Genes that are uniquely stress regulated in salt overly sensitive (sos) mutants

Abstract

Repetitive rounds of differential subtraction screening, followed by nucleotide sequence determination and northern-blot analysis, identified 84 salt-regulated (160 mM NaCl for 4 h) genes in Arabidopsis wild-type (Col-0 gl1) seedlings. Probes corresponding to these 84 genes and ACP1, RD22BP1, MYB2, STZ, and PAL were included in an analysis of salt responsive gene expression profiles in gl1 and the salt-hypersensitive mutant sos3. Six of 89 genes were expressed differentially in wild-type and sos3 seedlings; steady-state mRNA abundance of five genes (AD06C08/unknown, AD05E05/vegetative storage protein 2 [VSP2], AD05B11/S-adenosyl-L-Met:salicylic acid carboxyl methyltransferase [SAMT], AD03D05/cold regulated 6.6/inducible2 [COR6.6/KIN2], and salt tolerance zinc finger [STZ]) was induced and the abundance of one gene (AD05C10/circadian rhythm-RNA binding1 [CCR1]) was reduced in wild-type plants after salt treatment. The expression of CCR1, SAMT, COR6.6/KIN2, and STZ was higher in sos3 than in wild type, and VSP2 and AD06C08/unknown was lower in the mutant. Salt-induced expression of VSP2 in sos1 was similar to wild type, and AD06C08/unknown, CCR1, SAMT, COR6.6/KIN2, and STZ were similar to sos3. VSP2 is regulated presumably by SOS2/3 independent of SOS1, whereas the expression of the others is SOS1 dependent. AD06C08/unknown and VSP2 are postulated to be effectors of salt tolerance whereas CCR1, SAMT, COR6.6/KIN2, and STZ are determinants that must be negatively regulated during salt adaptation. The pivotal function of the SOS signal pathway to mediate ion homeostasis and salt tolerance implicates AD06C08/unknown, VSP2, SAMT, 6.6/KIN2, STZ, and CCR1 as determinates that are involved in salt adaptation.

Figure 1

Salt-responsive gene expression that is dependent on the SOS pathway in Arabidopsis. Genes that are differentially regulated in wild-type (Col-0 gl1) and sos3. Total RNA (40 μg) from seedlings grown in liquid culture (14 d) and treated without or with 160 mm NaCl for 4 h. The northern blot was hybridized with ³²P-labeled probe corresponding to: COR6.6/KIN2, SAMT, CCR1, VSP2, and AD06C08 (unknown). AtGAPDH (glyceraldehyde-3-phosphate-dehydrogenase) is the control.

Figure 2

Comparative expression of genes dependent on the SOS pathway in wild type (Col-0 and gll) and sos1, sos2, and sos3. Illustrated is the northern blot of steady-state mRNA levels of COR6.6/KIN2, SAMT, CCR1, and VSP2 in plants without (0 h) or 160 mm NaCl (24 h). Ethidium bromide staining was used to monitor RNA loading.

Figure 3

Illustrated is a model depicting the SOS pathway regulation of salt responsive genes. Hypersaline conditions activate the SOS (SOS3 → SOS2 → SOS1) signal pathway (Zhu, 2000) and transcript abundance of AD0608 (unknown), VSP2 (vegetative storage protein 2, AD05E05), SAMT (S-adenosyl-l-Met:salicylic acid carboxyl methyltransferase, AD05B11), COR6.6/KIN2 (cold regulated 6.6/inducible 2, AD03D05 [COR6.6/KIN2], and STZ [salt tolerance zinc finger], Lippuner et al., 1996) increase and of CCR1 (circadian rhythm-RNA binding1, AD05C10) decreases in Arabidopsis seedlings. Positive (↓) or negative (⊥) regulation by the SOS pathway is indicated.