Conservation of the PBL-RBOH immune module in land plants.

The rapid production of reactive oxygen species (ROS) is a key signaling output in plant immunity. In the angiosperm model species Arabidopsis thaliana (hereafter Arabidopsis), recognition of non- or altered-self elicitor patterns by cell-surface immune receptors activates the receptor-like cytoplasmic kinases (RLCKs) of the AVRPPHB SUSCEPTIBLE 1 (PBS1)-like (PBL) family, particularly BOTRYTIS-INDUCED KINASE1 (BIK1).1,2,3 BIK1/PBLs in turn phosphorylate the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD) to induce apoplastic ROS production.4,5 PBL and RBOH functions in plant immunity have been extensively characterized in flowering plants. Much less is known about the conservation of pattern-triggered ROS signaling pathways in non-flowering plants. In this study, we show that in the liverwort Marchantia polymorpha (hereafter Marchantia), single members of the RBOH and PBL families, namely MpRBOH1 and MpPBLa, are required for chitin-induced ROS production. MpPBLa directly interacts with and phosphorylates MpRBOH1 at specific, conserved sites within its cytosolic N terminus, and this phosphorylation is essential for chitin-induced MpRBOH1-mediated ROS production. Collectively, our work reveals the functional conservation of the PBL-RBOH module that controls pattern-triggered ROS production in land plants.

Identification of interacting proteins of Arabidopsis cyclophilin38 (AtCYP38) via multiple screening approaches reveals its possible broad functions in chloroplasts.

AtCYP38, a thylakoid lumen localized immunophilin, is found to be essential for photosystem II assembly and maintenance, but how AtCYP38 functions in chloroplast remains unknown. Based on previous functional studies and its crystal structure, we hypothesize that AtCYP38 should function via binding its targets or cofactors in the thylakoid lumen. To identify potential interacting proteins of AtCYP38, we first adopted ATTED-II and STRING web-tools, and found 12 proteins functionally related to AtCYP38. We then screened a yeast two-hybrid library including an Arabidopsis genome wide cDNA with different domain of AtCYP38, and five thylakoid lumen-localized targets were identified. In order to specifically search interacting proteins of AtCYP38 in the thylakoid lumen, we generated a yeast two-hybrid mini library including the thylakoid lumenal proteins and lumenal fractions of thylakoid membrane proteins, and we obtained six thylakoid membrane proteins and nine thylakoid lumenal proteins as interacting proteins of AtCYP38. The interactions between AtCYP38 and several potential targets were further confirmed via pull-down and co-immunoprecipitation assays. Together, a couple of new potential candidate interacting proteins of AtCYP38 were identified, and the results will lay a foundation for unveiling the regulatory mechanisms in photosynthesis by AtCYP38.

Molecular identification of histone acetyltransferases and deacetylases in lower plant Marchantia polymorpha.

Histone is the core component of nucleosome and modification of amino acid residues on histone tails is one of the most pivotal epigenetic regulatory mechanisms. Histone acetylation or deacetylation is carried out by two groups of proteins: histone acetyltransferases (HATs) or histone deacetylases (HDACs), and has been proven to be tightly linked to regulation of gene expression in animals and vascular plants. The biological functions of HATs and HDACs in non-flowering plants remain largely unknown. We found that there are seven MpHAT genes and twelve MpHDAC genes present in the Marchantia genome, and the comprehensive protein sequence analysis of the HAT and HDAC families was introduced to investigate their potential functions. On the basis of the functional domain analysis, eight MpHATs and twelve MpHDACs contain the conserved functional domains as the defining feature of each family. Phylogenetic trees of all families of MpHATs and MpHDACs along with their homologs from different plant and green algae species were constructed to illustrate evolutionary relationship of HAT and HDAC proteins. We found both SIR2 family and RPD3/HDA1 superfamily possess lower plant-specific proteins indicating the potential unknown functions of HATs and HDACs in Marchantia and other lower plant or algae species. Subcellular localization prediction suggests that MpHATs and MpHDACs are likely functioning in various organelles. Expression analysis shows that all MpHAT and MpHDAC genes are expressed in all tissues with differences at the transcriptional level. In addition, their expression patterns were altered in response to various treatments with plant hormones and environmental stress. We concluded that all MpHATs and MpHDACs are functional proteins in Marchantia and involved in various signaling pathways. Marchantia could have developed a complex histone acetylation epigenetic mechanism to regulate growth and development, as well as responses to environment.

Impacts of Cropping Systems on Aggregates Associated Organic Carbon and Nitrogen in a Semiarid Highland Agroecosystem.

The effect of cropping system on the distribution of organic carbon (OC) and nitrogen (N) in soil aggregates has not been well addressed, which is important for understanding the sequestration of OC and N in agricultural soils. We analyzed the distribution of OC and N associated with soil aggregates in three unfertilized cropping systems in a 27-year field experiment: continuously cropped alfalfa, continuously cropped wheat and a legume-grain rotation. The objectives were to understand the effect of cropping system on the distribution of OC and N in aggregates and to examine the relationships between the changes in OC and N stocks in total soils and in aggregates. The cropping systems increased the stocks of OC and N in total soils (0-40 cm) at mean rates of 15.6 g OC m-2 yr-1 and 1.2 g N m-2 yr-1 relative to a fallow control. The continuous cropping of alfalfa produced the largest increases at the 0-20 cm depth. The OC and N stocks in total soils were significantly correlated with the changes in the >0.053 mm aggregates. 27-year of cropping increased OC stocks in the >0.053 mm size class of aggregates and N stocks in the >0.25 mm size class but decreased OC stocks in the <0.053 mm size class and N stocks in the <0.25 mm size class. The increases in OC and N stocks in these aggregates accounted for 99.5 and 98.7% of the total increases, respectively, in the continuous alfalfa system. The increases in the OC and N stocks associated with the >0.25 mm aggregate size class accounted for more than 97% of the total increases in the continuous wheat and the legume-grain rotation systems. These results suggested that long-term cropping has the potential to sequester OC and N in soils and that the increases in soil OC and N stocks were mainly due to increases associated with aggregates >0.053 mm.