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

Correction par la fertilisation minérale des effets de l'ennoyage sur le blé d'hiver. II. — Expérimentation en culture hydroponique

International audienc

Correction par la fertilisation minérale des effets de l'ennoyage sur le blé d'hiver. I. — Expérimentation sur sol

International audienc

Régulation de l'invertase acide vacuolaire par les stress hydrique chez le maïs (messagers impliqués, effets sur le métabolisme carboné et répercussions sur la répartition des assimilats)

Les invertases catalysent l'hydrolyse irréversible du saccharose en glucose et fructose. Des travaux antérieurs ont montré une augmentation forte et précoce de l'invertase acide vacuolaire, ainsi qu'une accumulation parallèle d'hexoses, dans les feuilles de maïs soumis à un stress hydrique modéré. Cette régulation se déroule majoritairement au niveau de l'expression du seul gène ivr2, codant pour l'une des deux invertases vacuolaires. Le but de ce travail a été de déterminer l'origine et la nature du ou des éléments déclencheurs de l'augmentation d'activité invertase, et d'en examiner les conséquences au niveau de la plante entière. Les effets d'une alimentation de feuilles coupées ou de plantules intactes, en acide abscissique (ABA) ou en glucides exogènes, ont été comparés. Toutes les expériences montrent, que l'ABA est un inducteur puissant de l'expression et de l'activité de l'invertase ivr2. Les résultats vis-à-vis du glucose sont moins tranchés, mais il semble que celui-ci puisse être actif en association avec un effet de blessure. Nos résultats suggèrent aussi des interactions entre les voies de signalisation par l'ABA et les hexoses. Finalement, une étude de l'impact du stress hydrique, sur des maïs au stade de remplissage des grains, a été entreprise à l'aide de marquages au 14CO2. L'exportation hors des feuilles sources et l'importation dans les grains, à 0 et 12 jours après pollinisation, ont été suivi. En cas de stress, les proportions de C exporté et importé sont augmentées par unité de C entrant dans la feuille, alors que l'activité et les niveaux de transcrits ivr2 sont accrus dans les feuilles, et réduits dans les grains et les glumes. Cette expression différentielle suggère que les invertases puissent avoir un rôle dans la répartition des assimilats entre les organes sources et puits, différent de celui supposé jusqu'à présent. Leur modulation tendrait alors à compenser les réductions des flux d'assimilats au niveau de la plante entière.Invertases catalyse the irreversible hydrolysis of sucrose into glucose and fructose which confers to them a particular physiological importance in the utilisation of sucrose, the main plant assimilate. Previous work in the laboratory have shown a large and early enhancement of the vacuolar invertase, in parallel with an increase of the hexose content, in maize leaves under a moderate water stress. This regulation apparently takes place at the transcript level of only one of the two known genes encoding for vacuolar invertases: ivr2. The aim of this work was to determine the origin and nature of the elements triggering the enhancement of the vacuolar invertase and to examine the consequences at the whole plant level. The effects of providing abscisic acid (ABA) ys. soluble carbohydrate to excised source leaves or to roots of intact plantlets was compared. All experiments demonstrated that ABA is a strong enhancer of the ivr2 transcript expression and of soluble invertase activity. Glucose effect was only significant in association with wounding both at activity and transcript levels. However the results suggest an interaction between ABA and hexose signalling pathways. Finally, the consequences of Water stress on maize plants at the grain filling stage was analysed by 14CO2 labelling. Measurement of C export out of source leaves and C import into grains at 0 and 12 days after pollination was performed. Water stress conditions increased the proportion of carbon export and of carbon import when it is expressed by units of carbon input, whereas the vacuolar invertase activity and ivr2 transcript level were increased in leaves and decreased in grain and perianth. This differential expression suggests that invertase regulation may have a different role from the one commonly assigned in source-sink relationships. Invertase variations in intact plants may tend to compensate the reduction of both export and import fluxes.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF