English

Abstract

Plant physiology, morphology and biochemistry are genetically controlled by a large set of genes. Expression of these genes is influenced by a number of factors, internal as well as external, including stage of plant development, diseases, drought, salinity, cold, and many others (Yoshioka et al., 2003; Zhang et al., 2001). Some genes are activated or suppressed by a specific stress factor while, many genes respond to more than one stimulus (Kariola et al., 2006). These genes can be classified, on the basis of their expression patterns and/or their responsiveness to environmental stressors, in different groups viz., responsive to dehydration (RD), cold regulated (COR), cold inducible (KIN), lowtemperature induced (LTI), early responsive to dehydration (ERD), salt overly sensitive (SOS), dehydration-responsive element-binding proteins (DREBs) and many more (Shinozaki and Yamaguchi-Shinozaki, 2007; Mahajan and Tuteja, 2005). Among these genes, ERDs have emerged as a new class or group of genes, identified first time by Kiyosue et al. (1994) in Arabidopsis plants dehydrated for one hour. Some members of the ERD group have been studied such as ERD1 (that encodes a Clp protease regulatory subunit; Nakashima et al., 1997), ERD5 (proline dehydrogenase; Kiyosue et al., 1996), ERD8 (hsp8-1; Takahashi et al., 1992), ERD10 (Group II LEA protein = lti29/lti45; Welin et al., 1995) and ERD15 (Kariola et al., 2006; Alves et al., 2011; Ziaf et al., 2011). Among these ERD genes, ERD15 has been used as a stress responsive gene in various stress experiments (Dunaeva and Adamska, 2001; Park et al., 2009; Li et al., 2010) in Arabidopsis and wheat. Nevertheless, its induction and function has been contradictory (Kariola et al., 2006; Ziaf et al., 2011), which can be due to difference in sequence among the species and/or due to some mutations in the sequence from specific crop. Transcript of several genes is accumulated at a specific stage of plant growth or in specific organs, varying to some extent with their function. Some are under the control of endogenous circadian system and thus affect the physiology and metabolism (Yakir et al., 2007). About 6% genes in Arabidopsis, involved in various functions such as photosynthesis, responses to stresses, sugar metabolism and flowering in response to day-length, fluctuate daily and are controlled by circadian clock (Harmer et al., 2000). Wang and Grumet (2004) reported diurnal pattern for transcript level of Pak. J. Agri. Sci., Vol. 53(1), 27-33; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.3695 http://www.pakjas.com.pk