Sphingolipid inhibitor response gene GhMYB86 controls fiber elongation by regulating microtubule arrangement

Although the cell membrane and cytoskeleton play essential roles in cellular morphogenesis,the interaction between the membrane and cytoskeleton is poorly understood.Cotton fibers are extremely elongated single cells,which makes them an ideal model for studying cell development.Here,we used the sphingolipid biosynthesis inhibitor,fumonisin B1(FB1),and found that it effectively suppressed the myeloblastosis(MYB)transcription factor GhMYB86,thereby negatively affecting fiber elongation.A direct target of GhMYB86 is GhTUB7,which encodes the tubulin protein,the major component of the microtubule cytoskeleton.Interestingly,both the overexpression of GhMYB86 and GhTUB7 caused an ectopic microtubule arrangement at the fiber tips,and then leading to shortened fibers.Moreover,we found that GhMBE2 interacted with GhMYB86 and that FB1 and reactive oxygen species induced its transport into the nucleus,thereby enhancing the promotion of GhTUB7 by GhMYB86.Overall,we established a GhMBE2-GhMYB86-GhTUB7 regulation module for fiber elongation and revealed that membrane sphingolipids affect fiber elongation by altering microtubule arrangement.

The bacterial effector AvrRxo1 inhibits vitamin B6 biosynthesis to promote infection in rice

Xanthomonas oryzae pv.oryzicola(Xoc),which causes rice bacterial leaf streak,invades leaves mainly through stomata,which are often closed as a plant immune response against pathogen invasion.How Xoc overcomes stomatal immunity is unclear.Here,we show that the effector protein AvrRxo1,an ATPdependent protease,enhances Xoc virulence and inhibits stomatal immunity by targeting and degrading rice OsPDX1(pyridoxal phosphate synthase),thereby reducing vitamin B6(VB6)levels in rice.VB6 is required for the activity of aldehyde oxidase,which catalyzes the last step of abscisic acid(ABA)biosynthesis,and ABA positively regulates rice stomatal immunity against Xoc.Thus,we provide evidence supporting a model in which a major bacterial pathogen inhibits plant stomatal immunity by directly targeting VB6 biosynthesis and consequently inhibiting the biosynthesis of ABA in guard cells to open stomata.Moreover,AvrRxo1-mediated VB6 targeting also explains the poor nutritional quality,including low VB6 levels,of Xoc-infected rice grains.

The Long-Sought-After Salicylic Acid Receptors

The plant hormone salicylic acid （SA） plays a prominent role in modulating plant immune responses against diverse pathogens. SA also influences other physiological pro- cesses in plants, such as senescence-associated gene expres- sion, basal thermogenesis, and seed germination （Vlot et al., 2009）. Because of the critical role of SA in regulating plant immunity, growth, and development, there has been immense research about SA, which has resulted in the dis- covery of numerous plant genes involved in SA biosynthesis or signal transduction. One of the most notable findings was the identification of NPR1 （non-expressor of pathogen- esis protein 1） （Cao et al., 1994; Delaney et al., 1995）, a gene that encodes a master regulatory protein of SA-dependent defense responses and is a transcriptional co-activator of the TGA clade of bZIP transcription factors （transcription factors that contain basic region/leucine zipper motif）.