DECIPHERING THE DIFFERENTIALLY EXPRESSED HEAT STRESS RESPONSIVE CANDIDATE GENES IN RICE (Oryza sativa)
Loading...
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Global warming is expected to increase the earth’s surface mean temperatures by 1.5 to 4.8 ºC by 2100 (IPCC 2014) and it is reported to reduce the yield of major crop plants including rice by 41% by the end of 21st century. Rice is the most important staple food crop across the world and feeds more than 3 billion people in Asia and Africa. Heat stress affects the growth of rice crop at all stages of growth like vegetative, reproductive and ripening phases but the effect is severe during flowering stage, as it leads to spikelet sterility that causes reduced yields. Improved varieties of rice with heat tolerance are required to meet the complex challenges like increasing population, decreasing arable land and increasing temperatures. Expression analysis of genes responsive to heat stress in different crops will be of great importance in today’s agriculture.
Transcriptome sequencing of rice after exposure to high temperature treatments could provide information on genes, that are differentially regulated on exposure to heat stress and its dissection is necessary to identify and characterize key genes responsible for heat tolerance. High temperatures produces the new group of special proteins under stress called as ‘Heat Shock Proteins (HSPs)’, which are categorized into five families based on their molecular weights: 1) small heat-shock proteins (sHSPs), 2) Hsp60, 3) Hsp70, 4) Hsp90 and 5) Hsp100. Studies reported plants synthesize large amounts of sHSPs under heat stress functioning as molecular chaperons, suggesting that they play a major role for enduring thermo-tolerance in plants. Higher plants posses at least 20 sHSPs. Transcription of HSPs is guarded by some regulatory proteins, called heat stress transcription factors (Hsfs). At least 21 Hsfs are seen in plants, with its specific role in regulation. Heat shock proteins perform a major role in signalling, translation, host-defence mechanisms, carbohydrate metabolism and amino acid metabolism by maintaining the functional conformation of proteins, preventing accumulation of non-native proteins and refolding. sHSPs facilitate stabilization of denatured proteins under heat stress. Based on this, the current study was planned to identify some key genes that are responsible for heat tolerance in fourteen rice genotypes (GP-145-103, SL-62, Dagaddeshi, Nagina-22, Swarna, GP-145-55, CGZR-1, Annada, Poornima, Karma mashuri, ARB-6-11, GP-145-40, MTU-1010, RRF-127) at late vegetative stage before panicle initiation. Genotypes belonging to diverse genetic background were grown in two sets under control and stress conditions (42˚C) for identifying heat tolerant traits. Phenological and biochemical characterization of rice genotypes was done under heat stress and in parallel a set of known heat related candidate genes were selected for expression analysis studies using semi-quantitative RT-PCR analysis. Under phenological and biochemical characterization six parameters are taken into consideration. They are membrane stability index (MSI), pollen fertility, spikelet fertility, chlorophyll content, proline and MDA levels.
Phenological and biochemical studies on rice resulted in identifying some of the tolerant and susceptible genotypes for heat stress. Genotypes RRF-127 , Nagina-22, Karma mashuri, CGZR-1 and Annada had recorded lower electrolyte leakage of 19.8%, 21.1%, 27.5%, 51.7% and 69.8% respectively under stress when compared to control. Lowest percentage of decrease in pollen fertility under stress conditions was observed in the genotypes RRF-127, Nagina-22, GP-145-103, Annada and CGZR-1 as 14.4%, 18.1%, 24.9%, 28.3% and 37.9% respectively. Percentage of Spikelet fertility decrease under stress was lowest in the genotypes RRF-127, Nagina-22, Annada, Karma mashuri and CGZR-1 as 14%, 19%, 25%, 31% and 42% respectively. When comparing the fold increase in proline content for stress over control, Nagina-22 showed highest fold increase of 20.6 folds followed by CGZR-1 (11.4 fold), RRF-127 (11.2 fold), Annada (10.5 fold), GP-145-103 (7.0 fold ) and Karma mashuri (6.0 fold). In chlorophyll content, Annada has the lowest fold decrease of 1.0 folds for all chla, chlb and total chlorophyll content followed by Karma mashuri (1.0 fold) under stress when compared with control. When comparing the fold increase in MDA content for stress over control. The lowest fold increase in MDA content was shown by RRF-127 with 1.1 fold increase followed by Nagina-22 (1.4 fold), CGZR-1 (1.5 fold), Annada (1.8 fold), GP-145-103 (2.1 fold) and Karma mashuri (2.5 fold).
Among the five genes (OsHSP26.7, OsHSP16.9, OsHSP DnaJ, OsHSP18 and 60Kda chaperon), selected for the study, OsHSP DnaJ has shown consistent expression under both control and stress with no significant change. The remaining four genes has shown up-regulation in all the genotypes under stress. OsHSP 26.7 gene has shown strong up-regulation in rice genotype RRF-127 (14.3 fold) followed by Annada (13.9 fold), Karma mashuri (11.5 fold), GP-145-103 (8.6 fold) and CGZR-1 (3.7 fold). OsHSP 16.9 gene has shown up-regulation in RRF-127 (10.0 fold) followed by Annada (3.7 fold), CGZR-1 (3.4 fold), GP-145-103 (3.2 fold) and Karma mashuri (3.1 fold). OsHSP 18 gene showed up-regulation in GP-145-103 (17.7 fold) followed by CGZR-1 (14.1 fold), Annada (13.8 fold), GP-145-55 (11.9 fold) and poornima (8.9 fold). 60Kda chaperon gene has shown up-regulation in almost all the genotypes under heat stress, but the up-regulation was by minimal levels. Among all the fourteen genotypes selected for the study, RRF-127, Annada, Karma mashuri, CGZR-1 and GP-145-103 showed a positive regulation towards heat stress and genotypes like MTU-1010, ARB-6-11 and GP-145-55 showed negative regulation towards heat stress. These findings were observed to be in correlation with the phenological and biochemical characterization and expression analysis studies carried out with five different heat responsive genes belonging to small heat shock proteins family, which had differential expression under heat stress when compared to control conditions. However positive induction of these genes leads to a key role in identification of different transcription factors, that have been responsible for different heat tolerant mechanisms or in cross-linking of different signalling pathways to activate plant defence mechanisms in rice under stress. This can be taken as a base for heat tolerance response of rice crop, which may be useful for further validation studies of the candidate genes responsive for heat stress in rice as well as other crop plants.
Description
DECIPHERING THE DIFFERENTIALLY EXPRESSED HEAT STRESS RESPONSIVE CANDIDATE GENES IN RICE (Oryza sativa)
Keywords
null