Plant Biology Teaching Resources (Higher Education)

(via @SuayibUestuen, thanks!)

The phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) requires type III effector proteins (T3Es) for virulence. After translocation into the host cell, T3Es are thought to interact with components of host immunity to suppress defence responses. XopJ is a T3E protein from Xcv that interferes with plant immune responses; however, its host cellular target is unknown. Here we show that XopJ interacts with the proteasomal subunit RPT6 in yeast andin planta to inhibit proteasome activity. A C235A mutation within the catalytic triad of XopJ as well as a G2A exchange within the N-terminal myristoylation motif abolishes the ability of XopJ to inhibit the proteasome. Xcv ΔxopJ mutants are impaired in growth and display accelerated symptom development including tissue necrosis on susceptible pepper leaves. Application of the proteasome inhibitor MG132 restored the ability of the Xcv ΔxopJ to attenuate the development of leaf necrosis. The XopJ dependent delay of tissue degeneration correlates with reduced levels of salicylic acid (SA) and changes in defence- and senescence-associated gene expression. Necrosis upon infection with Xcv ΔxopJ was greatly reduced in pepper plants with reduced expression of NPR1, a central regulator of SA responses, demonstrating the involvement of SA-signalling in the development of XopJ dependent phenotypes. Our results suggest that XopJ-mediated inhibition of the proteasome interferes with SA-dependent defence response to attenuate onset of necrosis and to alter host transcription. A central role of the proteasome in plant defence is discussed.

Successful sexual reproduction in animals and plants requires communication between male and female gametes. In flowering plants, unlike in animals, eggs and sperm cells are enclosed in multicellular embryo sacs and pollen grains, respectively [1]; guided growth of the pollen tube into the ovule is necessary for fertilization [2]. Pollen tube guidance requires accurate perception of ovule-emitted guidance cues by the receptors in pollen tubes [2, 3 and 4]. Although several ovule-secreted peptides controlling pollen tube guidance have recently been identified, i.e., maize EGG APPARATUS1 (EA1) [5], Torenia LURE1/LURE2 [6], and Arabidopsis CRP810_1/AtLURE1 [7], little is known about the receptors. Here, we identified two receptor-like kinase (RLK) genes preferentially expressed in Arabidopsis pollen tubes, Lost In Pollen tube guidance 1 (LIP1) and 2 (LIP2), which are involved in guidance control of pollen tubes. LIP1 and LIP2 were anchored to the membrane in the pollen tube tip region via palmitoylation, which was essential for their guidance control. Simultaneous inactivation of LIP1 and LIP2 led to impaired pollen tube guidance into micropyle and significantly reduced attraction of pollen tubes toward AtLURE1 [7]. Our results suggest that LIP1 and LIP2 represent essential components of the pollen tube receptor complex to perceive the female signal AtLURE1 for micropylar pollen tube guidance.

Cortical domains are often specified by the local accumulation of active GTPases. Such domains can arise through spontaneous symmetry-breaking, suggesting that GTPase accumulation occurs via positive feedback. Here, we focus on recent advances in fungal and plant cell models – where new work suggests that polarity-controlling GTPases develop only one ‘front’ because GTPase clusters engage in a winner-takes-all competition. However, in some circumstances two or more GTPase domains can coexist, and the basis for the switch from competition to coexistence remains an open question. Polarity GTPases can undergo oscillatory clustering and dispersal, suggesting that these systems contain negative feedback. Negative feedback may prevent polarity clusters from spreading too far, regulate the balance between competition and coexistence, and provide directional flexibility for cells tracking gradients.

Have you ever wondered what makes the colour, taste and smell of strawberries so attractive? Why do the ones you might find growing wild seem tastier? Is there something in the chemistry?