In silico analysis of 3 expansin gene promoters reveals 2 hubs controlling light and cytokinins response during bud outgrowth

Bud outgrowth is under the intricate control of environmental and endogenous factors. In a recent paper, ¹ we demonstrated that light perceived by Rosa buds triggers cytokinins (CK) synthesis within 3 hours in the adjacent node followed by their transport to the bud. There, CK control expression of a set of major genes (strigolactones-, auxin-, sugar sink strength-, cells division and elongation-related genes) leading to bud outgrowth in light. Conversely, under dark condition, CK accumulation and transport to the bud are repressed and no bud outgrowth occurs. In this paper, we show that the 3 expansin genes RhEXPA1,2,3 are under the control of both light and CK during bud outgrowth. In silico analysis of promoter sequences highlights 2 regions enriched in light and CK cis-regulatory elements as well as a specific cis-element in pRhEXPA3, potentially responsible for the expression patterns observed in response to CK and light.

Cytokinins Are Initial Targets of Light in the Control of Bud Outgrowth

Bud outgrowth is controlled by environmental and endogenous factors. Through the use of the photosynthesis inhibitor norflurazon and of masking experiments, evidence is given here that light acts mainly as a morphogenic signal in the triggering of bud outgrowth and that initial steps in the light signaling pathway involve cytokinins (CKs). Indeed, in rose (Rosa hybrida), inhibition of bud outgrowth by darkness is suppressed solely by the application of CKs. In contrast, application of sugars has a limited effect. Exposure of plants to white light (WL) induces a rapid (after 3-6 h of WL exposure) up-regulation of CK synthesis (RhIPT3 and RhIPT5), of CK activation (RhLOG8), and of CK putative transporter RhPUP5 genes and to the repression of the CK degradation RhCKX1 gene in the node. This leads to the accumulation of CKs in the node within 6 h and in the bud at 24 h and to the triggering of bud outgrowth. Molecular analysis of genes involved in major mechanisms of bud outgrowth (strigolactone signaling [RwMAX2], metabolism and transport of auxin [RhPIN1, RhYUC1, and RhTAR1], regulation of sugar sink strength [RhVI, RhSUSY, RhSUC2, and RhSWEET10], and cell division and expansion [RhEXP and RhPCNA]) reveal that, when supplied in darkness, CKs up-regulate their expression as rapidly and as intensely as WL Additionally, up-regulation of CKs by WL promotes xylem flux toward the bud, as evidenced by Methylene Blue accumulation in the bud after CK treatment in the dark. Altogether, these results suggest that CKs are initial components of the light signaling pathway that controls the initiation of bud outgrowth.

Mechanosensitive channels: feeling tension in a world under pressure

Plants, like other organisms, are facing multiple mechanical constraints generated both in their tissues and by the surrounding environments. They need to sense and adapt to these forces throughout their lifetimes. To do so, different mechanisms devoted to force transduction have emerged. Here we focus on fascinating proteins: the mechanosensitive (MS) channels. Mechanosensing in plants has been described for centuries but the molecular identification of MS channels occurred only recently. This review is aimed at plant biologists and plant biomechanists who want to be introduced to MS channel identity, how they work and what they might do in planta? In this review, electrophysiological properties, regulations, and functions of well-characterized MS channels belonging to bacteria and animals are compared with those of plants. Common and specific properties are discussed. We deduce which tools and concepts from animal and bacterial fields could be helpful for improving our understanding of plant mechanotransduction. MS channels embedded in their plasma membrane are sandwiched between the cell wall and the cytoskeleton. The consequences of this peculiar situation are analyzed and discussed. We also stress how important it is to probe mechanical forces at cellular and subcellular levels in planta in order to reveal the intimate relationship linking the membrane with MS channel activity. Finally we will propose new tracks to help to reveal their physiological functions at tissue and plant levels.

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida'Radrazz' and Rosa chinensis'Old Blush', cultivated under two light qualities. Plants were grown from one-node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO(2) assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO(2) concentrations. In 'Radrazz', the reduction in CO(2) assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses.

Sugars are under light control during bud burst in Rosa sp

Bud burst in certain species is conditioned by the luminous environment. With roses, the requirement for light is absolute, and darkness totally inhibits bud burst. Few studies have looked into understanding the action of light on the physiological bud burst processes. Here, we show the impact of light on certain components of glucidic metabolism during bud burst. Measurements were taken on decapitated plants of Rosa hybrida L. 'Radrazz' exposed either to darkness, white, blue or R light. Results show that a mobilization of bud and the carrying stem sucrose reserves only takes place in light and accompanies the bud burst. Furthermore, the activity of the RhVI vacuolar acid invertase which contributes to the breakdown of sucrose in the buds, as well as the transcription of the RhVI gene, is reduced in darkness, although it is strongly stimulated by light. The same analysis concerning the RhNAD-SDH gene, coding an NAD-dependent sorbitol dehydrogenase, shows, on the contrary, a strong induction of its transcription in darkness that could reflect the use of survival mechanisms in this condition.

Light controls shoot meristem organogenic activity and leaf primordia growth during bud burst in Rosa sp

Light controls bud burst in many plants, which subsequently affects their architecture. Nevertheless, very little is known about this photomorphogenic process. This study ascertains the effects of light on bud burst and on two of its components, i.e. growth of preformed leaves and meristem organogenesis in six cultivars from three Rosa species (R. hybrida L., R. chinensis L., R. wichurana L.). Defoliated plants were severed above the third basal bud and exposed, either to darkness or to different intensities of white light, to blue, red or to FR, at constant temperature. Bud bursting was inhibited in darkness in the six cultivars of Rosa, but not in Arabidopsis, tomato and poplar plants under the same condition. In all Rosa cultivars, bud burst, growth of preformed leaves and meristem organogenesis were triggered by blue and red lights, and extended by increasing light intensities. FR was inhibitory of bud burst. Partial shading experiments demonstrated that bud and not stem was the active site for light perception in bud burst.

Exogenous application of a lipid transfer protein-jasmonic acid complex induces protection of grapevine towards infection by Botrytis cinerea

Type I plant lipid transfer proteins (LTPs) are small, basic, cystein-rich proteins involved in plant defense mechanisms. Five type I LTPs isoforms, named VvLTP1, 2, 3, 4 and 5 (Vitis vinifera lipid transfer proteins 1-5) were purified to homogeneity from the culture media of 41B grapevine cell suspension. The full sequence of isoforms 1, 3, 4 and 5 could be determined from mass spectrometry measurements of the enzymatically hydrolyzed proteins and from available VvLTP sequences. Phylogenetic analysis revealed that these proteins form two subgroups, one with isoforms 1 and 4, and the second one with isoforms 3 and 5. The ability of the three most abundant ones (VvLTP1, 4 and 3) to interact with jasmonic acid (JA) was tested by fluorometric studies, showing that VvLTP4 was the most efficient to interact with this oxylipin. Exogenous application of the VvLTP4-JA complex on grapevine plantlets induced a high level (80.3+/-10.05%) of tolerance towards Botrytis cinerea, as compared with control plants (18.65+/-12.13%); whereas plants treated with JA or VvLTP4 alone exhibited a lower protection level (31.04+/-9.72% and 45.52+/-7.51% of protection, respectively). The results are discussed in the context of grapevine defense mechanisms.