Mutations of genes in synthesis of the carotenoid precursors of ABA lead to pre-harvest sprouting and photo-oxidation in rice.
Pre-harvest sprouting (PHS) or vivipary in cereals is an important agronomic trait that results in significant economic loss. A considerable number of mutations that cause PHS have been identified in several species. However, relatively few viviparous mutants in rice (Oryza sativa L.) have been reported. To explore the mechanism of PHS in rice, we carried out an extensive genetic screening and identified 12 PHS mutants (phs). Based on their phenotypes, these phs mutants were classified into three groups. Here we characterize in detail one of these groups, which contains mutations in genes encoding major enzymes of the carotenoid biosynthesis pathway, including phytoene desaturase (OsPDS), zeta-carotene desaturase (OsZDS), carotenoid isomerase (OsCRTISO) and lycopene beta-cyclase (beta-OsLCY), which are essential for the biosynthesis of carotenoid precursors of ABA. As expected, the amount of ABA was reduced in all four phs mutants compared with that in the wild type. Chlorophyll fluorescence analysis revealed the occurrence of photoinhibition in the photosystem and decreased capacity for eliminating excess energy by thermal dissipation. The greatly increased activities of reactive oxygen species (ROS) scavenging enzymes, and reduced photosystem (PS) II core proteins CP43, CP47 and D1 in leaves of the Oscrtiso/phs3-1mutant and OsLCY RNAi transgenic rice indicated that photo-oxidative damage occurred in PS II, consistent with the accumulation of ROS in these plants. These results suggest that the impairment of carotenoid biosynthesis causes photo-oxidation and ABA-deficiency phenotypes, of which the latter is a major factor controlling the PHS trait in rice.
Fang
Jun
J
State Key Laboratory of Plant Genomics and National Centre for Plant Gene Research, Beijing 100101, China.
Chai
Chenglin
C
Qian
Qian
Q
Li
Chunlai
C
Tang
Jiuyou
J
Sun
Lei
L
Huang
Zejun
Z
Guo
Xiaoli
X
Sun
Changhui
C
Liu
Min
M
Zhang
Yan
Y
Lu
Qingtao
Q
Wang
Yiqin
Y
Lu
Congming
C
Han
Bin
B
Chen
Fan
F
Cheng
Zhukuan
Z
Chu
Chengcai
C
D000040:Abscisic Acid / Q000096:biosynthesis*; D002338:Carotenoids / Q000096:biosynthesis / Q000378:metabolism*; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D018525:Germination / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D010084:Oxidation-Reduction; D012639:Seeds / Q000235:genetics / Q000502:physiology
D002338:Carotenoids; D000040:Abscisic Acid