Sustained low abscisic acid levels increase seedling vigor under cold stress in rice (Oryza sativa L.).
Stress-induced abscisic acid (ABA) is mainly catabolized by ABA 8'-hydroxylase (ABA8ox), which also strictly regulates endogenous ABA levels. Although three members of the ABA8ox gene family are conserved in rice, it is not clear which stressors induce expression of these genes. Here, we found that OsABA8ox1 was induced by cold stress within 24 h and that OsABA8ox2 and OsABA8ox3 were not. In contrast, OsABA8ox2 and OsABA8ox3 were ABA-inducible, but OsABA8ox1 was not. OsABA8ox1, OsABA8ox2, and OsABA8ox3 restored germination of a cyp707a1/a2/a3 triple mutant of Arabidopsis to rates comparable to those of the wild type, indicating that OsABA8ox1, OsABA8ox2, and OsABA8ox3 function as ABA-catabolic genes in vivo. Transgenic rice lines overexpressing OsABA8ox1 showed decreased levels of ABA and increased seedling vigor at 15 °C. These results indicate that sustained low levels of ABA lead to increased seedling vigor during cold stress. On the other hand, excessively low endogenous ABA levels caused reduced drought and cold tolerance, although some of the transgenic rice lines expressing OsABA8ox1 at moderate levels did not show these harmful effects. Adequate regulation of endogenous ABA levels is thought to be crucial for maintaining seedling vigor under cold stress and for cold and drought tolerance in rice.
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Ryosuke
R
Mega
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Ayano
A
Meguro-Maoka
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Akira
A
Endo
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Etsuo
E
Shimosaka
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Seiji
S
Murayama
Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, Ontario M5S 3B2, Canada.
Eiji
E
Nambara
Dormancy and Adaptation Research Unit, RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
Mitsunori
M
Seo
Dormancy and Adaptation Research Unit, RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
Yuri
Y
Kanno
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C7, Canada.
Suzanne R
SR
Abrams
Crop Breeding Research Division, National Agriculture and Food Research Organization (NARO), Hokkaido Agricultural Research Center, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan.
Yutaka
Y
Sato
D000040:Abscisic Acid / Q000378:metabolism*; D016000:Cluster Analysis; D003080:Cold Temperature; D055864:Droughts; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D009154:Mutation; D012275:Oryza / Q000187:drug effects / Q000502:physiology*; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology; D036226:Seedlings; D013312:Stress, Physiological
D010937:Plant Growth Regulators; D000040:Abscisic Acid