Drought tolerance

Plants can be subjected to slowly developing water shortages (ie, taking days, weeks, or months), or they may face short-term deficits of water (ie, hours to days). In these situations, plants adapt by responding accordingly, minimizing water loss and maximizing water uptake. Long-term responses • In the above-ground portion of the plant: inhibition of shoot growth, reduced transpiration area, grain abortion, senescence, metabolic acclimation, osmotic adjustment, anthocyanin accumulation, carotenoid degradation, intervention of osmoprotectants, ROS-scavenging enzymes • In the below-ground portion of the plant: turgor maintenance, sustained root growth, increased root/shoot, increased absorption area == Regulatory network of drought tolerance ==

In response to drought conditions, there is an alteration of gene expression, induced by or activated by transcription factors (TFs). These TFs bind to specific cis-elements to induce the expression of targeted stress-inducible genes, allowing for products to be transcribed that help with stress response and tolerance. DREB2 TFs DREB proteins are involved in a variety of functions related to drought tolerance. For example, DREB proteins including DREB2A cooperate with AREB/ABF proteins in gene expression, specifically in the DREB2A gene under osmotic stress conditions. DREB2 also induces the expression of heat-related genes, such as heat shock protein. Overexpression of DREB2Aca enhances drought and heat stress tolerance levels in Arabidopsis. AREB/ABF TFs AREB/ABFs are ABA-responsive bZIP-type TFs which bind to ABA-responsive elements (ABREs) in stress-responsive promoters and activate gene expression. AREB1, AREB2, ABF3, and ABF1 have important roles in ABA signalling in the vegetative stage, as ABA controls the expression of genes associated with drought response and tolerance. The native form of AREB1 cannot target drought stress genes like RD29B in Arabidopsis, so modification is necessary for transcriptional activation. AREB/ABFs are positively regulated by SnRK2s, controlling the activity of target proteins via phosphorylation. This regulation also functions in the control of drought tolerance in the vegetative stage as well as the seed maturation and germination. Other TFs TFs such as NAC (composed of NAM, ATAF, and CUC), are also related to drought response in Arabidopsis and rice. Overexpression in the aforementioned plants improves stress and drought tolerance. They also may be related to root growth and senescence, two physiological traits related to drought tolerance. ==Natural drought tolerance adaptations==

'') is a drought-escaping plant with natural drought tolerance. Some of its natural adaptations include silver-gray hairs that protect against drying; a deep root system; and having seeds that only germinate when conditions are favorable.|391x391px Plants in naturally arid conditions retain large amounts of biomass due to drought tolerance and can be classified into 4 categories of adaptation: • Drought-escaping plants: annuals that germinate and grow only during times of sufficient times of moisture to complete their life cycle. • Drought-evading plants: non-succulent perennials which restrict their growth only to periods of moisture availability. • Drought-enduring plants: also known as xerophytes, these evergreen shrubs have extensive root systems along with morphological and physiological adaptations which enable them to maintain growth even in times of extreme drought conditions. • Drought-resisting plants: also known as succulent perennials, they have water stored in their leaves and stems for sparing uses. Structural adaptations Many adaptations for dry conditions are structural, including the following: • Adaptations of the stomata to reduce water loss, such as reduced numbers, sunken pits, waxy surfaces.... • Reduced number of leaves and their surface area. • Water storage in succulent above-ground parts or water-filled tubers. • Crassulacean acid metabolism (CAM metabolism) allows plants to get carbon dioxide at night and store malic acid during the day, allowing photosynthesis to take place with minimized water loss. • Adaptations in the root system to increase water absorption. • Trichomes (small hairs) on the leaves to absorb atmospheric water. ==Importance for agriculture==

With the frequency and severity of droughts increasing in recent years, damage to crops has become more serious, lowering the crop yield, growth, and production. One such project from CGIAR involves introducing genes such as DREB1 into lowland rice, upland rice, and wheat to evaluate drought tolerance in fields. This project aims to select at least 10 lines for agricultural use. and the Heat and Drought Wheat Improvement Consortium (HeDWIC), a network that facilitates global coordination of wheat research to adapt to a future with more severe weather extremes. Impediments to the agricultural commercialization of drought tolerant plants The development of genetically modified crops includes multiple patents for genes and promoters, such as the marker genes in a vector, as well as transformation techniques. Therefore, freedom-to-operate (FTO) surveys should be implemented in collaborations for developing drought tolerant crops. Large amounts of money are also needed for the development of genetically modified groups. To bring a new genetically modified crop into the commercial market, it has been estimated to cost USD 136 million over 13 years. This poses a problem for development, as only a small number of companies can afford to develop drought-tolerant crops, and it is difficult for research institutions to sustain funding for this period of time. Therefore, a multinational framework with more collaboration among multiple disciples is needed to sustain projects of this size. ==Importance in horticulture==

Plant transformation has been used to develop multiple drought resistant crop varieties, but only limited varieties of ornamental plants. However, abiotic stress resistance is being explored in ornamental plants by Ornamental Biosciences. Transgenic Petunias, Poinsettias, New Guinea Impatiens, and Geraniums are being evaluated for frost, drought, and disease resistance. This will allow for a wider range of environments in which these plants can grow. ==Drought-tolerant plants==

This is a list of selected plant families, species and/or genus that tolerate drought: • Acacia • Adenium • Aeonium • Agapanthus • Agave • Aloe • Angelonia • Anredera cordifolia • Araujia sericifera • Arctotheca calendula • Asphodelus • Asparagus aethiopicus • Banksia • Begonia • Bougainvillea • Buddleja davidii • Bulbine • Cactus • Calibrachoa • Carpobrotus • Cestrum parqui • Cistus albidus • Cosmos • Crassula • Curio • Drosanthemum • Dudleya • Echeveria • Echinacea • Eriogonum • Eucalyptus • Euphorbia milii • Gaillardia • Gazania rigens • Gonialoe • Graptopetalum • Grevillea • Haberlea • Haloxylon ammodendron • Haworthia • Helianthus • Impatiens hawkeri • Ipomoea cairica • Lantana camara • Melaleuca • Mesembryanthemum • Nandina domestica • Nerium oleander • Olea europaea • Pelargonium • Petunia • Portulaca • Portulacaria afra • Ramonda serbica • Ricinus communis • Rosemary • Salvia • Santolina • Sedum • Senecio angulatus • Senecio elegans • Tetradenia riparia • Thunbergia alata • Vinca • Vitis vinifera • Yucca ==See also==