Mechanisms of hormonal regulation of endosperm cap-specific gene expression in tomato seeds.

The micropylar region of endosperm in a seed, which is adjacent to the radicle tip, is called the 'endosperm cap', and is specifically activated before radicle emergence. This activation of the endosperm cap is a widespread phenomenon among species and is a prerequisite for the completion of germination. To understand the mechanisms of endosperm cap-specific gene expression in tomato seeds, GeneChip analysis was performed. The major groups of endosperm cap-enriched genes were pathogenesis-, cell wall-, and hormone-associated genes. The promoter regions of endosperm cap-enriched genes contained DNA motifs recognized by ethylene response factors (ERFs). The tomato ERF1 (TERF1) and its experimentally verified targets were enriched in the endosperm cap, suggesting an involvement of the ethylene response cascade in this process. The known endosperm cap enzyme endo-ß-mannanase is induced by gibberellin (GA), which is thought to be the major hormone inducing endosperm cap-specific genes. The mechanism of endo-ß-mannanase induction by GA was also investigated using isolated, embryoless seeds. Results suggested that GA might act indirectly on the endosperm cap. We propose that endosperm cap activation is caused by the ethylene response of this tissue, as a consequence of mechanosensing of the increase in embryonic growth potential by GA action.

Jasmonic acid and ethylene are involved in the accumulation of osmotin in germinating tomato seeds.

The expression of SlNP24 encoding osmotin was studied in germinating tomato seeds Solanum lycopersicum L. cv. Moneymaker. The results show that the accumulation of the transcripts of SlNP24 and its potential upstream regulator TERF1 encoding an ethylene response factor was induced by ethylene and methyl jasmonate in germinating tomato seeds. There was no effect of gibberellins on the expression of the genes studied. The expression of SlNP24 was localized in the micropylar region of the endosperm of tomato seeds. The promoter of tomato osmotin was active in the endosperm cells of transgenic Arabidopsis thaliana seeds, which contain reporter genes under control of SlNP24 promoter. The activity of SlNP24 promoter in A. thaliana reporter line seeds was visible when the expression of its ortholog gene in A. thaliana (AtOMS34) was observed. The mechanism of induction and a possible role of NP24 in germinating tomato seeds are discussed.

Jasmonates and its mimics differentially elicit systemic defence responses in Nicotiana attenuata.

Coronalon (6-ethyl indanoyl isoleucine), a synthetic jasmonate mimic, is known to regulate levels of transcripts and secondary metabolites that are commonly elicited by methyl jasmonate (MeJA) in a variety of plants. The ability of coronalon and its derivative (In-L-Ile-Me) to elicit MeJA-activated transcriptional and defence responses [nicotine and trypsin proteinase inhibitors (TPIs)] was compared in treated and systemic untreated tissues of wild-type (WT) and NaLOX3-silenced Nicotiana attenuata plants which are unable to activate either local or systemic defence responses. Coronalon and its derivative significantly regulated 71% and 86% of genes up-regulated by MeJA and 53% and 66% of the genes down-regulated by MeJA in the treated leaves, but only 3% and 7% of all regulated genes in untreated, but phylotactically connected, leaves of WT plants. Consistent with their ability to elicit transcriptional responses in treated tissues, coronalon and In-L-Ile-Me increased nicotine and TPIs when applied to the tissues in which these metabolites are produced, namely roots and leaves. However, treating roots elicited TPI activity in leaves in both WT and NaLOX3-silenced plants, suggesting that mimics can be transported apoplastically from roots to leaves in the xylem. This response was lower in NaLOX3-silenced plants, suggesting that the ability of coronalon and In-L-Ile-Me to elicit TPI responses in leaves after root treatments requires intact jasmonic acid (JA) signalling. Treating leaves did not elicit detectable changes in endogenous JA levels but did decrease free salicylic acid contents. It is concluded that coronalon and In-L-Ile-Me elicit jasmonate responses in treated tissues and could be valuable tools for dissecting local and systemic jasmonate signalling networks in plants.

Dehydration induces expression of GALACTINOL SYNTHASE and RAFFINOSE SYNTHASE in seedlings of pea (Pisum sativum L.).

The exposition of 7-day-old pea seedlings to dehydration induced sudden changes in the concentration of monosaccharides and sucrose in epicotyl and roots tissues. During 24h of dehydration, the concentration of glucose and, to a lesser extent, fructose in seedling tissues decreased. The accumulation of sucrose was observed in roots after 4h and in epicotyls after 8h of stress. Epicotyls and roots also began to accumulate galactinol and raffinose after 8h of stress, when small changes in the water content of tissues occurred. The accumulation of galactinol and raffinose progressed parallel to water withdrawal from tissues, but after seedling rehydration both galactosides disappeared. The synthesis of galactinol and raffinose by an early induction (during the first hour of treatment) of galactinol synthase (PsGolS) and raffinose synthase (PsRS) gene expression as well as a later increase in the activity of both enzymes was noted. Signals possibly triggering the induction of PsGolS and PsRS gene expression and accumulation of galactinol and raffinose in seedlings are discussed.

Tissue-printing methods for localization of RNA and proteins that control seed dormancy and germination.

A number of genes and proteins are expressed in a tissue- or cell layer-specific manner. Spatial patterns of gene expression are critical to understanding gene function. Tissue printing provides a simple and rapid method to analyze localization of mRNA and protein at the tissue and cellular levels. This is especially convenient for gene expression analysis in hard tissues, such as seeds that are often difficult to section. Seed RNA or protein can be transferred onto a suitable membrane by printing the cut surface of a bisected seed. This method has been used successfully to determine mRNA and protein localization in seed research. The resolution of printed seed images and RNA and protein signals in tissue printing is sufficient to identify embryo- or endosperm-specific expression of various genes and proteins. In some cases, these studies have contributed to elucidating the spatial characteristics of hydrolytic enzymes putatively involved in the completion of germination and/or early postgerminative growth. By the same principle, tissue-printing methods could also be valuable for elucidating the spatial characteristics of genes/proteins that control the inception, maintenance, and termination of seed dormancy.