No abstract

Cereal seed development depends on the intimate interaction of filial and maternal tissues, ensuring nourishment of the new generation. The gene jekyll, which was identified in barley (Hordeum vulgare), is preferentially expressed in the nurse tissues. JEKYLL shares partial similarity with the scorpion Cn4 toxin and is toxic when ectopically expressed in Escherichia coli and tobacco (Nicotiana tabacum). In barley, jekyll is upregulated in cells destined for autolysis. The gene generates a gradient of expression in the nucellar projection, which mediates the maternal-filial interaction during seed filling. Downregulation of jekyll by the RNA interference technique in barley decelerates autolysis and cell differentiation within the nurse tissues. Flower development and seed filling are thereby extended, and the nucellar projection no longer functions as the main transport route for assimilates. A slowing down in the proliferation of endosperm nuclei and a severely impaired ability to accumulate starch in the endosperm leads to the formation of irregular and small-sized seeds at maturity. Overall, JEKYLL plays a decisive role in the differentiation of the nucellar projection and drives the programmed cell death necessary for its proper function. We further suggest that cell autolysis during the differentiation of the nucellar projection allows the optimal provision of basic nutrients for biosynthesis in endosperm and embryo.

Ab stractBar ley trans for ma tion me di ated by Agrobacterium tume faciens is rou tinely per formed in a num ber of lab o ra to ries. However, elim i na tion of selectable marker genes and for ma tion of plants ho mo zy gous for the transgene via con ven tional seg rega tion is la bo ri ous and time-con sum ing. Here we sug gest a con cept that in cludes the pro duc tion of pri mary trans gen ic plants via in fec tion of im ma ture em bryos with A. tumefaciens fol lowed by androgenetic gen er a tion of a seg re gat ing pop u lation of en tirely ho mo zy gous plants. Selectable marker-free, true breeding plants car ry ing a sin gle-opy transgene integrant may thus be ef fi ciently and rap idly ob tained. How ever, amenability to Agrobacterium-me di ated trans for ma tion as well as androgenetic po ten tial is ge no type-de pend ent. Ef ficient ge netic trans for ma tion by in fec tion of im ma ture em bryos is so far con fined to the spring type cultivar 'Golden Prom ise' which, how ever, turned out to be re cal ci trant in pol len embryogenesis. To fa cil i tate androgenetic gen er a tion of ho mo zy gous segregants from pri mary transformants, we have es tab lished a method for embryogenic pol len cul ture in cv. Golden Prom ise that in cludes con ven tional cold-treat ment and sub se quent preculture of im ma ture pol len un der star va tion con di tions prior to trans fer to com plete nu tri ent me dium. Fur ther we show that con di tion ing of the pol len cul ture me dium by co-cul ture of im ma ture wheat pis tils as well as ad di tion of pis til-pre con ditioned me dium con sid er ably sup port androgenetic de vel opment. Em ploy ment of the es tab lished method us ing im ma ture pol len of pri mary trans gen ic plants dem on strates that selectable marker-free, true-breed ing trans gen ic prog eny can be rap idly ob tained pur su ing the con cept pro posed. The pro tocol pre sented will be use ful in func tional genomics as well as in mo lec u lar breed ing ap proaches. In tro duc tionSta ble ge netic trans for ma tion is a stan dard method em ployed for the func tional char ac teri sa tion of reg u la tory and pro tein-cod ing nu cleic acid sequences. More over, it of fers a wealth of op por tu nities to con trib ute to crop breed ing. Bar ley is one of the eco nom i cally most im por tant and most widely dis trib uted crop spe cies world wide. Ini tially, di vers trans for ma tion meth ods based upon di rect DNA-trans fer were de vel oped for this spe cies (Wan and Lemaux 1994, Jaehne et al. 1994, Funatsuki et al. 1995, Koprek et al. 1996, Zhang et al. 1999, Holm et al. 2000, how ever, the reproducibility and ef fi ciency of these pro to cols turned out to be rather poor. More over, due to frequent deg ra da tion of the DNA-con structs prior to 591 ACTA PHYSIOLOGIAE PLANTARUM

Small RAC/ROP-family G proteins regulate development and stress responses in plants. Transient overexpression and RNA interference experiments suggested that the barley (Hordeum vulgare) RAC/ROP protein RACB is involved in susceptibility to the powdery mildew fungus Blumeria graminis f. sp. hordei. We created transgenic barley plants expressing the constitutively activated RACB mutant racb-G15V under control of the maize (Zea mays) ubiquitin 1 promoter. Individuals of the T1 generation expressing racb-G15V were significantly more susceptible to B. graminis when compared to segregating individuals that did not express racb-G15V. Additionally, racb-G15V-expressing plants showed delayed shoot development from the third leaf stage on, downward rolled leaves, and stunted roots. Expression of racb-G15V decreased photosynthetic CO 2 -assimilation rates and transpiration of nonstressed leaves. In contrast, racb-G15V-expressing barley leaves, when detached from water supply, showed increased water loss and enhanced transpiration. Water loss was associated with reduced responsiveness to abscisic acid in regard to transpiration when compared to segregants not expressing racb-G15V. Hence, RACB might be a common signaling element in response to both biotic and abiotic stress. (2000) subdivided the 11 Arabidopsis (Arabidopsis thaliana) RAC/ ROP proteins into two major subgroups that can be distinguished by length due to an additional exon in group II. Cereals appear to express six to nine RAC/ ROP genes Schultheiss et al., 2003). Based on the available barley (Hordeum vulgare) transcriptome data, six barley full-length RAC/ROP cDNAs have been isolated, and no further family members could be identified in more than 300,000 expressed sequence tags (Schultheiss et al., 2003). Similar to Arabidopsis RAC/ROPs, barley family members can be subdivided into group I and group II RAC/ ROPs by length. Likewise, similar to Arabidopsis, barley RAC/ROPs can be further distinguished into a total of four clades (Schultheiss et al., 2003).Plant susceptibility to biotrophic fungi is little understood (Schulze-Lefert and Panstruga, 2003;Hü ckelhoven, 2005). Successful pathogens target host proteins to bypass or to suppress basic defense mechanisms. Seemingly, such target proteins are essential to the host because resistant mutants often show pleiotropic growth or cell death phenotypes (Vogel and Somerville, 2000 Article, publication date, and citation information can be found at www.plantphysiol.org/cgi