Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı 2

Expressıon Analysıs Of Starch Branching Enzymes In Lentıl (Lens Culınarıs Medık.) Under Dıfferent Photoperıods
Lentil is a long-day plant of Legume (Fabaceae) family and contains a considerable amount of starch and proteins. Due to these characteristics, lentil is an important food source especially in developing countries. Recent studies have shown that plant yields could be improved with the manipulation of starch enzymes. For this purpose, characterisation of the enzymes which are responsible for the starch biosynthesis [ADP-glucose pyrophosphorylase (AGPase; EC 2.7.7.23), starch branching enzyme (SBE; EC 2.4.1.28) and soluble starch synthase (SSS; EC 2.4.1.21)] is very important. The effect of the photoperiyod length on the tissue expression of the genes encoding AGPase subunits and SSSI-III enzymes has been determined previously. However, expression profile of starch branching enzyme has not been studied. It is known that starch branching enzyme is categorized as A (SBEII) and B (SBEI) on the basis of amino acid sequences and in-vitro catalytic characteristics of purified proteins. Genes that are coding SBEI are generally expressed in photosynthetic and vegetative tissues, genes that are coding SBEII are expressed in parts where the starch is stored.
In this thesis, we investigated the transcription profiles of SBEI-II genes in lentil growing under long-day (16-h light/8-h dark) and short-day (8- h light/16-h dark) photoperiod conditions. Briefly, (1) SBEI and SBEII genes show higher expression in leaf tissue. (2) When compared with SBEI, SBEII gene transcripts are more abundant in both tissues. (3) Shortened photoperiod length has effect on the transcription of both genes. Overall transcription of lentil SBEI decreased by approximately 30% in stems under a short-day photoperiyod regime. Overall transcription of lentil SBEII decreased by approximately 50% in leaves, increased by approximately 50% in stems under a short-day regime. (4) Both SBE genes showed rhytmic fluctuations with gene expression peaks in every 4-6hrs. SBE gene expression pattern observed in long-day 16 hr light time interval was adapted to short-day 8 hr light time interval. (5) When the expression of SBEII and SSSI (Soluble starch synthase) genes is compared, similar gene expression pattern was observed in both tissues. The findings of similar expression profiles of SBEII and SSSI and abundant expression of SBEII are in consistance with the trimeric structure model of SBEII-SSSI enzymes.
In the scope of this study, the effect of the photoperiod length on tissue expression profiles of SBEI and SBEII genes has been determined. Similar tissue expression profiles of SBEII and SSSI genes are in consistance with the studies proposing the SBEII and SSSI enzymes trimeric structure in cytosol. This study complements the previous studies carried out by our research group targeting the characterization of genes encoding the enzymes involved in starch biosynthesis. Together with the previous studies, the effect of the photoperiod on tissue expression profiles of AGPaseL1-2, AGPaseS1-2, SBEI-II, SSSI-III genes has been determined. Kinetic analyses of SBEI-II enzymes are needed to complete this study. Expression and kinetic analyses results will help us to undestand the regulation of enzymes involved in starch biosynthesis in Lentile, an important member of Fabaceae family. Understanding the starch biosynhesis mechanism will contribute the studies aiming to increase the plant growth and yield.