USING BIOTECHNOLOGY TO IMPROVE RESISTANCE TO ENVIRONMENTAL STRESS IN FRUIT CROPS: THE IMPORTANCE OF UNDERSTANDING PHYSIOLOGY

Abstract

Environmental stress can significantly impact the yield, fruit quality, and longevity of fruit trees. In particular, freeze injury can result in the loss of an entire crop or even an entire orchard. Over the past two decades, significant advances have been made in understanding the genetic regulation of cold hardiness, as well as resistance to other abiotic stresses. At first, research focused on isolating and characterizing cold-regulated (cor) genes and then advanced to the discovery of cold-induced transcription factors and the characterization of cold-induced changes in whole genomes using microarray technologies. Metabolomics, and proteomics have also provided a wealth of new information on the metabolism and biochemistry of cold acclimation. In fruit trees, and woody plants in general, cold hardiness is a complex trait and a thorough understanding of the physiology of freezing tolerance is needed if biotechnology is going to be used effectively to improve environmental stress resistance. The factors that limit cold hardiness in mid-winter are very different from those that are responsible for frost susceptibility in the spring. In contrast to what is observed in herbaceous crops, tissues in woody plants that are in very close proximity to each other can differ dramatically in cold hardiness and the mechanisms by which they cold acclimate. For example, xylem tissues are generally less cold hardy than bark tissues, and the flower buds of some fruit crops exhibit deep supercooling, a freeze-avoidance mechanism that relies on the biophysical properties of the bud tissues. Therefore, different approaches will be needed to influence cold resistance depending on the type of injury (mid-winter or spring) and tissue-type (buds vs. stems) that is being targeted for improvement. Despite this complexity, significant opportunities exist for improving resistance to environmental stress in fruit crops. The targeting of dehydrin proteins to flower buds and the use of transcription factors to regulate suites of genes are two approaches. Additionally, the overexpression of antixodant enzyme (APX or SOD) genes is also a viable approach to improving resistance to several environmental stresses. Recent genomic and proteomic research on stress response in fruit trees is also being used to develop a more comprehensive understanding of environmental stress resistance.