS6 and KCR1 along with one key enzyme like KCS would be a potential option for engineering crops plants and develop transgenics for improved stress tolerance.