Photosynthesis Responses and Salt Tolerant Gene Identification in Chromosome Substitution Line of Khao Dawk Mali 105 Rice

The chromosome segment substitution lines (CSSLs) of rice with ‘Khao Dawk Mali105’ (KDML105) rice genetic background containing the putative salt tolerant region on chromosome1 (chr1) of DH212 rice located between RM1003 to RM3362 markers were examined in order to evaluate salt tolerant ability. CSSL11, CSSL12 and CSSL16 containing the full segment of the putative salt tolerant region based on marker assisted detection were compared with parental lines, KDML105 and DH212. CSSL16 revealed the significantly more tolerant to salt stress than KDML105 rice. Therefore, the whole genome sequence analysis was performed to compare CSSL16 and KDML105 genomes. The major regions that are different between two lines are on chromosome 1, 4 and 7. The different loci between CSSL16 and KDML105 were subjected to co-expression network analysis and ten major node genes were found. Six of them were genes functioned in chloroplast. The pattern of gene expression of PsbS1 of CSSL16 was similar to DH212, but different from KDML105. Rice PsbS1 is homologous to CP22 in Arabidopsis, which encodes chlorophyll a, b-binding proteins, localized in PSII and responsible for non-photochemical quenching process. Therefore, salt stress effects were determined in cp22 knocked-out mutant line. The mutation in cp22 led to the more susceptibility to salt stress. The dramatic reduction in quantum yield efficiency of PSII (F_v/F_m), and growth was found in cp22 mutant line, when compared to wild type grown under salt stress condition. These results suggested rice PsbS1 may play an important role for maintenance and adaptation ability in photosynthesis under SS.