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Genetic Mapping Identifies Consistent Quantitative Trait Loci for Yield Traits of Rice under Greenhouse Drought ConditionsImproving drought resistance in crops is imperative under the prevailing erratic rainfall patterns. Drought affects the growth and yield of most modern rice varieties. Recent breeding efforts aim to incorporate drought resistance traits in rice varieties that can be suitable under alternative irrigation schemes, such as in a (semi)aerobic system, as row (furrow-irrigated) rice. The identification of quantitative trait loci (QTLs) controlling grain yield, the most important trait with high selection efficiency, can lead to the identification of markers to facilitate marker-assisted breeding of drought-resistant rice. Here, we report grain yield QTLs under greenhouse drought using an F2:3 population derived from Cocodrie (drought sensitive) × Nagina 22 (N22) (drought tolerant). Eight QTLs were identified for yield traits under drought. Grain yield QTL under drought on chromosome 1 (phenotypic variance explained (PVE) = 11.15%) co-localized with the only QTL for panicle number (PVE = 37.7%). The drought-tolerant parent N22 contributed the favorable alleles for all QTLs except qGN3.2 and qGN5.1 for grain number per panicle. Stress-responsive transcription factors, such as ethylene response factor, WD40 domain protein, zinc finger protein, and genes involved in lipid/sugar metabolism were linked to the QTLs, suggesting their possible role in drought tolerance mechanism of N22 inmore »
The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (
Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors, the authentic histidine phosphotransfer proteins (AHPs) and type‐B response regulators (RRs). Two negative regulators of cytokinin signaling have been identified: the type‐A RRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the rice PHPgenes. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPsfail to complement an Arabidopsis phpmutant ( aphp1/ahp6). Disruption of the three rice PHPsresults in a molecular phenotype consistent with these elements acting as negative regulators of cytokinin signaling, including the induction of a number of type‐A RR and cytokinin oxidase genes. The triple phpmutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture, and seed fill. In contrast tomore »
An ethylene biosynthesis enzyme controls quantitative variation in maize ear length and kernel yield
Maize ear size and kernel number differ among lines, however, little is known about the molecular basis of ear length and its impact on kernel number. Here, we characterize a quantitative trait locus,
qEL7, to identify a maize gene controlling ear length, flower number and fertility. qEL7encodes 1-aminocyclopropane-1- carboxylate oxidase2 (ACO2), a gene that functions in the final step of ethylene biosynthesis and is expressed in specific domains in developing inflorescences. Confirmation of qEL7by gene editing of ZmACO2leads to a reduction in ethylene production in developing ears, and promotes meristem and flower development, resulting in a ~13.4% increase in grain yield per ear in hybrids lines. Our findings suggest that ethylene serves as a key signal in inflorescence development, affecting spikelet number, floral fertility, ear length and kernel number, and also provide a tool to improve grain productivity by optimizing ethylene levels in maize or in other cereals.
A non-destructive approach for measuring rice panicle-level photosynthetic responses using 3D-image reconstruction
Our understanding of the physiological responses of rice inflorescence (panicle) to environmental stresses is limited by the challenge of accurately determining panicle photosynthetic parameters and their impact on grain yield. This is primarily due to the lack of a suitable gas exchange methodology for panicles and non-destructive methods to accurately determine panicle surface area.
To address these challenges, we have developed a custom panicle gas exchange cylinder compatible with the LiCor 6800 Infra-red Gas Analyzer. Accurate surface area measurements were determined using 3D panicle imaging to normalize the panicle-level photosynthetic measurements. We observed differential responses in both panicle and flag leaf for two temperate Japonica rice genotypes (accessions TEJ-1 and TEJ-2) exposed to heat stress during early grain filling. There was a notable divergence in the relative photosynthetic contribution of flag leaf and panicles for the heat-tolerant genotype (TEJ-2) compared to the sensitive genotype (TEJ-1).
The novelty of this method is the non-destructive and accurate determination of panicle area and photosynthetic parameters, enabling researchers to monitor temporal changes in panicle physiology during the reproductive development. The method is useful for panicle-level measurements under diverse environmental stresses and is sensitive enough to evaluate genotypic variation for panicle physiology and architecturemore »
MicroRNAs meet with quantitative trait loci: Small powerful players in regulating quantitative yield traits in rice
MicroRNAs (miRNAs) are small noncoding RNAs which regulate various functions related to growth, development, and stress responses in plants and animals. Rice,
Oryza sativa, is one of the most important food crops of the world. In rice, a number of quantitative trait loci (QTL) controlling yield‐related traits have been identified. Some of them are actually controlled by miRNAs, which control various yield‐related quantitative traits in rice. On one hand, many of these miRNAs are found to regulate more than one yield‐related traits, such as tillering, grain size, and branch number of a panicle. On the other hand, a rice yield‐related trait is usually controlled by multiple miRNAs, for example, grain size being controlled by miR156, miR167, miR396, miR397, and miR1432. In rare case, a single miRNA may specifically regulate only one yield‐related trait, such as, miR444 regulating rice tillering. In this review, we focus on the functions of miRNAs in controlling yield‐related quantitative traits in rice, including panicle grain number, grain weight/size, panicle length and branching, tiller number per plant, spikelet number, seed setting rate, and leaf inclination, and discuss how to modulate the expression of these miRNAs using modern molecular biology tools to promote grain yield.
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