Guard-cell-specific expression of Arabidopsis ABF4 improves drought tolerance of tomato and tobacco

Abstract

Abscisic acid (ABA), the hormone associated with seed maturation and stress responses, activates a signal transduction pathway culminating in stomatal closure. Reflecting the central position of this hormone in many plant processes, many genes involved in ABA signaling have been identified. However, biotechnological approaches manipulating these genes in guard cells have rarely been applied to crops with an objective of engineering drought tolerance. We have used the Arabidopsis bZIP transcription factor, ABF4, under the control of guard-cell-specific KST1 promoter for transformation of tobacco and tomato. Expression was shown to be guard-cell-specific, and ABF4-mGFP fusion proteins accumulated in guard cell nuclei. All transgenic lines showed significant increase in drought tolerance when seedlings or mature plants were subjected to prolonged water deficit. These plants exhibited significantly lower water loss per unit leaf area compared to wild type, higher water potential, and relative water contents during water deficit. Importantly, the plants did not develop the severe growth retardation frequently encountered when stress-related transcription factors were expressed constitutively, demonstrating the advantage of tissue- or cell-specific gene manipulations as useful tools to improve plant drought tolerance and also other water-related traits under water-limiting environments.