Deciphering the roles of leucine-rich repeat receptor-like protein kinases (LRR-RLKs) in response to Fusarium wilt in the Vernicia fordii (Tung tree).

In cultivated grasses, tillering, leaf, and inflorescence architecture, as well as abscission ability, are major agronomical traits. In barley (Hordeum vulgare), maize (Zea mays), rice (Oryza sativa), and brachypodium (Brachypodium distachyon), NOOT-BOP-COCH-LIKE (NBCL) genes are essential regulators of vegetative and reproductive development. Grass species usually possess 2-4 NBCL copies and until now a single study in O. sativa showed that the disruption of all NBCL genes strongly altered O. sativa leaf development. To improve our understanding of the role of NBCL genes in grasses, we extended the study of the two NBCL paralogs BdUNICULME4 (CUL4) and BdLAXATUM-A (LAXA) in the nondomesticated grass B. distachyon. For this, we applied reversed genetics and generated original B. distachyon single and double nbcl mutants by clustered regularly interspaced short palindromic repeats - CRISPR associated protein 9 (CRISPR-Cas9) approaches and genetic crossing between nbcl targeting induced local lesions in genomes (TILLING) mutants. Through the study of original single laxa CRISPR-Cas9 null alleles, we validated functions previously proposed for LAXA in tillering, leaf patterning, inflorescence, and flower development and also unveiled roles for these genes in seed yield. Furthermore, the characterization of cul4laxa double mutants revealed essential functions for nbcl genes in B. distachyon development, especially in the regulation of tillering, stem cell elongation and secondary cell wall composition as well as for the transition toward the reproductive phase. Our results also highlight recurrent antagonist interactions between NBCLs occurring in multiple aspects of B. distachyon development.

Brachypodium distachyon UNICULME4 and LAXATUM-A are redundantly required for development.

Unlike rosette leaves, the mature Arabidopsis rosette core can display full resistance to Botrytis cinerea revealing the importance for spatial and developmental aspects of plant fungal resistance. Arabidopsis thaliana is a model host to investigate plant defense against fungi. However, many of the reports investigating Arabidopsis fungal defense against the necrotrophic fungus, Botrytis cinerea, utilize rosette leaves as host tissue. Here we report organ-dependent differences in B. cinerea resistance of Arabidopsis. Although wild-type Arabidopsis rosette leaves mount a jasmonate-dependent defense that slows fungal growth, this defense is incapable of resisting fungal devastation. In contrast, as the fungus spreads through infected leaf petioles towards the plant center, or rosette core, there is a jasmonate- and age-dependent fungal penetration blockage into the rosette core. We report evidence for induced and preformed resistance in the rosette core, as direct rosette core inoculation can also result in resistance, but at a lower penetrance relative to infections that approach the core from infected leaf petioles. The Arabidopsis rosette core displays a distinct transcriptome relative to other plant organs, and BLADE ON PETIOLE (BOP) transcripts are abundant in the rosette core. The BOP genes, with known roles in abscission zone formation, are required for full Arabidopsis rosette core B. cinerea resistance, suggesting a possible role for BOP-dependent modifications that may help to restrict fungal susceptibility of the rosette core. Finally, we demonstrate that cabbage and cauliflower, common Brassicaceae crops, also display leaf susceptibility and rosette core resistance to B. cinerea that can involve leaf abscission. Thus, spatial and developmental aspects of plant host resistance play critical roles in resistance to necrotrophic fungal pathogens and are important to our understanding of plant defense mechanisms.

Michael Huang

Papers

Rosette core fungal resistance in Arabidopsis thaliana