QTLs and candidate genes for desiccation and abscisic acid content in maize kernels

<p>Abstract</p> <p>Background</p> <p>Kernel moisture at harvest is an important trait since a low value is required to prevent unexpected early germination and ensure seed preservation. It is also well known that early germination occurs in viviparous mutants, which are impaired in abscisic acid (ABA) biosynthesis. To provide some insight into the genetic determinism of kernel desiccation in maize, quantitative trait loci (QTLs) were detected for traits related to kernel moisture and ABA content in both embryo and endosperm during kernel desiccation. In parallel, the expression and mapping of genes involved in kernel desiccation and ABA biosynthesis, were examined to detect candidate genes.</p> <p>Results</p> <p>The use of an intermated recombinant inbred line population allowed for precise QTL mapping. For 29 traits examined in an unreplicated time course trial of days after pollination, a total of 78 QTLs were detected, 43 being related to kernel desiccation, 15 to kernel weight and 20 to ABA content. Multi QTL models explained 35 to 50% of the phenotypic variation for traits related to water status, indicating a large genetic control amenable to breeding. Ten of the 20 loci controlling ABA content colocated with previously detected QTLs controlling water status and ABA content in water stressed leaves. Mapping of candidate genes associated with kernel desiccation and ABA biosynthesis revealed several colocations between genes with putative functions and QTLs. Parallel investigation via RT-PCR experiments showed that the expression patterns of the ABA-responsive <it>Rab17 </it>and <it>Rab28 </it>genes as well as the late embryogenesis abundant <it>Emb5 </it>and aquaporin genes were related to desiccation rate and parental allele effect. Database searches led to the identification and mapping of two <it>zeaxanthin epoxidase </it>(<it>ZEP</it>) and five novel <it>9-cis-epoxycarotenoid dioxygenase </it>(<it>NCED</it>) related genes, both gene families being involved in ABA biosynthesis. The expression of these genes appeared independent in the embryo and endosperm and not correlated with ABA content in either tissue.</p> <p>Conclusions</p> <p>A high resolution QTL map for kernel desiccation and ABA content in embryo and endosperm showed several precise colocations between desiccation and ABA traits. Five new members of the maize <it>NCED </it>gene family and another maize <it>ZEP </it>gene were identified and mapped. Among all the identified candidates, aquaporins and members of the <it>Responsive to ABA </it>gene family appeared better candidates than <it>NCEDs </it>and <it>ZEPs</it>.</p

Water Deficit-Responsive QTLs for Cell Wall Degradability and Composition in Maize at Silage Stage

The use of lignocellulosic biomass for animal feed or biorefinery requires the optimization of its degradability. Moreover, biomass crops need to be better adapted to the changing climate and in particular to periods of drought. Although the negative impact of water deficit on biomass yield has often been mentioned, its impact on biomass quality has only been recently reported in a few species. In the present study, we combined the mapping power of a maize recombinant inbred line population with robust near infrared spectroscopy predictive equations to track the response to water deficit of traits associated with biomass quality. The population was cultivated under two contrasted water regimes over 3 consecutive years in the south of France and harvested at silage stage. We showed that cell wall degradability and β-O-4-linked H lignin subunits were increased in response to water deficit, while lignin and p-coumaric acid contents were reduced. A mixed linear model was fitted to map quantitative trait loci (QTLs) for agronomical and cell wall-related traits. These QTLs were categorized as “constitutive” (QTL with an effect whatever the irrigation condition) or “responsive” (QTL involved in the response to water deficit) QTLs. Fifteen clusters of QTLs encompassed more than two third of the 213 constitutive QTLs and 13 clusters encompassed more than 60% of the 149 responsive QTLs. Interestingly, we showed that only half of the responsive QTLs co-localized with constitutive and yield QTLs, suggesting that specific genetic factors support biomass quality response to water deficit. Overall, our results demonstrate that water deficit favors cell wall degradability and that breeding of varieties that reconcile improved drought-tolerance and biomass degradability is possible

Arabidopsis Sphingosine Kinase and the Effects of Phytosphingosine-1-Phosphate on Stomatal Aperture

Sphingolipids are a major component of membrane lipids and their metabolite sphingosine-1-phosphate (S1P) is a potent lipid mediator in animal cells. Recently, we have shown that the enzyme responsible for S1P production, sphingosine kinase (SphK), is stimulated by the phytohormone abscisic acid in guard cells of Arabidopsis (Arabidopsis thaliana) and that S1P is effective in regulating guard cell turgor. We have now characterized SphK from Arabidopsis leaves. SphK activity was mainly associated with the membrane fraction and phosphorylated predominantly the Δ4-unsaturated long-chain sphingoid bases sphingosine (Sph) and 4,8-sphingadienine, and to a lesser extent, the saturated long-chain sphingoid bases dihydrosphingosine and phytosphingosine (Phyto-Sph). 4-Hydroxy-8-sphingenine, which is a major sphingoid base in complex glycosphingolipids from Arabidopsis leaves, was a relatively poor substrate compared with the corresponding saturated Phyto-Sph. In contrast, mammalian SphK1 efficiently phosphorylated Sph, dihydrosphingosine, and 4,8-sphingadienine, but not the 4-hydroxylated long-chain bases Phyto-Sph and 4-hydroxy-8-sphingenine. Surface dilution kinetic analysis of Arabidopsis SphK with Sph presented in mixed Triton X-100 micelles indicated that SphK associates with the micellar surface and then with the substrate presented on the surface. In addition, measurements of SphK activity under different assay conditions combined with phylogenetic analysis suggest that multiple isoforms of SphK may be expressed in Arabidopsis. Importantly, we found that phytosphingosine-1-phosphate, similar to S1P, regulates stomatal apertures and that its action is impaired in guard cells of Arabidopsis plants harboring T-DNA null mutations in the sole prototypical G-protein α-subunit gene, GPA1

Signaling and sensing: the role of Class II TREHALOSE 6-PHOSPHATE SYNTHASE genes in suppression of eskimo1 dwarfism phenotype.

International audienceIn Arabidopsis, eskimo1 mutant is due to a mutation in XOAT1 gene (Xylan O-acetyl transferase 1). Its mutation leads to abnormal xylan acetylation resulting in collapsed xylem. This cell wall defect reduces water conductivity and generates constitutive plant stress leading to a dwarfism phenotype. This phenotype is supressed by a mutation in Class II TREHALOSE 6-PHOSPHATE SYNTHASE 7 (TPS 7) gene. The two closest homologous class II genes of TPS7, TPS5 and TPS6, were also investigated for esk1 dwarfism suppression. The results will be presented here

Tissue lignification, cell wall <em>p</em>-coumaroylation and degradability of maize stems depend on water status

International audienceWater supply and valorization are two urgent issues in the utilization of maize biomass in the context of climate change and replacement of fossil resources. Maximizing maize biomass valorization is of interest to make biofuel conversion competitive, and to increase forage energetic value for animal fodder. One way to estimate biomass valorization is to quantify cell wall degradability. In this study, we evaluated the impact of water supply on cell wall degradability, cell wall contents and structure, and distribution of lignified cell types in maize internodes using dedicated high-throughput tools to effectively phenotype maize internodes from 11 inbred lines under two contrasting irrigation scenarios in field trials over three years. Overall, our results clearly showed that water deficit induced significant changes in lignin content and distribution along with a reduction in lignin p-coumaroylation, thereby impacting cell wall degradability. Additionally, we also observed that responses to a water deficit vaned between the lines examined, underscoring biochemical and histological target traits for plant breeding

Signaling and sensing: the role of Class II TREHALOSE 6-PHOSPHATE SYNTHASE genes in suppression of eskimo1 dwarfism phenotype.

International audienceIn Arabidopsis, eskimo1 mutant is due to a mutation in XOAT1 gene (Xylan O-acetyl transferase 1). Its mutation leads to abnormal xylan acetylation resulting in collapsed xylem. This cell wall defect reduces water conductivity and generates constitutive plant stress leading to a dwarfism phenotype. This phenotype is supressed by a mutation in Class II TREHALOSE 6-PHOSPHATE SYNTHASE 7 (TPS 7) gene. The two closest homologous class II genes of TPS7, TPS5 and TPS6, were also investigated for esk1 dwarfism suppression. The results will be presented here

Identification de marqueurs génétiques impliqués dans le rendement et la composition de la biomasse lignocellulosique.

International audienc

Transcriptome analysis of a chilling tolerance strategy in European maize dent germplasm.

International audienceMaize has become an extensively cultivated crop in high latitudes like Northern Europe thanks to historical improvements of cold tolerance. However, earlier sowing increase the risk of exposure to longer chilling periods, affecting early growth and frequently plant performance and final yield. Understanding how maize responds to chilling periods is therefore a major task to both better understand maize local adaptation and improve agriculture. Here, we evaluated two sister double-haploid dent maize lines sharing 82% of their genome and displaying a contrasted tolerance to chilling. Using an Illumina stranded and paired-end mRNA-seq dataset from leaves of both sister lines grown under control and chilling conditions, we captured the allelic variation consequences at the transcript level. Clustering of differentially expressed gene profiles let us identify 574 genes differentially expressed, 513 and 61 being up- and down-expressed in the chilling-tolerant line compared to the chilling-sensitive line. We then explored how the variation in gene expression contributes to the variation in phenotypic traits. Genes associated with these traits were identified, paving the way for pinpointing candidate genes for chilling tolerance in future follow-up studies