Molecular characterization of 60 isolated wheat MYB genes and analysis of their expression during abiotic stress

The proteins of the MYB superfamily play central roles in developmental processes and defence responses in plants. Sixty unique wheat MYB genes that contain full-length cDNA sequences were isolated. These 60 genes were grouped into three categories, namely one R1R2R3-MYB, 22 R2R3-MYBs, and 37 MYB-related members. The sequence composition of the R2 and R3 repeats was conserved among the 22 wheat R2R3-MYB proteins. Phylogenetic comparison of the members of this superfamily among wheat, rice, and Arabidopsis revealed that the putative functions of some wheat MYB proteins were clustered into the Arabidopsis functional clades. Tissue-specific expression profiles showed that most of the wheat MYB genes were expressed in all of the tissues examined, suggesting that wheat MYB genes take part in multiple cellular processes. The expression analysis during abiotic stress identified a group of MYB genes that respond to one or more stress treatments. The overexpression of a salt-inducible gene, TaMYB32, enhanced the tolerance to salt stress in transgenic Arabidopsis. This study is the first comprehensive study of the MYB gene family in Triticeae.     

Genetics of flowering time in bread wheat <Emphasis Type="Italic">Triticum aestivum</Emphasis>: complementary interaction between vernalization-insensitive and photoperiod-insensitive mutations imparts very early flowering habit to spring wheat

Time to flowering in the winter growth habit bread wheat is dependent on vernalization (exposure to cold conditions) and exposure to long days (photoperiod). Dominant Vrn-1 (Vrn-A1, Vrn-B1 and Vrn-D1) alleles are associated with vernalization independent spring growth habit. The semidominant Ppd-D1a mutation confers photoperiod-insensitivity or rapid flowering in wheat under short day and long day conditions. The objective of this study was to reveal the nature of interaction between Vrn-1 and Ppd-D1a mutations (active alleles of the respective genes vrn-1 and Ppd-D1b). Twelve Indian spring wheat cultivars and the spring wheat landrace Chinese Spring were characterized for their flowering times by seeding them every month for five years under natural field conditions in New Delhi. Near isogenic Vrn-1 Ppd-D1 and Vrn-1 Ppd-D1a lines constructed in two genetic backgrounds were also phenotyped for flowering time by seeding in two different seasons. The wheat lines of Vrn-A1a Vrn-B1 Vrn-D1 Ppd-D1a, Vrn-A1a Vrn-B1 Ppd-D1a and Vrn-A1a Vrn-D1 Ppd-D1a (or Vrn-1 Ppd-D1a) genotypes flowered several weeks earlier than that of Vrn-A1a Vrn-B1 Vrn-D1 Ppd-D1b, Vrn-A1b Ppd-D1b and Vrn-D1 Ppd-D1b (or Vrn-1 Ppd-D1b) genotypes. The flowering time phenotypes of the isogenic vernalization-insensitive lines confirmed that Ppd-D1a hastened flowering by several weeks. It was concluded that complementary interaction between Vrn-1 and Ppd-D1a active alleles imparted super/very-early flowering habit to spring wheats. The early and late flowering wheat varieties showed differences in flowering time between short day and long day conditions. The flowering time in Vrn-1 Ppd-D1a genotypes was hastened by higher temperatures under long day conditions. The ambient air temperature and photoperiod parameters for flowering in spring wheat were estimated at 25°C and 12 h, respectively.     

Arabidopsis CAPRICE-LIKE MYB 3 (CPL3) controls endoreduplication and flowering development in addition to trichome and root hair formation

CAPRICE (CPC) encodes a small protein with an R3 MYB motif and promotes root hair cell differentiation in Arabidopsis thaliana. Three additional CPC-like MYB genes, TRY (TRIPTYCHON), ETC1 (ENHANCER OF TRY AND CPC 1) and ETC2 (ENHANCER OF TRY AND CPC 2) act in a redundant manner with CPC in trichome and root hair patterning. In this study, we identified an additional homolog, CPC-LIKE MYB 3 (CPL3), which has high sequence similarity to CPC, TRY, ETC1 and ETC2. Overexpression of CPL3 results in the suppression of trichomes and overproduction of root hairs, as has been observed for CPC, TRY, ETC1 and ETC2. Morphological studies with double, triple and quadruple homolog mutants indicate that the CPL3 gene cooperatively regulates epidermal cell differentiation with other CPC homologs. Promoter-GUS analyses indicate that CPL3 is specifically expressed in leaf epidermal cells, including stomate guard cells. Notably, the CPL3 gene has pleiotropic effects on flowering development, epidermal cell size and trichome branching through the regulation of endoreduplication.     

Copy number variation affecting the Photoperiod-B1 and Vernalization-A1 genes is associated with altered flowering time in wheat (Triticum aestivum)

The timing of flowering during the year is an important adaptive character affecting reproductive success in plants and is critical to crop yield. Flowering time has been extensively manipulated in crops such as wheat (Triticum aestivum L.) during domestication, and this enables them to grow productively in a wide range of environments. Several major genes controlling flowering time have been identified in wheat with mutant alleles having sequence changes such as insertions, deletions or point mutations. We investigated genetic variants in commercial varieties of wheat that regulate flowering by altering photoperiod response (Ppd-B1 alleles) or vernalization requirement (Vrn-A1 alleles) and for which no candidate mutation was found within the gene sequence. Genetic and genomic approaches showed that in both cases alleles conferring altered flowering time had an increased copy number of the gene and altered gene expression. Alleles with an increased copy number of Ppd-B1 confer an early flowering day neutral phenotype and have arisen independently at least twice. Plants with an increased copy number of Vrn-A1 have an increased requirement for vernalization so that longer periods of cold are required to potentiate flowering. The results suggest that copy number variation (CNV) plays a significant role in wheat adaptation.     

Flowering time diversification and dispersal in central Eurasian wild wheat Aegilops tauschii Coss.: genealogical and ecological framework

Timing of flowering is a reproductive trait that has significant impact on fitness in plants. In contrast to recent advances in understanding the molecular basis of floral transition, few empirical studies have addressed questions concerning population processes of flowering time diversification within species. We analyzed chloroplast DNA genealogical structure of flowering time variation in central Eurasian wild wheat Aegilops tauschii Coss. using 200 accessions that represent the entire species range. Flowering time measured as days from germination to flowering varied from 144.0 to 190.0 days (average 161.3 days) among accessions in a common garden/greenhouse experiment. Subsequent genealogical and statistical analyses showed that (1) there exist significant longitudinal and latitudinal clines in flowering time at the species level, (2) the early-flowering phenotype evolved in two intraspecific lineages, (3) in Asia, winter temperature was an environmental factor that affected the longitudinal clinal pattern of flowering time variation, and (4) in Transcaucasus-Middle East, some latitudinal factors affected the geographic pattern of flowering time variation. On the basis of palaeoclimatic, biogeographic, and genetic evidence, the northern part of current species' range [which was within the temperate desert vegetation (TDV) zone at the Last Glacial Maximum] is hypothesized to have harbored species refugia. Postglacial southward dispersal from the TDV zone seems to have been driven by lineages that evolved short-flowering-time phenotypes through different genetic mechanisms in Transcaucasus-Middle East and Asia.     

Quantitative trait loci (QTL) mapping of blush skin and flowering time in a European pear (<Emphasis Type="Italic">Pyrus communis</Emphasis>) progeny of ‘Flamingo’ × ‘Abate Fetel’

Blush skin and flowering time are agronomic traits of interest to the Agricultural Research Council (ARC) Infruitec-Nietvoorbij pear breeding programme. The genetic control of these traits was investigated in the pear progeny derived from ‘Flamingo’ (blush cultivar) × ‘Abate Fetel’ (slightly blush) made up of 121 seedlings. Blush skin was scored phenotypically over three seasons and flowering time was scored over two seasons. A total of 160 loci from 137 simple sequence repeat (SSR) markers were scored in the progeny and used to construct parental genetic linkage maps. Quantitative trait loci (QTL) analysis revealed two QTLs for blush skin, a major QTL on linkage group (LG) 5 in ‘Flamingo’, and a major QTL on LG9 in ‘Abate Fetel’. Two SSR markers, NB101a and SAmsCO865954, were closely linked with the major QTL on LG5 in ‘Flamingo’, with alleles 139 bp and 462 bp in coupling, respectively. These markers were present in approximately 90% of the seedlings scored as good blush (class 4) based on the average data set. These two markers were used to genotype other pear accessions to validate the QTL on LG5 with the view of marker-assisted selection. Two candidate genes, MYB86 and UDP-glucosyl transferase, were associated with the QTL on LG5 and MYB21 and MYB39 were associated with the QTL on LG9. QTL analysis for flowering time revealed a major QTL located on LG9 in both parents. Marker GD142 with allele 161 bp from ‘Flamingo’ was present in approximately 88% of the seedlings that flowered earlier than either parent, based on the average data set. The QTLs and linked markers will facilitate marker-assisted selection for the improvement of these complex traits.     

基因芯片分析杀雄剂SQ-1诱导小麦生理型雄性不育的基因差异表达

为揭示小麦生理型雄性不育的分子机理,更好地为小麦杂种优势利用提供理论依据和技术支撑,本研究以SQ-1诱导的西农558生理型雄性不育的花药为试验材料,以未经SQ-1处理的西农558的花药为对照,利用基因芯片技术对两者的基因表达差异进行了分析,并对部分基因运用半定量PCR技术进行了验证.结果表明,在55 052个转录本中, 两材料间差异表达的转录本有2 052条, 其中1 294个基因表达上调,758个基因表达下调.功能分类表明这些基因主要参与了毒性物质响应、逆境响应、多糖代谢及信号转导等重要生命过程.为验证芯片数据的可信性, 利用cDNA半定量 PCR 法对11个差异表达显著的基因(Ta.116, Ta.5629, TaAffx.122333, Ta.30726, Ta.13682, Ta.4057, Ta.4101, Ta.4139, Ta.11957, Ta.25934, Ta.27552) 进行验证.结果证明,无论是上调表达的还是下调表达的基因,其表达模式都与基因芯片的检测结果的一致.这些基因可作为育性相关候选基因开展下一步研究.