RESUMO
BACKGROUND: 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. RESULTS: 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 Rab17 and Rab28 genes as well as the late embryogenesis abundant Emb5 and aquaporin genes were related to desiccation rate and parental allele effect. Database searches led to the identification and mapping of two zeaxanthin epoxidase (ZEP) and five novel 9-cis-epoxycarotenoid dioxygenase (NCED) 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. CONCLUSIONS: 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 NCED gene family and another maize ZEP gene were identified and mapped. Among all the identified candidates, aquaporins and members of the Responsive to ABA gene family appeared better candidates than NCEDs and ZEPs.
Assuntos
Ácido Abscísico/biossíntese , Dessecação , Locos de Características Quantitativas , Zea mays/genética , Mapeamento Cromossômico , Endosperma/genética , Endosperma/metabolismo , Perfilação da Expressão Gênica , Genes de Plantas , Família Multigênica , Filogenia , RNA de Plantas/genética , Alinhamento de Sequência , Água/metabolismo , Zea mays/embriologia , Zea mays/metabolismoRESUMO
Indoor mould growth can affect health, especially in early childhood. As part of a birth cohort follow-up, the purpose of this study was firstly to examine spectrum and levels of airborne fungi in 190 Paris newborns' dwellings, and secondly to identify predictors of these levels. Sequential duplicate air samples were collected twice a year in the newborn's bedroom and outside the building. A single-stage multi-holed impactor (Air Ideal) was used with chloramphenicol/MEA agar. Housing characteristics were assessed using a questionnaire administered by a trained interviewer. Cladosporium and Penicillium were isolated in, respectively, 77% and 93% of homes in the cold season, and in 95% and 83% of homes in the hot season. Aspergillus and Alternaria were recovered from indoor air in, respectively, 60% and less than 20% of homes. Geometric means (geometric standard deviation) of indoor total airborne fungal concentrations at two different visits were, respectively, 232.4 (3.2) and 186.7 (2.7)cfu/m(3). In the GEE multivariate analysis, outdoor fungal concentrations were the best predictors for variability of indoor total fungal and Cladosporium concentrations (respectively, R(2)=32% and 31%). Levels of total airborne fungal and Cladosporium concentrations were significantly higher during the hot season (respectively, p=0.003 and p<0.001) and were positively correlated with the duration of bedroom aeration (respectively, p=0.004 and p<0.001). Signs of dampness were associated with higher total airborne fungi (p=0.031) and Aspergillus levels (p=0.055). This study provides for the first time indoor airborne fungal spectrum and concentrations in Paris. Outdoor levels and season largely contributed to the variability of indoor total airborne fungal concentrations, which also depended on aeration and signs of dampness.
