High-salinity, drought, and low temperature are three common environmental stress factors that seriously influence plant growth and development worldwide. Recently, microRNAs (miRNAs) have emerged as a class of gene expression regulators that have also been linked to stress responses. However, the relationship between miRNA expression and stress responses is just beginning to be explored. Here, we identified 14 stress-inducible miRNAs using microarray data in which the effects of three abiotic stresses were surveyed in Arabidopsis thaliana. Among them, 10 high-salinity-, four drought-, and 10 cold-regulated miRNAs were detected, respectively. miR168, miR171, and miR396 responded to all of the stresses. Expression profiling by RT-PCR analysis showed great cross-talk among the high-salinity, drought, and cold stress signaling pathways. The existence of stress-related elements in miRNA promoter regions provided further evidence supporting our results. These findings extend the current view about miRNA as ubiquitous regulators under stress conditions.

Background: Genes in the CCCH family encode zinc finger proteins containing the motif with three cysteines and one histidine residues. They have been known to play important roles in RNA processing as RNA-binding proteins in animals. To date, few plant CCCH proteins have been studied functionally.

MicroRNAs (miRNAs) have emerged as a class of regulators of gene expression through posttranscriptional degradation or translational repression in living cells. Increasing evidence points to the important relationship between miRNAs and environmental stress responses, but the regulatory mechanisms in plants are poorly understood. Here, we found that Arabidopsis thaliana intronic miR400 was cotranscribed with its host gene (At1g32583) and downregulated by heat treatment. Intriguingly, an alternative splicing (AS) event that occurred in the intron (306 bp) where MIR400 was located was specifically induced by heat stress. A 100 bp fragment was excised, and the remaining 206 bp intron containing MIR400 transcripts was retained in the host gene. The stress-induced AS event thus resulted in greater accumulation of miR400 primary transcripts and a low level of mature miR400. Together, these results provide the direct evidence that AS acts as a regulatory mechanism linking miRNAs and environmental stress in plants.

Summary Zinc finger proteins are a superfamily involved in many aspects of plant growth and development. However, CCCH‐type zinc finger proteins involved in plant stress tolerance are poorly understood. A cDNA clone designated Gossypium hirsutum zinc finger protein 1 (GhZFP1), which encodes a novel CCCH‐type zinc finger protein, was isolated from a salt‐induced cotton (G. hirsutum) cDNA library using differential hybridization screening and further studied in transgenic tobacco Nicotiana tabacum cv. NC89. Using yeast two‐hybrid screening (Y2H), proteins GZIRD21A (GhZFP1 interacting and responsive to dehydration protein 21A) and GZIPR5 (GhZFP1 interacting and pathogenesis‐related protein 5), which interacted with GhZFP1, were isolated. GhZFP1 contains two typical zinc finger motifs (Cx8Cx5Cx3H and Cx5Cx4Cx3H), a putative nuclear export sequence (NES) and a potential nuclear localization signal (NLS). Transient expression analysis using a GhZFP1::GFP fusion gene in onion epidermal cells indicated a nuclear localization for GhZFP1. RNA blot analysis showed that the GhZFP1 transcript was induced by salt (NaCl), drought and salicylic acid (SA). The regions in GhZFP1 that interact with GZIRD21A and GZIPR5 were identified using truncation mutations. Overexpression of GhZFP1 in transgenic tobacco enhanced tolerance to salt stress and resistance to Rhizoctonia solani. Therefore, it appears that GhZFP1 might be involved as an important regulator in plant responses to abiotic and biotic stresses.

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