Assessment of the individual and combined effects of Rht8 and Ppd-D1a on plant height, time to heading and yield traits in common wheat

Grain yield in cereal crops is a complex trait controlled by multiple genes and influenced by developmental processes and environment. Here we report the effects of alleles Rht8 and Ppd-D1 a on plant height, time to heading, and grain yield and its component traits. Association analysis and quantitative trait locus mapping using phenotypic data from 15 environments led to the following conclusions. First, both Rht8 and Ppd-D1 a reduce plant height. However, Ppd-D1 a but not Rht8 causes earlier heading.Second, both Rht8 and Ppd-D1 a promote grain yield and affect component traits. Their combined effects are substantially larger than those conferred by either allele alone.Third, promotion of grain yield by Rht8 and Ppd-D1 a is through increasing fertile spikelet number. We speculate that Rht8 and Ppd-D1 a act independently and additively in control of plant height, grain yield and yield component. Combination of the two alleles is desirable for adjusting plant height and enhancing grain yield and abiotic stress tolerance.

Transgenic expression of MYB15 confers enhanced sensitivity to abscisic acid and improved drought tolerance in Arabidopsis thaliana

Abiotic stresses cause serious crop losses. Knowledge on genes functioning in plant responses to adverse growth conditions is essential for developing stress tolerant crops. Here we report that transgenic expression of MYB15, encoding a R2R3 MYB transcription factor in Arabidopsis thaliana, conferred hypersensitivity to exogenous abscisic acid （ABA） and improved tolerance to drought and salt stresses. The promoter of MYB15 was active in not only vegetative and reproductive organs but also the guard cells of stomata. Its transcript level was substantially upregulated by ABA, drought or salt treatments. Compared with wild type （WT） control, MYB15 overexpression lines were hypersensitive to ABA in germination assays, more susceptible to ABA-elicited inhibition of root elongation, and more sensitive to ABA-induced stomatal closure. In line with the above findings, the transcript levels of ABA biosynthesis （ABA1, ABA2）, signaling （AB13） and responsive genes （AtADH1, RD22, RD29B, AtEM6） were generally higher in MYB15 overexpression seedlings than in WT controls after treatment with ABA. MYB15 overexpression lines displayed improved survival and reduced water loss rates than WT control under water deficiency conditions. These overexpression lines also displayed higher tolerance to NaCI stress. Collectively, our data suggest that overexpression of MYB15 improves drought and salt tolerance in Arabidopsis possibly by enhancing the expression levels of the genes involved in ABA biosynthesis and signaling, and those encoding the stress-protective proteins.

Molecular and Functional Characterization of Sphingosine-1-Phosphate Lyase Homolog from Higher Plants

Sphingosine-1-phosphate lyase （SPL） is involved in degrading the conserved sphingolipid signaling molecule sphingosine-1-phosphate. However, molecular studies on plant SPL have not been reported to date. Here, we present bioinformatic, molecular and functional analyses of putative SPL proteins from Arabidopsis thaliana and rice （designated as AtSPL and OsSPL, respectively）. Amino acid sequence comparison revealed that plant SPL contalned the pyridoxal-dependent decarboxylase domain and the conserved residue that may be involved in substrate catalysis. When expressed in Saccharomyces cerevisiae, AtSPL and OsSPL corrected the hypersensitive phenotype of the yeast dpl1 deletion strain, which is deficient in endogenous SPL activity, to exogenous supplied sphingolipid long chain bases （LCBs）, suggesting that plant SPL protein is functional In vivo in degrading phosphorylated LCBs. In Arabidopsis, AtSPL transcripts were detected in roots, stems, leaves, flowers and siliques. In pAtSPL-AtSPL∷GUS transgenic lines, the AtSPL∷GUS fusion protein was found in a variety of vegetative and reproductive tissues. AtSPL expression level was dynamically regulated during leaf development and senescence, and was steadily and significantly increased in Arabidopsis seedlings treated with the cell death-inducing fungal toxin fumonisin B1. The potential function of SPL in Arabidopsis is discussed.

Genetic Analysis of Chromosomal Loci Affecting the Content of Insoluble Glutenin in Common Wheat

In common wheat, insoluble glutenin （IG） is an important fraction of flour glutenin macropolymers, and insoluble glutenin content （IGC） is positively associated with key end-use quality parameters. Here, we present a genetic analysis of the chromosomal loci affecting IGC with the data collected from 90 common wheat varieties cultivated in four environments. Statistical analysis showed that IGC was controlled mainly genetically and influenced by the environment. Among the major genetic components known to affect end-use quality, 1BL/1RS translocation had a significantly negative effect on IGC across all four environments. As to the different alleles of Glu-A1, -B1 and -D1 loci, Glu-Ala, Glu-Blb and Glu-Dld exhibited relatively strong positive effects on IGC in all environments. To identify new loci affecting IGC, association mapping with 1355 DArT markers was conducted. A total of 133 markers were found associated with IGC in two or more environments （P 〈 0.05）, ten of which consistently affected IGC in all four environments. The phenotypic variance explained by the ten markers varied from 4.66% to 8.03%, and their elite alleles performed significantly better than the inferior counterparts in enhancing IGC. Among the ten markers, wPt-3743 and wPt-733835 reflected the action of Glu-D1, and wPt-664972 probably indicated the effect of GIu-A1. The other seven markers, forming three clusters on 2AL. 3BL or 7BL chromosome arms, represented newly identified genetic determinants of IGC. Our work provided novel insights into the genetic control of IGC, which may facilitate wheat end- use quality improvement through molecular breeding in the future.

Overexpressing HRS1 Confers Hypersensitivity to Low Phosphate-Elicited Inhibition of Primary Root Growth in Arabidopsis thaliana

Phosphate （Pi） deficiency causes dramatic root system architecture （RSA） changes in higher plants. Here we report that overexpression of HRS1 leads to enhanced sensitivity to low Pi-elicited inhibition of primary root growth in Arabidopsis thaliana seedlings. Bioinformatic investigations uncovered that HRS1 and its six homologs encode putative G2-like transcription factors in Arabidopsis. Analysis of promoter：：GUS reporter lines revealed that HRS1 transcripts were present mainly in the root hair region and root hair cells under Pi-sufficient conditions. Pi deprivation increased HRS1 expression level and expanded its expression domain. Although HRS1 knockout mutant did not differ from wild type （WT） control irrespective of Pi status, its overexpression lines were significantly more susceptible to low Pi-elicited primary root shortening. In both WT and HRS1 overexpression seedlings, low Pi-induced primary root shortening was accompanied by enhanced root hair cell differentiation, but this enhancement occurred to a greater extent in the latter genotype. Collectively, our data suggest that HRS1 may be involved in the modulation of primary root and root hair growth in Pi-deprived Arabidopsis seedlings, and provide useful clues for further research into the function of HRS1 and its homologs and the mechanisms behind RSA changes under Pi-deficient conditions.