No abstract

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In flowering plants, meiocytes develop from subepidermal cells in anthers and ovules. The mechanisms that integrate generegulatory processes with meiotic programs during reproductive development remain poorly characterized. Here, we show that Arabidopsis thaliana plants deficient in ACTIN-RELATED PROTEIN6 (ARP6), a subunit of the SWR1 ATP-dependent chromatinremodeling complex, exhibit defects in prophase I of female meiosis. We found that this meiotic defect is likely due to dysregulated expression of meiotic genes, particularly those involved in meiotic recombination, including DMC1 (DISRUPTED MEIOTIC cDNA1). Analysis of DMC1 expression in arp6 mutant plants indicated that ARP6 inhibits expression of DMC1 in the megasporocyte and surrounding nonsporogeneous ovule cells before meiosis. After cells enter meiosis, however, ARP6 activates DMC1 expression specifically in the megasporocyte even as it continues to inhibit DMC1 expression in the nonsporogenous ovule cells. We further show that deposition of the histone variant H2A.Z, mediated by the SWR1 chromatin-remodeling complex at the DMC1 gene body, requires ARP6. Therefore, ARP6 regulates female meiosis by determining the spatial and temporal patterns of gene expression required for proper meiosis during ovule development.

hande, 1957; Nyquist, 1991). This approach is based on the assumption that both random and systematic Inexpensive estimates of broad-sense heritability (BSH) may be environmental variation within a planting containing a valuable in plant breeding. This research evaluated two methods for estimating BSH with data from stands of equidistantly spaced geno-single genotype follows an inverse logarithmic function types. Both methods depend on the assumption that genetic and of the number of individual plants within a plot (x), environmental contributions to plot variance (plot ϭ group of contiguwhere a plot is a group of contiguous plants (Smith, ous plants) change at different rates as plot size changes if genetic 1936). Given a measure of environmental variation on variation is distributed randomly. For the method proposed by V.J. an individual basis (V 1), Smith (1936) showed that the Shrikhande, variances among plot means are computed and leastpattern of environmental variation on a plot mean basis squares regression used to estimate environmental and genetic vari-(V x) in such a planting could be represented by the ances and the change in a plot variance with changes in plot size. The regression coefficient b (termed the heterogeneity coefother method involves the same approach, but uses a two-parameter ficient) of the function (Smith's Law): model suggested by G.H. Freeman but not previously used to estimate BSH. Both methods produce biased BSH estimates since genotypic and genotypic ϫ environmental components of variation are insepara-V x ϭ V 1 x b [1] ble. Our objectives were to: (i) develop software to calculate variances for the methods, and (ii) compare BSH estimates generated using In a planting where environmental variation changes these methods with each other and with those from analysis of variance abruptly, phenotypic correlations between neighboring (ANOVA) of data from families grown in the same environment. plants and mean plot variance would decrease rapidly Data were from a perennial herb, Sphaeralcea emoryi Torr. grown as plot size increases and b approaches zero. More conin Tucson, AZ. Shrikhande's method produced parameter estimates sistent environmental effects would be associated with with large variances and BSH estimates that averaged 3.6 times larger a more gradual decline in plot variance and b values than those from Freeman's method. Only BSH estimates from Freeapproaching one. man's method agreed well with those from ANOVA for most traits. Freeman's method may be useful for rapidly and inexpensively gener