Stronger induction of callose deposition in barley by Russian wheat aphid than bird cherry-oat aphid is not associated with differences in callose synthase or ≤-1,3-glucanase expression

The effects of infestation by the bird cherry-oat aphid (BCA), (Rhopalosiphum padi L) and the Russian wheat aphid (RWA) (Diuraphis noxia Mordvilko) on callose deposition and gene expression related to callose accumulation were investigated in barley (Hordeum vulgare L. cv. Clipper). The BCA, which gives no visible symptoms, induced very limited callose deposition, even after 14 days of infestation. In contrast, RWA, which causes chlorosis, white and yellow streaking and leaf rolling, induced callose accumulation already after 24h in longitudinal leaf veins. The deposition was pronounced after 72 h, progressing during 7 and 14 days of infestation. In RWA-infested source leaves, callose was also induced in longitudinal veins basipetal to the aphid-infested tissue, whereas in sink leaves, more callose deposition was found above the feeding sites. Nine putative callose synthase genes were identified in a data base search, of which eight were expressed in the leaves, but with similar level of expression in control and aphid-infested tissue. Four out of 12 examined β-1,3-glucanases were expressed in the leaves, and three of them were up-regulated in aphid-infested tissue. They were all more strongly induced by RWA than BCA. The results suggest that callose accumulation may be partly responsible for the symptoms resulting from RWA feeding and that a callose-inducing signal may be transported in the phloem. Furthermore it is concluded that the absence of callose deposition in BCA-infested leaves is not due to a stronger induction of callose-degrading β-1,3-glucanases in this tissue, as compared to RWA-infested leaves

Novel insights into the action of SHI/STY transcriptional regulators during plant development

One key player in plant organogenesis is the phytohormone auxin, and this thesis reveal that members of the SHI/STY gene family participate in the regulation of auxin homeostasis and organ development in Arabidopsis thaliana. Using inducible constructs, ChIP, and EMSA, we could show that the SHI/STY members act as transcriptional activators directly binding to the promoter of the auxin biosynthesis gene YUC4. Additional putative downstream targets were identified encoding transcription factors, other auxin biosynthesis enzymes and enzymes involved in cell wall modulations. This work also brings novel insight into SHI/STY-dependent regulation of cotyledon and leaf vascular patterning and stamen number. Detailed expression studies of SHI/STY genes and several downstream targets confirm their overlapping spatial and temporal expression pattern during cotyledon, leaf, stamen and gynoecium development, clearly supporting the partially redundant function of the SHI/STY family members during the development of these organs. In addition, the expression of SHI/STY members is partially mediated through a conserved motif in their promoter region, a GCC-box, which appears to be essential for SHI/STY expression in aerial organs. Furthermore, a group of putative upstream regulators belonging to the AP2/ERF family have been identified, which requires the GCC-box for their transcriptional regulation of the SHI/STY genes

Regulation of callose synthases and beta-1,3-glucanases during aphid infestation on barley cv. Clipper

Plant resistance hypothesis says that under a period of time when a plant is exposed to powerful herbivore attack it will prioritise defence as a major metabolic function. In theory, induced plant defence (resistance) will provide opportunities for this organism to “invest” in other functions, in example growth when attackers are absent. One of the compounds taking part in plant defence is callose. This β-1,3-glucan is synthesised by callose synthase and broken down by β-1,3-glucanase. Deposition of callose occurs as a reaction to aphid attack an varies, depending on cultivars, and aphid species. In this experiment barley (Hordeum vulgare) cultivar Clipper is being infested with two types of aphids: Russian wheat aphid (RWA, Diuraphis noxia) and bird cherry-oat aphid (BCA, Rhopalosiphium padi) over a time period. Infestation by those two insects results in different callose formation and deposition level. Six sequences encoding for putative callose synthase genes and nine sequences encoding for β-1,3-glucanase were examined by RT-PCR and Real – Time PCR methods for different expression patterns. The results did not show any significant regulation of gene expression during RWA and BCA attack for any of these genes. Thus the pathway regulating aphid – induced callose deposition in barley reminds unresolved

SHI/STY Genes Affect Pre- and Post-meiotic Anther Processes in Auxin Sensing Domains in Arabidopsis

In flowering plants, mature sperm cells are enclosed in pollen grains formed in structures called anthers. Several cell layers surrounding the central sporogenous cells of the anther are essential for directing the developmental processes that lead to meiosis, pollen formation, and the subsequent pollen release. The specification and function of these tissues are regulated by a large number of genetic factors. Additionally, the plant hormone auxin has previously been shown to play important roles in the later phases of anther development. Using the R2D2 auxin sensor system we here show that auxin is sensed also in the early phases of anther cell layer development, suggesting that spatiotemporal regulation of auxin levels is important for early anther morphogenesis. Members of the SHI/STY transcription factor family acting as direct regulators of YUC auxin biosynthesis genes have previously been demonstrated to affect early anther patterning. Using reporter constructs we show that SHI/STY genes are dynamically active throughout anther development and their expression overlaps with those of three additional downstream targets, PAO5, EOD3 and PGL1. Characterization of anthers carrying mutations in five SHI/STY genes clearly suggests that SHI/STY transcription factors affect anther organ identity. In addition, their activity is important to repress periclinal cell divisions as well as premature entrance into programmed cell death and cell wall lignification, which directly influences the timing of anther dehiscence and the pollen viability. The SHI/STY proteins also prevent premature pollen germination suggesting that they may play a role in the induction or maintenance of pollen dormancy

Expression of Arabidopsis SHORT INTERNODES/STYLISH Family Genes in Auxin Biosynthesis Zones of Aerial Organs Is Dependent on a GCC Box-Like Regulatory Element

Auxin/indole-3-acetic acid (IAA) biosynthesis in Arabidopsis (Arabidopsis thaliana) plays a major role in growth responses to developmental and genetic signals as well as to environmental stimuli. Knowledge of its regulation, however, remains rudimentary, and few proteins acting as transcriptional modulators of auxin biosynthesis have been identified. We have previously shown that alteration in the expression level of the SHORT INTERNODES/STYLISH (SHI/STY) family member STY1 affects IAA biosynthesis rates and IAA levels and that STY1 acts as a transcriptional activator of genes encoding auxin biosynthesis enzymes. Here, we have analyzed the upstream regulation of SHI/STY family members to gain further insight into transcriptional regulation of auxin biosynthesis. We attempted to modulate the normal expression pattern of STY1 by mutating a putative regulatory element, a GCC box, located in the proximal promoter region and conserved in most SHI/STY genes in Arabidopsis. Mutations in the GCC box abolish expression in aerial organs of the adult plant. We also show that induction of the transcriptional activator DORNROSCHEN-LIKE (DRNL) activates the transcription of STY1 and other SHI/STY family members and that this activation is dependent on a functional GCC box. Additionally, STY1 expression in the strong drnl-2 mutant or the drn drnl-1 puchi-1 triple mutant, carrying knockdown mutations in both DRNL and its close paralogue DRN as well as one of their closest homologs, PUCHI, was significantly reduced, suggesting that DRNL regulates STY1 during normal plant development and that several other genes might have redundant functions

The Arabidopsis thaliana STYLISH1 Protein Acts as a Transcriptional Activator Regulating Auxin Biosynthesis[C][W]

Biosynthesis of the plant hormone auxin must be tightly controlled. This work shows that the STYLISH1 protein of the plant species Arabidopsis thaliana plays an important role in this process by directly binding to and activating at least one of the auxin biosynthesis genes