Growth Of Transgenic Lines Research Articles

Regulatory circuits involving bud dormancy factor PpeDAM6

DORMANCY-ASSOCIATED MADS-BOX (DAM) genes have recently emerged as key potential regulators of the dormancy cycle and climate adaptation in perennial species. Particularly, PpeDAM6 has been proposed to act as a major repressor of bud dormancy release and bud break in peach (Prunus persica). PpeDAM6 expression is downregulated concomitantly with the perception of a given genotype-dependent accumulation of winter chilling time, and the coincident enrichment in H3K27me3 chromatin modification at a specific genomic region. We have identified three peach BASIC PENTACYSTEINE PROTEINs (PpeBPCs) interacting with two GA-repeat motifs present in this H3K27me3-enriched region. Moreover, PpeBPC1 represses PpeDAM6 promoter activity by transient expression experiments. On the other hand, the heterologous overexpression of PpeDAM6 in European plum (Prunus domestica) alters plant vegetative growth, resulting in dwarf plants tending toward shoot meristem collapse. These alterations in vegetative growth of transgenic lines associate with impaired hormone homeostasis due to the modulation of genes involved in jasmonic acid, cytokinin, abscisic acid, and gibberellin pathways, and the downregulation of shoot meristem factors, specifically in transgenic leaf and apical tissues. The expression of many of these genes is also modified in flower buds of peach concomitantly with PpeDAM6 downregulation, which suggests a role of hormone homeostasis mechanisms in PpeDAM6-dependent maintenance of floral bud dormancy and growth repression.

Altered Expression of the Malate-Permeable Anion Channel OsALMT4 Reduces the Growth of Rice Under Low Radiance.

We examined the function of OsALMT4 in rice (Oryza sativa L.) which is a member of the aluminum-activated malate transporter family. Previous studies showed that OsALMT4 localizes to the plasma membrane and that expression in transgenic rice lines results in a constitutive release of malate from the roots. Here, we show that OsALMT4 is expressed widely in roots, shoots, flowers, and grain but not guard cells. Expression was also affected by ionic and osmotic stress, light and to the hormones ABA, IAA, and salicylic acid. Malate efflux from the transgenic plants over-expressing OsALMT4 was inhibited by niflumate and salicylic acid. Growth of transgenic lines with either increased OsALMT4 expression or reduced expression was measured in different environments. Light intensity caused significant differences in growth between the transgenic lines and controls. When day-time light was reduced from 700 to 300 μmol m-2s-1 independent transgenic lines with either increased or decreased OsALMT4 expression accumulated less biomass compared to their null controls. This response was not associated with differences in photosynthetic capacity, stomatal conductance or sugar concentrations in tissues. We propose that by disrupting malate fluxes across the plasma membrane carbon partitioning and perhaps signaling are affected which compromises growth under low light. We conclude that OsALMT4 is expressed widely in rice and facilitates malate efflux from different cell types. Altering OsALMT4 expression compromises growth in low-light environments.

Phyllotaxy

Phyllotaxy, the arrangement of organs along the stem, has puzzled scientists for centuries. The shoot apical meristem plays a crucial role in the formation of this pattern, by initiating organ primordia on its flanks in a temporally and spatially controlled manner. Recent studies have shown that primordium position at the meristem is governed by local auxin gradients, but little is known about the subsequent events leading to the phyllotaxy along the mature stem. In a recent report we showed that deviation from the initial phyllotaxy set-up in the meristem is generated during stem growth of transgenic lines affected in miR164-mediated regulation of CUC2 and, to a smaller extent, of wild-type Arabidopsis. This underlines the requirement of maintaining the pattern initiated at the meristem during stem development. In this addendum, we discuss the importance of this mechanism in different mutants and at different stages of Arabidopsis development.

Chitinases of Trichoderma atroviride Induce Scab Resistance and Some Metabolic Changes in Two Cultivars of Apple

ABSTRACT This study reports the combination of a transgene-mediated defense mechanism with a conventionally bred resistance in order to improve apple scab resistance. Two cultivars of apple (Galaxy, scab-susceptible, and Ariane, carrying the Vf resistance gene) were transformed with endochitinase and exochitinase genes derived from the biocontrol fungus Trichoderma atroviride. The obtained transgenic lines were analyzed for the expression of both genes and resistance to two races of the pathogen Venturia inaequalis: the common race 1 and race 6 which overcomes the resistance conferred by the Vf gene. A negative correlation between growth of transgenic lines and endochitinase activity was observed. Reduced growth appeared to be associated with high lignin content and high peroxidase as well as glucanase activity, suggesting that endochitinase activity may disturb the metabolism of the plant. Scab inoculation with races 1 and 6 performed in a growth chamber on 14 lines of normal vigor identified 6 lines with significantly enhanced resistance. Ten lines with reduced vigor were tested in vitro with a bioassay on rooted shoots. All lines expressing high endochitinase activity exhibited a significant reduction of scab symptoms.