Abstract. To understand the mechanisms of mRNA transport in eukaryotes, we have isolated Saccharomyces cerevisiae temperature-sensitive (ts) mutants which accumulate poly(A) + RNA ha the nucleus at the restrictive temperature. A total of 21 recessive mutants were isolated and classified into 16 complementation groups. Backcrossed mRNA transportdefective strains from each complementation group have been analyzed. A strain which is ts for heat shock transcription factor was also analyzed since it also shows nuclear accumulation of poly(A) + RNA at 37°C. At 37°C the mRNA of each mutant is characterized by atypically long polyA tails. Unlike ts pre-mRNA splithag mutants, these strains do not interrupt splicing of pre-mRNA at 370C; however four strains accumulate oversized RNA polymerase II transcripts. Some show inhibition of rRNA processing and a further subset of these strains is also characterized by inhibition of tRNA maturation. Several strains accumulate nuclear proteins ha the cytoplasm when incubated at semipermissive temperature. Remarkably, many strains exhibit nucleolar fragmentation or enlargement at the restrictive temperature. Most strains show dramatic ultrastructural alterations of the nucleoplasm or nuclear membrane. Distinct mutants accumulate poly(A) + RNA in characteristic patterns ha the nucleus.

The major maturity gene E1 has the most prominent effect on flowering time and photoperiod sensitivity of soybean, but the pathway mediated by E1 is largely unknown. Here, we found the expression of GmFT4, a homolog of Flowering Locus T, was strongly up-regulated in transgenic soybean overexpressing E1, whereas expression of flowering activators, GmFT2a and GmFT5a, was suppressed. GmFT4 expression was strongly up-regulated by long days exhibiting a diurnal rhythm, but down-regulated by short days. Notably, the basal expression level of GmFT4 was elevated when transferred to continous light, whereas repressed when transferred to continuous dark. GmFT4 was primarily expressed in fully expanded leaves. Transcript abundance of GmFT4 was significantly correlated with that of functional E1, as well as flowering time phenotype in different cultivars. Overexpression of GmFT4 delayed the flowering time in transgenic Arabidopsis. Taken together, we propose that GmFT4 acts downstream of E1 and functions as a flowering repressor, and the balance of two antagonistic factors (GmFT4 vs GmFT2a/5a) determines the flowering time of soybean.

An enormous variety of primary and secondary mRNA structures are compatible with export from the nucleus to the cytoplasm. Therefore, there seems to be a mechanism for RNA export which is independent of sequence recognition. There nevertheless is likely to be some relatively uniform mechanism which allows transcripts to be packaged as ribonucleoprotein particles, to gain access to the periphery of the nucleus and ultimately to translocate across nuclear pores. To study these events, we and others have generated temperature-sensitive recessive mRNA transport (mtr) mutants of Saccharomyces cerevisiae which accumulate poly(A)؉ RNA in the nucleus at 37؇C. Several of the corresponding genes have been cloned. Upon depletion of one of these proteins, Mtr4p, conspicuous amounts of nuclear poly(A)؉ RNA accumulate in association with the nucleolus. Corresponding dense material is also seen by electron microscopy. MTR4 is essential for growth and encodes a novel nuclear protein with a size of ϳ120 kDa. Mtr4p shares characteristic motifs with DEAD-box RNA helicases and associates with RNA. It therefore may well affect RNA conformation. It shows extensive homology to a human predicted gene product and the yeast antiviral protein Ski2p. Critical residues of Mtr4p, including the mtr4-1 point mutation, have been identified. Mtr4p may serve as a chaperone which translocates or normalizes the structure of mRNAs in preparation for export.The mechanism of export of mRNA from the nucleus to the cytoplasm is remarkably accommodating in the sense that an enormous variety of primary and secondary RNA structures are compatible with export. The fact that neither the 5Ј methyl cap structure nor the 3Ј poly(A) tail appears altogether essential for export (16) suggests that there is a mechanism in the nucleus which allows for RNA recognition independent of the sequence. It is likely that during or immediately after their synthesis, transcripts are quickly packaged into ribonucleoprotein particles (RNP) which enable them to gain access to the periphery of the nucleoplasm and interact specifically with components of nuclear pores, through which they subsequently translocate (14,42). If this itinerary is relatively uniform for most mRNAs, it is reasonable to postulate that there are factors which serve as RNA chaperones and/or normalize RNA secondary structure. Single-stranded RNAs spontaneously acquire an extensive secondary structure, which is subject to proteins with annealing activity (p53 and heterogeneous nuclear RNP [hnRNP] A1 [24,25]) and melting activity (helicases [34]). Studies of the yeast Saccharomyces cerevisiae have identified several proteins which, when mutated, lead to nuclear accumulation of poly(A) ϩ RNA without inhibiting pre-mRNA splicing. Apart from nucleoporins (8), these includes components of a nucleocytoplasmic GTPase cycle [the Cnr1/2p (Gsp1/2p) GTPases, Mtr1p (Prp20p), and Rna1p (6, 35)], a cytoplasmic protein (Mtr7p [34a]), the nucleolar protein Mtr3p (19), the nuclear proteins Mtr2p (19) and Rat1p (1), and the ...

The interaction between pathogens and their host plants is a ubiquitous process. Some plant fungal pathogens can form a specific infection structure, such as an appressorium, which is formed by the accumulation of a large amount of glycerin and thereby the creation of an extremely high intracellular turgor pressure, which allows the penetration peg of the appressorium to puncture the leaf cuticle of the host. Previous studies have shown that autophagy energizes the accumulation of pressure by appressoria, which induces its pathogenesis. Similar to other eukaryotic organisms, autophagy processes are highly conserved pathways that play important roles in filamentous fungal pathogenicity. This review aims to demonstrate how the autophagy process affects the pathogenicity of plant pathogens. ARTICLE HISTORY