The protein kinases AtMAP3Kε1 and BnMAP3Kε1 are functional homologues of S. pombe cdc7p and may be involved in cell division

We identified an Arabidopsis thaliana gene, AtMAP3Kε1, and a Brassica napus cDNA, BnMAP3Kε1, encoding functional protein serine/threonine kinases closely related to cdc7p and Cdc15p from Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. This is the first report of cdc7-related genes in non-fungal eukaryotes; no such genes have as yet been identified in Metazoans. The B. napus protein is able to partially complement a cdc7 loss of function mutation in S. pombe. RT–PCR and in situ hybridisation revealed that the A. thaliana and B. napus genes are expressed in both the sporophytic and the gametophytic tissues of the respective plant species and revealed further that expression is highest in dividing cells. Moreover, AtMAP3Kε1 gene expression is cell cycle-regulated, with higher expression in G2-M phases. Our results strongly suggest that the plant cdc7p-related protein kinases are involved in a signal transduction pathway similar to the SIN pathway, which positively regulates cytokinesis in S. pombe.This work was mainly supported by a EU grant (SIME project BIOTEC-RTD-CEE PL 960275). The authors also acknowledge the financial support of the MERS and CNRS to UMR 8618, and DGESIG PB98–0678

Abstracts

In order to better understand the developmental processes that govern the formation of somatic embryos in oil palm (Elaeis guineensis Jacq.), we investigated the transcription factor genes expressed during embryogenesis in this species. The AP2/EREBP transcription factor family includes the AP2 subgroup, which contains several proteins that play important roles in plant development. We identified and characterized EgAP2-1, which codes for a protein that contains two AP2 domains similar to those of the transcription factor BABYBOOM (BBM) and more generally AINTEGUMENTA-like (AIL) proteins of the AP2 subgroup. In a similar way to related genes from eudicots, ectopic expression of EgAP2-1 in transgenic Arabidopsis plants alters leaf morphology and enhances regeneration capacity. In oil palm, EgAP2-1 transcripts accumulate to the greatest extent in zygotic embryos. This expression pattern was investigated in more detail by in-situ hybridization, revealing that in both zygotic and somatic embryos, EgAP2-1 expression is concentrated in proliferating tissues associated with the early development of leaf primordia, root initials and provascular tissues. (Résumé d'auteur

Genome-wide association study of a panel of vietnamese rice landraces reveals new QTLs for tolerance to water deficit during the vegetative phase

Background: Drought tolerance is a major challenge in breeding rice for unfavorable environments. In this study, we used a panel of 180 Vietnamese rice landraces genotyped with 21,623 single-nucleotide polymorphism markers to perform a genome-wide association study (GWAS) for different drought response and recovery traits during the vegetative stage. These landraces originate from different geographical locations and are adapted to different agrosystems characterized by contrasted water regimes. Vietnamese landraces are often underrepresented in international panels used for GWAS, but they can contain original genetic determinants related to drought resistance. Results: The panel of 180 rice varieties was phenotyped under greenhouse conditions for several drought-related traits in an experimental design with 3 replicates. Plants were grown in pots for 4 weeks and drought-stressed by stopping irrigation for an additional 4 weeks. Drought sensitivity scores and leaf relative water content were measured throughout the drought stress. The recovery capacity was measured 2 weeks after plant rewatering. Several QTLs associated with these drought tolerance traits were identified by GWAS using a mixed model with control of structure and kinship. The number of detected QTLs consisted of 14 for leaf relative water content, 9 for slope of relative water content, 12 for drought sensitivity score, 3 for recovery ability and 1 for relative crop growth rate. This set of 39 QTLs actually corresponded to a total of 17 different QTLs because 9 were simultaneously associated with two or more traits, which indicates that these common loci may have pleiotropic effects on drought-related traits. No QTL was found in association with the same traits in both the indica and japonica subpanels. The possible candidate genes underlying the quantitative trait loci are reviewed. Conclusions: Some of the identified QTLs contain promising candidate genes with a function related to drought tolerance by osmotic stress adjustment

A class IKNOX gene from the palm species Elaeis guineensis (Arecaceae) is associated with meristem function and a distinct mode of leaf dissection

Class I Knotted-like homeobox (KNOX) transcription factors are important regulators of shoot apical meristem function and leaf morphology by their contribution to dissected leaf development. Palms are of particular interest as they produce dissected leaves generated by a distinct mechanism compared with eudicots. The question addressed here was whether class I KNOX genes might be involved in meristem function and leaf dissection in palms. Here, we characterized the EgKNOX1 gene from oil palm (Elaeis guineensis, Arecaceae) and compared it with available sequences from other plant species using phylogenetic analysis. Gene expression pattern was investigated using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. Functional analysis was carried out by ectopic expression in Arabidopsis and rice. EgKNOX1 was orthologous to STM from Arabidopsis and to OSH1 from rice. It was expressed in the central zone of both vegetative and reproductive meristems. During leaf development, its expression was associated with plications from which the leaflets originate. Different modes of leaf dissection are seen to involve a similar class of genes to control meristematic activities, which govern the production of dissected morphologies