Drought stress limits plant growth and productivity. It triggers many responses by inducing changes in plant morphology and physiology. KDML105 rice is a key rice variety in Thailand and is normally grown in the northeastern part of the country. The chromosome segment substitution lines (CSSLs) were developed by transferring putative drought tolerance loci (QTLs) on chromosome 1, 3, 4, 8, or 9 into the KDML105 rice genome. CSSL104 is a drought-tolerant line with higher net photosynthesis and leaf water potential than KDML105 rice. The analysis of CSSL104 gene regulation identified the loci associated with these traits via gene co-expression network analysis. Most of the predicted genes are involved in the photosynthesis process. These genes are also conserved in Arabidopsis thaliana. Seven genes encoding chloroplast proteins were selected for further analysis through characterization of Arabidopsis tagged mutants. The response of these mutants to drought stress was analyzed daily for seven days after treatment by scoring green tissue areas via the PlantScreen™ XYZ system. Mutation of these genes affected green areas of the plant and stability index under drought stress, suggesting their involvement in drought tolerance.
This research aims to evaluate the photosynthesis-related parameters in rice chromosome segment substitution lines (CSSL), containing drought-tolerant region from DH212 in a Khao Dawk Mali105 genetic background. Screening at seedling stage indicated that CSSL4 was more tolerant to drought stress than KDML105 with the higher maximal quantum yield of PSII photochemistry. After withholding water, the decline in light-saturated net photosynthetic rate due to drought stress occurred simultaneously with the decrease in electron transport rate and effective quantum yield of PSII photochemistry values, suggesting that stomatal changes affect light-saturated net photosynthetic rate (PNmax) during the initial drought response. KDML105 rice showed the highest level of electron transport rate/PNmax ratio. This suggested that KDML105 h a s the lowest ability to use reducing power in photosynthesis process under drought stress conditions. Loci containing single nucleotide polymorphisms between CSSL4 and KDML105 were subjected for co-expression network analysis with 0.99 correlation. The co-expression between calmodulin-stimulated calcium-ATPase and C2H2 zinc finger protein was detected. This locus may contribute to the maintenance ability of photosynthesis process under drought stress conditions.
Salt stress affects plant growth and productivity. In this study we determined the roles of eight genes involved in photosynthesis, using gene co-expression network analysis, under salt-stress conditions using Arabidopsis knockout mutants. The green area of the leaves was minimum in the at1g65230 mutant line. Rice LOC_Os01g68450, a homolog of at1g65230, was ectopically expressed in the at1g65230 mutant line to generate revertant lines. Under salt stress, the revertant lines exhibited significantly higher net photosynthesis rates than the at1g65230 mutant line. Moreover, the operating efficiency of photosystem II (PSII) and electron transport rate of the revertant lines were higher than those of the wild type and at1g65230 mutant line after 10 days of exposure to salt stress. After this period, the protein PsbD–the component of PSII–decreased in all lines tested without significant difference among them. However, the chlorophyll a and b, carotenoid, and anthocyanin contents of revertant lines were higher than those of the mutant line. Furthermore, lower maximum chlorophyll fluorescence was detected in the revertant lines. This suggests that LOC_Os01g68450 expression contributed to the salt tolerance phenotype by modifying the energy dissipation process and led to the ability to maintain photosynthesis under salt stress conditions.
Abiotic stresses, especially drought and salt stresses can affect plant growth and productivity. ‘Kao Dawk Mali 105’ (‘KDML105’) rice is one of the crops which has to face both drought and salt stresses as it is grown in rain-fed saline soil in the northeastern region of Thailand, where the irrigation is limited. CSSL104, a chromosome substitution line with ‘KDML105’ genetic background, was developed in order to improve drought tolerant ability of ‘KDML105’ rice by transferring the drought tolerant (DT)-QTL region from double haploid line, DH103. Photosynthesis parameters of CSSL104 and its parental lines, ‘KDML105’ and DH103, were investigated, when they were grown in normal and drought-stress conditions. Net photosynthesis rates of all lines were similar in normal condition. In drought stress, net photosynthesis rate of all lines was declined, but CSSL104 and DH103 rice had the significant higher photosynthetic rate than ‘KDML105’ rice under drought-stressed condition. Based on the SNPs comparison between CSSL104 and ‘KDML105’ rice and gene co-expression network analysis, nine genes were involved in photosynthesis and six genes from those genes were used to study in Arabidopsis mutant lines containing the mutation in the homologous genes of the predicted ones. The mutant lines containing the mutation in LOC_Os01g72950, LOC_Os07g37550, LOC_Os07g38300, and LOC_Os10g10170 showed better growth than wild type (WT) under drought stress. The expression of LOC_Os07g37550 and LOC_Os08g41460 in ‘KDML105’ was higher than the expression in CSSL104 and DH103 under drought stress. It supported the result of net photosynthesis that ‘KDML105’ was more susceptible to drought stress than CSSL104 and DH103. Therefore, it was proposed that these genes were involved in drought tolerant mechanism in CSSL104. The predicted drought tolerance genes from CSSL104, Ndh-O, Lhcb3, Rrf, Pgrl5-like, LOC_Os09g39390, Mrl1, together with LOC_Os01g68450, the predicted salt tolerance gene from CSSL16 were evaluated for salt tolerance involvement by using the Arabidopsis mutant lines containing the mutation in the homologous genes of the predicted ones. At1g65230 is orthologous to LOC_Os01g68450 gene in rice and at1g65230 Arabidopsis mutant performed the highest growth inhibition under salt stress condition when compared to other mutant lines. The revertant and ectopic expression lines with LOC_Os01g68450 gene show the higher growth parameters than the at1g65230 mutant under drought and salt stress. Moreover, the ectopic expression lines showed high net photosynthesis and pigments content under salt stress. These suggested that LOC_Os01g68450 gene has a function to maintain pigments contents under drought and salt stress leading to the photosynthesis adaptation during drought and salt stress.
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