Root branching under high salinity requires auxin-independent modulation of LATERAL ORGAN BOUNDARY DOMAIN 16 function.

Salinity stress constrains lateral root (LR) growth and severely affects plant growth. Auxin signaling regulates LR formation, but the molecular mechanism by which salinity affects root auxin signaling and whether salt induces other pathways that regulate LR development remains unknown. In Arabidopsis thaliana, the auxin-regulated transcription factor LATERAL ORGAN BOUNDARY DOMAIN 16 (LBD16) is an essential player in LR development under control conditions. Here, we show that under high-salt conditions, an alternative pathway regulates LBD16 expression. Salt represses auxin signaling but, in parallel, activates ZINC FINGER OF ARABIDOPSIS THALIANA 6 (ZAT6), a transcriptional activator of LBD16. ZAT6 activates LBD16 expression, thus contributing to downstream cell wall remodeling and promoting LR development under high-salt conditions. Our study thus shows that the integration of auxin-dependent repressive and salt-activated auxin-independent pathways converging on LBD16 modulates root branching under high-salt conditions.

Overexpression of PbrNHX2 gene, a Na+/H+ antiporter gene isolated from Pyrus betulaefolia, confers enhanced tolerance to salt stress via modulating ROS levels.

Intracellular Na+/H+ antiporters (NHXs) play important roles in plant tolerance to salt stress. However, plant NHXs functioning in salt tolerance and the underlying physiological mechanisms remain poorly understood. In this report, we report the identification and functional characterization of PbrNHX2 isolated from Pyrus betulaefolia. PbrNHX2 expression levels were induced by salt, and dehydration, but was unaffected by cold. PbrNHX2 was localized in the tonoplast. Overexpression of PbrNHX2 in tobacco and Pyrus ussuriensis conferred enhanced tolerance to salt tolerance, whereas down-regulation of PbrNHX2 in Pyrus betulaefolia by virus-induced gene silencing (VIGS) resulted in elevated salt sensitivity. The transgenic lines contained lower levels of Na+, higher levels of K+, and higher K/Na ratio, whereas they were changed in an opposite way when PbrNHX2 was silenced. In addition, the transgenic plants accumulated lower levels of reactive oxygen species compared with wild type, accompanied by higher activities of three antioxidant enzymes. Taken together, the data demonstrate that PbrNHX2 plays a positive role in salt tolerance and that it holds a great potential for engineering salt tolerance in crops.

Genome-wide analyses and expression patterns under abiotic stress of NAC transcription factors in white pear (Pyrus bretschneideri).

BACKGROUND: Although the genome of Chinese white pear ('Dangshansuli') has been released, little is known about the functions, evolutionary history and expression patterns of NAC families in this species to date. RESULTS: In this study, we identified a total of 183 NAC transcription factors (TFs) in the pear genome, among which 146 pear NAC (PbNAC) members were mapped onto 16 chromosomes, and 37 PbNAC genes were located on scaffold contigs. No PbNAC genes were mapped to chromosome 2. Based on gene structure, protein motif analysis, and topology of the phylogenetic tree, the pear PbNAC family was classified into 33 groups. By comparing and analyzing the unique NAC subgroups in Rosaceae, we identified 19 NAC subgroups specific to pear. We also found that whole-genome duplication (WGD)/segmental duplication played critical roles in the expansion of the NAC family in pear, such as the 83 PbNAC duplicated gene pairs dated back to the two WGD events. Further, we found that purifying selection was the primary force driving the evolution of PbNAC family genes. Next, we used transcriptomic data to study responses to drought and cold stresses in pear, and we found that genes in groups C2f, C72b, and C100a were related to drought and cold stress response. CONCLUSIONS: Through the phylogenetic, evolutionary, and expression analyses of the NAC gene family in Chinese white pear, we indentified 11 PbNAC TFs associated with abiotic stress in pear.