Linglong Liu

Pollen Semi-Sterility1 Encodes a Kinesin-1–Like Protein Important for Male Meiosis, Anther Dehiscence, and Fertility in Rice

This work describes Pollen Semi-Sterility1, a kinesin-1 like protein that is involved in regulating male meiosis in rice; in pss1 mutants, chromosome segregation is perturbed, causing reduced pollen viability and partial sterility. In flowering plants, male meiosis produces four microspores, which develop into pollen grains and are released by anther dehiscence to pollinate female gametophytes. The molecular and cellular mechanisms regulating male meiosis in rice (Oryza sativa) remain poorly understood. Here, we describe a rice pollen semi-sterility1 (pss1) mutant, which displays reduced spikelet fertility (~40%) primarily caused by reduced pollen viability (~50% viable), and defective anther dehiscence. Map-based molecular cloning revealed that PSS1 encodes a kinesin-1–like protein. PSS1 is broadly expressed in various organs, with highest expression in panicles. Furthermore, PSS1 expression is significantly upregulated during anther development and peaks during male meiosis. The PSS1–green fluorescent protein fusion is predominantly localized in the cytoplasm of rice protoplasts. Substitution of a conserved Arg (Arg-289) to His in the PSS1 motor domain nearly abolishes its microtubule-stimulated ATPase activity. Consistent with this, lagging chromosomes and chromosomal bridges were found at anaphase I and anaphase II of male meiosis in the pss1 mutant. Together, our results suggest that PSS1 defines a novel member of the kinesin-1 family essential for male meiotic chromosomal dynamics, male gametogenesis, and anther dehiscence in rice.

Inheritance and fine mapping of fertility restoration for cytoplasmic male sterility in Gossypium hirsutum L.

Abstract.Genetics of CMS fertility restoration was presented through the analysis of classic genetics and molecular markers. Based on F2 segregation of the crosses between CMS and the restoring lines, the testcrosses and F1 × F1 populations, together with RAPD and SSR mapping, one dominant gene was identified to control the CMS fertility restoration in cotton. The strategy of genotype representation analysis (GRA) was put forward to screen the markers linked with the Rf1 locus. Using 1,025 random decamer primers and 282 pairs of SSR primers, two RAPD and three SSR markers were identified to be closely linked to the Rf1 gene. Among the five markers, three were co-dominantly inherited. Additionally, based on the analysis of monosomic and telesomic lines with one SSR maker, the Rf1 locus could be located on the long arm of chromosome 4. The molecular markers available here are helpful in the development of the elite restoring lines in cotton by marker-assisted selection.

A knockdown mutation of YELLOW - GREEN LEAF2 blocks chlorophyll biosynthesis in rice

AbstractKey messageAn insert mutation ofYELLOW-GREEN LEAF2, encodingHeme Oxygenase 1, results in significant reduction of its transcript levels, and therefore impairs chlorophyll biosynthesis in rice.Abstract Heme oxygenase (HO) in higher plants catalyzes the degradation of heme to synthesize phytochrome precursor and its roles conferring the photoperiodic control of flowering in rice have been revealed. However, its involvement in regulating rice chlorophyll (Chl) synthesis is not fully explored. In this study, we isolated a rice mutant named yellow-green leaf 2 (ygl2) from a 60Co-irradiated population. Normal grown ygl2 seedlings showed yellow-green leaves with reduced contents of Chl and tetrapyrrole intermediates whereas an increase of Chl a/b ratio. Ultrastructural analyses demonstrated grana were poorly stacked in ygl2 mutant, resulting in underdevelopment of chloroplasts. The ygl2 locus was mapped to chromosome 6 and isolated via map-based cloning. Sequence analysis indicated that it encodes the rice HO1 and its identity was verified by transgenic complementation test and RNA interference. A 7-Kb insertion was found in the first exon of YGL2/HO1, resulting in significant reduction of YGL2 expressions in the ygl2 mutant. YGL2 was constitutively expressed in a variety of rice tissues with the highest levels in leaves and regulated by temperature. In addition, we found expression levels of some genes associated with Chl biosynthesis and photosynthesis were concurrently altered in ygl2 mutant. These results provide direct evidence that YGL2 has a vital function in rice Chl biosynthesis.

Identification and characterization of a novel Waxy allele from a Yunnan rice landrace

Low amylose content (AC) is a desirable trait for rice (Oryza sativa L.) cooking quality and is selected in soft rice breeding. To gain a better understanding of the molecular mechanism controlling AC formation, we screened 83 Yunnan rice landraces in China and identified a rice variety, Haopi, with low AC. Genetic analyses and transgenic experiments revealed that low AC in Haopi was controlled by a novel allele of the Wx locus, Wxhp, encoding a granule-bound starch synthase (GBSSI). Sequence comparisons of Wxhp and Wxb alleles (from Nipponbare) showed several nucleotide changes in the upstream regulatory regions (including the promoter, 5′-untranslated region, and first intron 5′ splicing junction site). Interestingly, these changes had no obvious effect on the expression level and splicing efficiency of Wx transcripts. In addition, an examination of the coding region revealed that the Wxhp allele carries an A-to-G change at nucleotide position +497 from the start codon, resulting in an Asp165/Gly165 substitution. The amino acid substitution had no detectable effects on GBSSI activity in vitro; however, it notably reduced the binding of GBSSI to starch granules, resulting in a reduction of AC in rice seeds. Moreover, three other Yunnan landraces with low AC also carry a nucleotide substitution identical to Haopi at the +497 position of the Wx gene, suggesting common ancestry. Based on the single-nucleotide polymorphism, we have developed a new derived cleaved amplified polymorphic sequence marker for use in breeding practice to manipulate AC in rice endosperm.

Albino midrib 1, encoding a putative potassium efflux antiporter, affects chloroplast development and drought tolerance in rice.

Key messageMutation of theAM1gene causes an albino midrib phenotype and enhances tolerance to drought in riceAbstractK+ efflux antiporter (KEA) genes encode putative potassium efflux antiporters that are mainly located in plastid-containing organisms, ranging from lower green algae to higher flowering plants. However, little genetic evidence has been provided on the functions of KEA in chloroplast development. In this study, we isolated a rice mutant, albino midrib 1 (am1), with green- and white-variegation in the first few leaves, and albino midrib phenotype in older tissues. We found that AM1 encoded a putative KEA in chloroplast. AM1 was highly expressed in leaves, while lowly in roots. Chloroplast gene expression and proteins accumulation were affected during chlorophyll biosynthesis and photosynthesis in am1 mutants. Interestingly, AM1 was induced by salt and PEG, and am1 showed enhanced sensitivity to salinity in seed germination and increased tolerance to drought. Taken together, we concluded that KEAs were involved in chloroplast development and played important roles in drought tolerance.

Accumulation of γ-Aminobutyric Acid in Giant-Embryo Rice Grain in Relation to Glutamate Decarboxylase Activity and Its Gene Expression During Water Soaking

ABSTRACT Glutamate decarboxylase (GAD) is the rate-limiting enzyme for γ-aminobutyric acid (GABA) synthesis. However, the relationship of GABA accumulation, GAD activity, and its gene expression in rice grain during water soaking is unknown yet. We assessed the role of GAD activity and its gene expression to GABA accumulation after the rice grain was soaked in water for 0, 1, 2, 4, 8, 16, and 32 hr. The results showed a continuous accumulation of GABA in steeped embryo, embryo-less brown rice, and complete brown rice, respectively. Among them, embryo of brown rice had the maximal accumulation. The activity of GAD was gradually increasing during water soaking, and the enzyme activity was significantly higher in the embryo than in either the embryo-less brown rice or whole brown rice. The results further indicated that the activity of GAD was markedly stimulated by 0.5 mmol/L of Ca2+, whereas it was almost completely inhibited by 1 mmol/L of Hg2+. Accordingly, the content of GABA in embryo paralleled the ac...

QTL Analysis of Aluminum Resistance in Rice (Oryza sativa L.)

Aluminum (Al) toxicity is considered as one of the primary causes of low-rice productivity in acid soils. In the present study, quantitative trait loci (QTLs) controlling Al resistance based on relative root elongation (RRE) were dissected using a complete linkage map and a recombinant inbred lines (RILs) derived from a cross of Al-tolerant japonica cultivar Asominori (Oryza sativa L.) and Al-sensitive indica cultivar IR24 (O. sativa L.). A total of three QTLs (qRRE-1, qRRE-9, and qRRE-11) were detected on chromosomes 1, 9, and 11 with LOD score ranging from 2.64 to 3.60 and the phenotypic variance explained from 13.5 to 17.7%. The Asominori alleles were all associated with Al resistance at all the three QTLs. The existence of these QTLs was confirmed using Asominori chromosome segment substitution lines (CSSLs) in IR24 genetic background (IAS). By QTL comparative analysis, the two QTLs (qRRE-1and qRRE-9) on chromosomes 1 and 9 appeared to be consistent among different rice populations while qRRE-11 was newly detected and syntenic with a major Al resistance gene on chromosome 10 of maize. This region may provide an important case for isolating genes responsible for different mechanisms of Al resistance among different cereals. These results also provide the possibilities of enhancing Al resistance in rice breeding program by marker-assisted selection (MAS) and pyramiding QTLs.

Marker assisted pyramiding of two brown planthopper resistance genes, Bph3 and Bph27 (t), into elite rice Cultivars

BackgroundBrown planthopper (BPH) is the most destructive insect in rice production. Breeding of resistant cultivars is the most cost-effective and environment-friendly strategy for BPH management; however, resistant cultivars are currently hampered by the rapid breakdown of BPH resistance. Thus, there is an urgent need to use more effective BPH resistance genes or pyramiding different resistance genes to develop more durable resistant rice cultivars.ResultsHere a dominant BPH resistance gene Bph27(t) were introgressed into a susceptible commercial japonica variety Ningjing3 (NJ3) and indica variety 93-11 using marker-assisted selection (MAS), respectively. Further, Bph27(t) and a durable BPH resistance gene Bph3 was pyramided by intercrossing single-gene introgressed lines through MAS. The introgression of BPH resistance genes significantly improved the BPH resistance and reduced the yield loss caused by BPH.ConclusionThe development of single and two genes pyramided lines in this study provides innovative resources for molecular breeding of durable BPH-resistant rice cultivars and BPH management through resistant cultivars.

Identification of Quantitative Trait Loci Associated with Aluminum Tolerance in Rice (Oryza Sativa L.)

SummaryQuantitative trait loci (QTL) analysis for Al tolerance was performed in rice using a mapping population of 98 BC1F10 lines (backcross inbred lines: BILs), derived from a cross of Al-tolerant cultivar of rice (Oryza sativa L. cv. Nipponbare) and Al-sensitive cultivar (cv. Kasalath). Three characters related to Al tolerance, including root elongation under non-stress conditions (CRE), root elongation under Al stress (SRE) and the relative root elongation (RRE) under Al stress versus non-stress conditions, were evaluated for the BILs and the parents at seedling stage. A total of seven QTLs for the three traits were identified. Among them, three putative QTLs for CRE (qCRE-6, qCRE-8 and qCRE-9) were mapped on chromosomes 6, 8 and 9, respectively. One QTL for SRE (qSRE-4) was identified on chromosome 4. Three QTLs (qRRE-5, qRRE-9 and qRRE-10) for RRE were detected on chromosomes 5, 9, 10 and accounted for 9.7–11.8% of total phenotypic variation. Interestingly, the QTL qRRE-5 appears to be syntenic with the genomic region carrying a major Al tolerance gene on chromosome 6 of maize. Another QTL, qRRE-9, appears to be similar among different rice populations, while qRRE-10 is unique in the BIL population. The common QTLs for CRE and RRE indicate that candidate genes conferring Al tolerance in the rice chromosome 9 may be associated with root growth rates. The existence of QTLs for Al tolerance was confirmed in substitution lines for corresponding chromosomal segments. These results also provide the possibilities of enhancing Al tolerance in rice through using marker-assisted selection (MAS) and pyramiding QTLs.

Dynamic QTL Analysis on Rice Fat Content and Fat Index Using Recombinant Inbred Lines

ABSTRACT Fat content (FC) and fat index (FI) play an important role in determining quality of eating and nutrition for rice. The objective of this study was to determine genetic information during the grain-filling period. Seventy-one recombinant inbred lines (RILs) derived from a cross between japonica cultivar Asominori and indica cultivar IR24 were used to analyze the developmental behavior of FC and FI by conditional and unconditional quantitative trait loci (QTL) mapping methods. At four developmental stages of grain filling, 11 unconditional QTL and 10 conditional QTL for FC as well as 11 unconditional QTL and eight conditional QTL for FI were identified. In unconditional QTL analysis, qFC-11-2 and qFI-3 were consistently detected at 21 and 28 days after flowering (DAF), whereas all the conditional QTL for FC and FI could be detected at only one stage. Nine conditional and nine unconditional QTL for FC and FI were detected in the earlier three stages while three and two unconditional QTL for FC and ...