Arabidopsis NIMIN1,2 mediate redox homeostasis and JA/ET pathways to modulate Botrytis cinerea resistance

Arabidopsis NIM1-INTERACTING1 (NIMIN1) and NIMIN2 are required for salicylic acid (SA)-dependent resistance against biotrophic pathogens. In this study, we have demonstrated that NIMIN1, 2 are also essential for plant defense response to necrotrophic pathogen Botrytis cinerea. The nimin1 and nimin2 mutants displayed a higher susceptibility against B. cinerea than the wild type, which correlated with a decrease in B. cinerea-induced PDF).2 expression. Mutation in NIMIN1 or NIMIN2 enhanced accumulation of hydrogen peroxide (H_2O_2) with reductions in the activities of three main antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) at the early time (24h) of upon B. cinerea infection. These mutations also resulted in a visible decrease in B.cinerea-induced Ethylene Responsive Factor 1 (ERF1), Octadecanoid-Responsive Arabidopsis AP2/ERF 59 (ORA59), Allene Oxide Cyclase (AOC3), Opda Reductase 3 (OPR3),ACC Synthesis 2 (ACS2) and ACS6 expression, but an advance in MYC2 expression,indicating that NIMIN1,2 are essential for B. cinerea-activated jasmonic acid (JA)/ethylene(ET) biosynthesis and signaling. However, mutation in NIMIN1 or NIMIN2 drastically suppressed JA-, but not ET-activated PDF1.2 expression. Together, these results suggest that NIMIN1,2 may positively control the B. cinerea resistance by mediating redox homeostasis and JA/ET pathways in Arabidopsis.

Wood forming tissue-specific expression of PdSuSy and HCHL increases holocellulose content and improves saccharification in Populus

Development of strategies to deconstruct lignocellulosic biomass in tree species is essential for biofuels and biomaterials production.We applied a wood forming tissue-specific system in a hybrid poplar to express both PdSuSy(a sucrose synthase gene from Populus deltoides×P.euramericana that has not been functionally characterized)and HCHL(the hydroxycinnamoyl-CoA hydratase-lyase gene from Pseudomonas fluorescens,which inhibits lignin polymerization in Arabidopsis).The PdSuSy-HCHL overexpression poplars correspondingly driven by the promoters of Arabidopsis AtCesA7 and AtC4 H resulted in a significant increase in cellulose(>8%),xylan(>12%)and glucose(>29%)content,accompanying a reduction in galacturonic acid(>36%)content,compared to control plants.The saccharification efficiency of these overexpression poplars was dramatically increased by up to 27%,but total lignin content was unaffected.These transgenic poplars showed inhibited growth characteristics,including>16%reduced plant height,>10% reduced number of internodes,and>18% reduced fresh weight after growth of 4 months,possibly due to relatively low expression of HCHL in secondary xylem.Our results demonstrate the structural complexity and interaction of the cell wall polymers in wood tissue and outline a potential method to increase biomass saccharification in woody species.

Fine-tuning brassinosteroid biosynthesis via 3′UTR-dependent decay of CPD mRNA modulates wood formation in Populus

Brassinosteroids(BRs)are plant hormones that regulate wood formation in trees.Currently,little is known about the post-transcriptional regulation of BR synthesis.Here,we show that during wood formation,fine-tuning BR synthesis requires 3′UTR-dependent decay of Populus CONSTITUTIVE PHOTOMORPHOGENIC DWARF 1(PdCPD1).Overexpression of PdCPD1 or its 3′UTR fragment resulted in a significant increase of BR levels and inhibited secondary growth.In contrast,transgenic poplars repressing PdCPD13′UTR expression displayed moderate levels of BR and promoted wood formation.We show that the Populus GLYCINE-RICH RNA-BINDING PROTEIN1(PdGRP1)directly binds to a GU-rich element in 3′UTR of Pd CPD1,leading to its mRNA decay.We thus provide a post-transcriptional mechanism underlying BRs synthesis during wood formation,which may be useful for genetic manipulation of wood biomass in trees.