Relationship between OsCam1-1 and OsNUC1 gene expression in salt-stress respone in rice Oryza sativa L.

Abstract

Nucleolin1 (OsNUC1) is a salt stress-responsive gene of which the role in rice is implicated in salt tolerance. The principal objective of this study was to understand the regulation of OsNUC1 gene expression under salinity stress. Promoter region of OsNUC1 was cloned from two pairs of rice cultivars/lines; including a salt-sensitive cultivar, Leung Pra Tew 123 (LPT123), and its salt-resistant mutated line, Leung Pra Tew 123-TC171 (LPT123-TC171), as well as a salt-sensitive cultivar, Khao Dawk Mali 105 (KDML105) and its salt-resistant introgression line, FL530-IL. It was found that nucleotide sequence of OsNUC1 promoter contained important cis-regulatory elements that are associated with dehydration/salt responsive gene expression, i. e. MYB and MYC recognition sites, dehydration responsive element (DRE), and ABA-responsive elements (ABREs). Sequence comparison among the four rice cultivars/lines revealed that OsNUC1 promoter from the cultivar LPT123 and KDML105 were identical. However, They were different from those of LPT123-TC171 and FL530-IL in that the promoter of those lines exhibited greater number of MYB and MYC recognition sites and ABREs. These cis-element variations found on the gene promoter might be a cause for the distinct OsNUC1 expression patterns/levels in response to salinity amongst the rice cultivars/lines. Furthermore, the effect of the salt-stress sensor OsCam1-1 on OsNUC1 gene expression under salinity was assessed. It was found that salt stress-responsive expression of OsNUC1 was positively correlated with OsCam1-1 transcript levels, suggesting the involvement of Ca2+/calmodulin signaling in regulation of OsNUC1 gene expression under salinity. Moreover, in this study, putative calmodulin-binding R2R3-MYB transcription factors were identified from the rice genome, seven of which showed potential to interact with calmodulin. Four of the putative R2R3-MYB proteins were selected for a test of interaction with the salt-stress sensor OsCaM1-1 by yeast two-hybrid assay. However, the assay revealed the absence of protein interaction.