Beyond iron-storage pool: functions of plant apoplastic iron during stress.

Iron (Fe) is an essential micronutrient for plants, and its storage in the apoplast represents an important Fe pool. Plants have developed various strategies to reutilize this apoplastic Fe pool to adapt to Fe deficiency. In addition, growing evidence indicates that the dynamic changes in apoplastic Fe are critical for plant adaptation to other stresses, including ammonium stress, phosphate deficiency, and pathogen attack. In this review, we discuss and scrutinize the relevance of apoplastic Fe for plant behavior changes in response to stress cues. We mainly focus on the relevant components that modulate the actions and downstream events of apoplastic Fe in stress signaling networks.

Dissecting yield-associated loci in super hybrid rice by resequencing recombinant inbred lines and improving parental genome sequences.

The growing world population and shrinkage of arable land demand yield improvement of rice, one of the most important staple crops. To elucidate the genetic basis of yield and uncover its associated loci in rice, we resequenced the core recombinant inbred lines of Liang-You-Pei-Jiu, the widely cultivated super hybrid rice, and constructed a high-resolution linkage map. We detected 43 yield-associated quantitative trait loci, of which 20 are unique. Based on the high-density physical map, the genome sequences of paternal variety 93-11 and maternal cultivar PA64s of Liang-You-Pei-Jiu were significantly improved. The large recombinant inbred line population combined with plentiful high-quality single nucleotide polymorphisms and insertions/deletions between parental genomes allowed us to fine-map two quantitative trait loci, qSN8 and qSPB1, and to identify days to heading8 and lax panicle1 as candidate genes, respectively. The quantitative trait locus qSN8 was further confirmed to be days to heading8 by a complementation test. Our study provided an ideal platform for molecular breeding by targeting and dissecting yield-associated loci in rice.

Characterization of physiological response and identification of associated genes under heat stress in rice seedlings.

Global warming, which is caused by greenhouse gas emissions, makes food crops more vulnerable to heat stress. Understanding the heat stress-related mechanisms in crops and classifying heat stress-related genes can increase our knowledge in heat-resistant molecular biology and propel developments in molecular design breeding, which can help rice cope with unfavorable temperatures. In this study, we carried out a physiological analysis of rice plants after heat stress. The results show a dramatic increase in malondialdehyde contents and SOD activities. We successfully isolated 11 heat-related rice genes with known function annotation through DNSH, which is an improved SSH method for screening long cDNA fragments. The reanalysis of microarray data from public database revealed that all these genes displayed various expression patterns after heat stress, drought, cold and salt. Quantitative real-time reverse transcription PCR was also performed to validate the expression of these genes after heat stress. The expressions in 10 genes were all significantly changed except for contig 77, which is a CBL-interacting protein kinase. Several reports have been published about the members of the same gene family.

Identification of QTLs for yield and yield components of barley under different growth conditions.

Waterlogging is a major abiotic stress limiting barley (Hordeum vulgare L.) yield and its stability in areas with excessive rainfall. Identification of genomic regions influencing the response of yield and its components to waterlogging stress will enhance our understanding of the genetics of waterlogging tolerance and the development of more tolerant barley cultivars. Quantitative trait loci (QTLs) for grain yield and its components were identified using 156 doubled haploid (DH) lines derived from a cross between the cultivars Yerong (waterlogging-tolerant) and Franklin (waterlogging-sensitive) grown under different conditions (waterlogged and well drained). A total of 31 QTLs were identified for the measured characters from two experiments with two growth environments. The phenotypic variation explained by individual QTLs ranged from 4.74% to 55.34%. Several major QTLs determining kernel weight (KW), grains per spike (GS), spikes per plant (SP), spike length (SL) and grain yield (GY) were detected on the same region of chromosome 2H, indicating close linkage or pleiotropy of the gene(s) controlling these traits. Some different QTLs were identified under waterlogging conditions, and thus different markers may have to be used in selecting cultivars suitable for high rainfall areas.

Genetic mapping of quantitative trait loci associated with beta-amylase and limit dextrinase activities and beta-glucan and protein fraction contents in barley.

High malting quality of barley (Hordeum vulgare L.) relies on many traits, such as beta-amylase and limit dextrinase activities and beta-glucan and protein fraction contents. In this study, interval mapping was utilized to detect quantitative trait loci (QTLs) affecting these malting quality parameters using a doubled haploid (DH) population from a cross of CM72 (six-rowed) by Gairdner (two-rowed) barley cultivars. A total of nine QTLs for eight traits were mapped to chromosomes 3H, 4H, 5H, and 7H. Five of the nine QTLs mapped to chromosome 3H, indicating a possible role of loci on chromosome 3H on malting quality. The phenotypic variation accounted by individual QTL ranged from 8.08% to 30.25%. The loci of QTLs for beta-glucan and limit dextrinase were identified on chromosomes 4H and 5H, respectively. QTL for hordeins was coincident with the region of silica eluate (SE) protein on 3HS, while QTLs for albumins, globulins, and total protein exhibited overlapping. One locus on chromosome 3H was found to be related to beta-amylase, and two loci on chromosomes 5H and 7H were found to be associated with glutelins. The identification of these novel QTLs controlling malting quality may be useful for marker-assisted selection in improving barley malting quality.

RETARDED PALEA1 controls palea development and floral zygomorphy in rice.

Poaceae, one of the largest flowering plant families in angiosperms, evolved distinct inflorescence and flower morphology diverging from eudicots and other monocots. However, the mechanism underlying the specification of flower morphology in grasses remains unclear. Here we show that floral zygomorphy along the lemma-palea axis in rice (Oryza sativa) is partially or indirectly determined by the CYCLOIDEA (CYC)-like homolog RETARDED PALEA1 (REP1), which regulates palea identity and development. The REP1 gene is only expressed in palea primordium during early flower development, but during later floral stages is radially dispersed in stamens and the vascular bundles of the lemma and palea. The development of palea is significantly retarded in the rep1 mutant and its palea has five vascular bundles, which is similar to the vascular pattern of the wild-type lemma. Furthermore, ectopic expression of REP1 caused the asymmetrical overdifferentiation of the palea cells, altering their floral asymmetry. This work therefore extends the function of the TCP gene family members in defining the diversification of floral morphology in grasses and suggests that a common conserved mechanism controlling floral zygomorphy by CYC-like genes exists in both eudicots and the grasses.

QTL analysis of flag leaf in barley (Hordeum vulgare L.) for morphological traits and chlorophyll content.

To understand genetic patterns of the morphological and physiological traits in flag leaf of barley, a double haploid (DH) population derived from the parents Yerong and Franklin was used to determine quantitative trait loci (QTL) controlling length, width, length/width, and chlorophyll content of flag leaves. A total of 9 QTLs showing significantly additive effect were detected in 8 intervals on 5 chromosomes. The variation of individual QTL ranged from 1.9% to 20.2%. For chlorophyll content expressed as SPAD value, 4 QTLs were identified on chromosomes 2H, 3H and 6H; for leaf length and width, 2 QTLs located on chromosomes 5H and 7H, and 2 QTLs located on chromosome 5H were detected; and for length/width, 1 QTL was detected on chromosome 7H. The identification of these QTLs associated with the properties of flag leaf is useful for barley improvement in breeding programs.