Summary• Signalling by ubiquitination is implicated in diverse aspects of the plant lifecycle, and enzymes of ubiquitin metabolism are overrepresented in the Arabidopsis genome compared with other model eukaryotes. Despite the importance of ubiquitination in the regulation of signalling, little is known about deubiquitinating enzymes, which reverse the process of ubiquitination.• Transgenic RNA interference-based cosuppression and the isolation of Atubp12 ⁄ 13 double mutants collectively provides the first report that AtUBP12 and AtUBP13 are functionally redundant and are required for immunity against virulent Pseudomonas syringae pv tomato in Arabidopsis. The Solanaceous AtUBP12 orthologue NtUBP12 was identified. Viral-induced gene silencing and transient gain-of-function assays were employed to establish that the NtUBP12 protein functions as a negative regulator of the Cf-9-triggered hypersensitive response.• Here, we demonstrate that NtUBP12 and AtUBP12 are bona fide deubiquitinating enzymes capable of cleaving lysine-48-linked ubiquitin chains. AtUBP12 and NtUBP12 are functionally interchangeable and their deubiquitinating activity is required to suppress plant cell death.• Overall, our data implicate AtUBP12-and NtUBP12-dependent deubiquitination in the stabilization of common substrates across Solanaceae and Brassicaceae which regulate disease resistance.
Kiwifruit vines are perennial plants grown in climates varying from maritime to continental. To determine key responses to temperature, vines were heated at different stages of fruit development, and vine growth and fruit composition examined. Heating vines during fruit starch accumulation caused a major shift in partitioning towards vegetative growth and dramatically reduced fruit carbohydrate and vitamin C. In the following season, growth and flowering were severely reduced. Heating vines during fruit cell division had minimal long-term effects, whereas heating during fruit maturation delayed starch degradation and fruit ripening and affected growth in the following season. When vines were removed from heat, fruit dry matter, starch and sugar levels were always reduced but hexose : sucrose ratios and inositol were raised. Heating vines affected expression of two sucrose synthase genes, but this did not correlate with reduction in fruit carbohydrate. Activity and expression of L -galactose dehydrogenase decreased as fruit developed, suggesting some vitamin C biosynthesis must take place in the fruit. Activity and expression of actinidin increased in response to heat. The results of this study have demonstrated both short and longterm plant responses to elevated temperatures in woody perennials, and that the timing of heat exposure has severe consequences for vitamin C levels in fruit.
The photoperiodic response in Arabidopsis thaliana requires the precise regulation of CONSTANS (CO) expression in relation to the light period during the day. In short days (SDs) levels of CO expression are normally low during the light period, and this results in delayed flowering compared with long days (LDs) when CO expression rises to high levels before the end of the light period. We identified a novel flowering time gene called DAY NEUTRAL FLOWERING (DNF) that acts in the same flowering pathway as CO. DNF is a membrane-bound E3 ligase that represses CO expression and plays an important role in maintaining low levels of CO expression in SDs. The effect of DNF on the rhythm of CO expression is essential for the photoperiodic response of Arabidopsis, enabling it to have a different flowering response in LDs and SDs.
Petal development and senescence entails a normally irreversible process. It starts with petal expansion and pigment production, and ends with nutrient remobilization and ultimately cell death. In many species this is accompanied by petal abscission. Post-harvest stress is an important factor in limiting petal longevity in cut flowers and accelerates some of the processes of senescence such as petal wilting and abscission. However, some of the effects of moderate stress in young flowers are reversible with appropriate treatments. Transcriptomic studies have shown that distinct gene sets are expressed during petal development and senescence. Despite this, the overlap in gene expression between developmental and stress-induced senescence in petals has not been fully investigated in any species. Here a custom-made cDNA microarray from Alstroemeria petals was used to investigate the overlap in gene expression between developmental changes (bud to first sign of senescence) and typical post-harvest stress treatments. Young flowers were stressed by cold or ambient temperatures without water followed by a recovery and rehydration period. Stressed flowers were still at the bud stage after stress treatments. Microarray analysis showed that ambient dehydration stress accelerates many of the changes in gene expression patterns that would normally occur during developmental senescence. However, a higher proportion of gene expression changes in response to cold stress were specific to this stimulus and not senescence related. The expression of 21 transcription factors was characterized, showing that overlapping sets of regulatory genes are activated during developmental senescence and by different stresses.
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