Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 163

BREEDING OBJECTIVES. Different objectives have been proposed for genetic transformation of date palms (Saker, 2011), for gene silencing (Niblett and Bailey, 2012) and for gene editing (Sattar et al., 2017). The primary objectives have been to promote resistance to pests and diseases, especially the red palm weevil (Rhynchophorus ferrugineus) (Soroker and Colazza, 2017) and Bayoud using foreign genes that would confer resistance. Another approach is to induce silencing of the genes in the pest or pathogen that would thereby confer resistance (Niblett and Bailey, 2012). A general view of the potential for genome editing in date palm has been reviewed (Sattar et al., 2017). This approach can be useful to target biotic and abiotic stresses by modifying the expression of key genes involved in resistance to various pests and diseases, by modifying physiological processes involved in growth or flowering or to improve fruit size and quality.

PROTOCOLS AND ACCOMPLISHMENTS. Genetic transformation of date palm has been reported (Saker et al., 2007a, 2009; Saker, 2011; Gambino and Gribaudo, 2012; Mousavi et al., 2014a,b; Aslam et al., 2015; Allam and Saker, 2017; Mousavi et al., 2017). Early studies were involved with transient gene expression in embryogenic cultures. These studies focused on the optimization of technical parameters, i.e. preculture media, particle size and energy and distance of the bombarded tissue, controlling DNA delivery by particle bombardment to date palm embryogenic cultures and somatic embryos (Saker et al., 2007a; Habashi et al., 2008; Mousavi et al., 2009, 2014b). Transformation of shoot tip-derived cultures by Agrobacterium tumefaciens was reported by Mousavi et al. (2014b) and Saker et al. (2009). These studies used β-glucuronidase (GUS) as a reporter gene under the control of a constitutive promoter, i.e. CaMV 35S or rice Act1, and followed analysis of expression by histochemical staining or by PCR to identify the presence of the transgene. Regeneration of transformed plantlets was confirmed. Refined protocols for transformation of embryogenic cultures by particle bombardment, using GUS as a reporter gene were published (Mousavi et al., 2014a; Allam and Saker, 2017; Mousavi et al., 2017). Agrobacterium-mediated transformation of embryogenic cultures of ‘Khalas’ and ‘Medjool’ with Cry1a to transfer resistance to the date palm weevil has been reported (Badr-Elden et al., 2017). The Cry1a gene codes for a bacterial toxin that attacks insects and if expressed in transgenic plants can confer resistance to insects. Another study used the cholesterol oxidase (ChoA) gene, which provides resistance against insect attack; transformation of embryogenic cultures was accomplished by particle bombardment (Allam and Saker, 2017). However, these studies are still at initial stages of tissue culture, and several years are still required prior to testing the resistance of trees. To partially overcome the long timeframe required for maturation and fruit production in transgenic date palms, a different transgenic approach was recently applied for studying gene expression in specific date palm tissues. Following microinjection of date fruits with a binary plasmid-containing GUS under the control of the CaMV 35S promotor, its transient expression was analysed (Solliman, 2017; Solliman et al., 2017). Expression of the gene was observed, suggesting this method could be used for screening of genes and promoters as candidates in date palms.