HEAT-INDUCED TAS1 TARGET1Mediates Thermotolerance via HEAT STRESS TRANSCRIPTION FACTOR A1a–Directed Pathways inArabidopsis   

Abstract

Many heat stress transcription factors (Hsfs) and heat shock proteins (Hsps) have been identified to play important roles in the heat tolerance of plants. However, many of the key factors mediating the heat response pathways remain unknown. Here, we report that two genes, which are targets of TAS1 (trans-acting siRNA precursor 1)-derived small interfering RNAs that we named HEAT-INDUCED TAS1 TARGET1 (HTT1) and HTT2, are involved in thermotolerance. Microarray analysis revealed that the HTT1 and HTT2 genes were highly upregulated in Arabidopsis thaliana seedlings in response to heat shock. Overexpression of TAS1a, whose trans-acting small interfering RNAs target the HTT genes, elevated accumulation of TAS1-siRNAs and reduced expression levels of the HTT genes, causing weaker thermotolerance. By contrast, overexpression of HTT1 and HTT2 upregulated several Hsf genes, leading to stronger thermotolerance. In heat-tolerant plants overexpressing HsfA1a, the HTT genes were upregulated, especially at high temperatures. Meanwhile, HsfA1a directly activated HTT1 and HTT2 through binding to their promoters. HTT1 interacted with the heat shock proteins Hsp70-14 and Hsp40 and NUCLEAR FACTOR Y, SUBUNIT C2. Taken together, these results suggest that HTT1 mediates thermotolerance pathways because it is targeted by TAS1a, mainly activated by HsfA1a, and acts as cofactor of Hsp70-14 complexes.

Abiotic stress miRNomes in the Triticeae

“…Overexpression of PPR40 / At3g16890 enhanced salinity tolerance in Arabidopsis (Zsigmond et al 2012). Similarly, TAS1 -ta-siRNA targets, At4g29760 , At4g29770 , and At5g18040 (designated as Heat Induced TAS1 Target genes, HTT4 , HTT1 and HTT2 , respectively), were responsive to heat stress and downregulation of these targets reduced heat tolerance in Arabidopsis (Li et al 2014). Of these targets, At4g29760 and At5g18040 , along with another potential TAS1 -ta-siRNA target, At1g51670 , also showed contrasting expression levels compared to TAS1 originating ta-siRNAs in response to cold stress (Kume et al 2010).…”

Small RNAs in regulating temperature stress response in plants

“…It was also found that HTT1 interacted with the heat shock proteins HSP70‐14 and HSP40 in Arabidopsis . These results suggest that HTT1 mediates thermotolerance pathways targeted by TAS1a , mainly activated by HSFA1a , and acts as cofactor of HSP70‐14 complexes (Li et al ; Figure ).…”

“…Plant genomes also encode a unique class of sRNAs called trans‐acting small interfering RNAs (ta‐siRNAs) which exert their functions through posttranscriptional gene silencing (Li et al ). In Arabidopsis , there are four families of noncoding precursor genes generating ta‐siRNA: trans‐acting siRNA precursor 1 ( TAS1) , TAS2 , TAS3 and TAS4 .…”

“…Moreover, the transcription of HTT genes was upregulated in heat‐tolerant plants overexpressing HSFA1a . It was shown that HSFA1a directly binds to HTT promoters to activate their expression (Li et al ). It was also found that HTT1 interacted with the heat shock proteins HSP70‐14 and HSP40 in Arabidopsis .…”

Epigenetic responses to heat stress at different time scales and the involvement of small RNAs

“…The repression of target genes by miRNAs may be especially suited to integrate stress responses over time, as, in the case of translational inhibition, the repression is reversible and a degradation of the miRNA will quickly relieve the block on translation. Other small RNAs (miR398, TAS1) were recently implicated in the acquisition of thermotolerance, 31,32 however, it remains to be tested whether they also play a role in heat stress memory.…”