A Welcome Message from The Editor

It is with profound pleasure that we write this editorial to welcome you to the new journal, “Pakistan Biomedical Journal” (PBMJ), an interdisciplinary international journal. PBMJ has successfully completed its first volume and now its the second volume. We greatly appreciate the response of scientists who have contributed previously and are still contributing to this new journal. The subject of the journal is interesting and we try to address the health related concerns of public and improve the understandingof scientific phenomenons by researchers. Research discoveries are happening at a fast pace, in all the fields and PBMJ provides an ideal forum for exchange of scientific knowledge in terms of full length papers, surveys, reviews, case studies, letters to editor and systematic analysis. PBMJ is committed to publishing all manuscripts receiving a high recommendation from reviewers. The intention of PBMJ is to create space for generation of new knowledge, debate, collaborations among national and international scientists. Our vision is to promote research that will be helpful for knowledge sharing, new discoveries, development of critical thinking among the upcoming scholars, guidance for policy makers, awareness among the concerned community and ultimately benefitting the general population in improving health and fitness at large. It is a matter of pride for us to haveexcellent editorial board members from renowned institutes. We aim to have the best standards of quality of the published manuscripts. With every issue, we are continuously trying to improve the standards. We look forward for more exciting researches and scientific studies from all over the world. We would like to extend a very warm welcome to the readers of PBMJ and hope you will join us as authors, reviewers and editors in future.

Isolation and Functional Characterization of High Affinity Potassium Transporter Hkt Gene in Yeast and Expression Profiling in Tobacco Nicotiana Tabacum

Alternative splicing is widely observed in animals and plants. Intron retention in transcripts and presence of 5ʹ and 3ʹ splice sites within these introns mediate alternate splicing. This research work was intended to characterize the high affinity potassium transporter (HKT) from barley in model system (tobacco and arabidopsis) and functional complementation in yeast (Saccharomyces cervisceae) heterologous system. Relative expression analysis detected different HvHKT2;1 isoforms in barley (Hordeum vulgare) under both normal and high saline conditions. Besides barley, stable integration of insertions corresponding to two introns, were also observed at the 3ʹ-end in kallar grass (Leptochloa fusca). Transcript profiling of HvHKT2;1 in barley showed differential splicing events, which were regulated by NaCl concentration in soil. Accumulation of intron retaining transcripts was observed with abundance of short intron retaining HKT isoforms. Conventional PCR detected different splice variants which were cloned and sequenced. Intron retaining full length cDNA (HvHKT2;1-i) was transformed in tobacco (Nicotiana tabacum) and arabidopsis. Different HvHKT2;1 isoforms were detected in model plant systems with abundance of short intron retaining transcripts. Furthermore, HKT transcript analysis in both model plant systems showed similar results as observed in barley under native promoter conditions. To functionally characterize HvHKT2;1-i, a wild type and potassium uptake deficient mutant yeast strain (trk1, trk2) was used. Both, the wild type and trk1, trk2 yeast expressing HvHKT2;1-i, showed growth activities on YPD (Yeast Peptone Dextrose) solid medium. Growth sensitivities of both wild type and the trk1, trk2 yeast were observed on YPD solid medium containing hygromycin under similar conditions. Addition of milimolar (mM) concentrations of KCl and NaCl in hygromycin supplemented YPD solid resulted in growth recovery of trk1, trk2 yeast expressing HvHKT2;1-i suggesting the presence of functional transcripts in the pool of intron retaining transcripts. It is also clear from yeast functional analysis that HvHKT2;1-i cDNA with introns still enabled the trk1, trk2 yeast to complement K+/Na+ phenotype xiii while maintaining the high affinity K+ transport function. Expression analysis from barley, putative transgenic Arabidopsis, transgenic tobacco and the trk1, trk2 yeast mutant expressing HvHKT2;1-i, showed alternate splicing, intron retention and differential splicing events. Changes in HKT transcript patterns in response to varying K+ and Na+ concentrations, in both heterologous and plant system, suggest a role of these ions in regulation of HKT expression under salt stress. Nicotiana benthamiana plants were used for transient expression of HvHKT2;1-i. Confocal studies detected GFP signals on plasma membrane suggesting the presence of functional HvHKT2;1 fusion protein and hence, the evidence of properly spliced transcripts.