Mutations of genes in synthesis of the carotenoid precursors of ABA lead to pre‐harvest sprouting and photo‐oxidation in rice

Jun Fang,Jiuyou Tang,Chengcai Chu,Yiqin Wang,Zejun Huang,Zhukuan Cheng,Congming Lu,Qian Qian,Lei Sun,Chunlai Li,Qingtao Lu,Min Liu,Changhui Sun,Xiaoli Guo,Fan Chen,Yan Zhang,Chenglin Chai,Bin Han

doi:10.1111/j.1365-313x.2008.03411.x

Abstract

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), ζ-carotene desaturase (OsZDS), carotenoid isomerase (OsCRTISO) and lycopene β-cyclase (β-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/phs3-1 mutant 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.

Highlights

Our results suggested that the impairment in synthesis of the carotenoid precursors of abscisic acid (ABA) leads to photo-oxidation and pre-harvest sprouting (PHS) in rice, which will definitely be helpful for elucidating the molecular mechanisms of PHS in other crops such as wheat and barley that are susceptible to PHS
16 000 transgenic T1 lines were screened prior to harvest by visual inspection in the paddy field, and 27 putative mutants were identified with a viviparous phenotype
To get further evidence for the photo-oxidative damage occurring in photosystem II (PS II), we examined the levels of essential PS II core proteins CP43, CP47 and D1 (Green and Durnford, 1996), which are the targets of reactive oxygen species (ROS) (Niyogi, 1999), in the leaves from the phs3-1 mutant and b-OsLCY-RNAi plants, respectively

Summary

Introduction

A 2008 The Authors Journal compilation a 2008 Blackwell Publishing Ltd harvest, is termed pre-harvest sprouting (PHS) or vivipary. Pre-harvest sprouting of cereal grains causes reduction of grain yield and affects the quality of the grain. Previous work demonstrated that mutants impaired in abscisic acid (ABA) biosynthesis or responsiveness, such as maize viviparous (vp), Arabidopsis ABA-deficient (aba) and ABA-insensitive (abi) mutants, often produce precociously germinating seeds (McCarty, 1995). At least 10 viviparous mutants have been identified from maize (Zea mays L.), most of which (vp, vp5, vp, vp9, w3, y3, and y9) were blocked in biosynthesis of the carotenoid precursors for de novo ABA synthesis (Figure S1; Singh et al, 2003). A series of steps including cyclization and hydroxylation reactions take place to yield a-carotene, b-carotene, lutein, xanthophyll, and zeaxanthin. The C40 carotenoid precursor is cleaved and followed by a two-step conversion of the intermediate xanthoxin to ABA via ABA aldehyde (Schwartz et al, 2003; Xiong and Zhu, 2003)

Results

Discussion

Conclusion