Control of OsARF3a by OsKANADI1 contributes to lemma development in rice

Abstract

SUMMARY In rice (Oryza sativa), the lemma and palea protect the internal organs of the floret，provide nutrients for seed development, and determine grain size. We previously revealed that a trans‐acting small interfering RNA targeting AUXIN RESPONSE FACTORS (tasiR‐ARF) regulates lemma polarity establishment via post‐transcriptional repression of AUXIN RESPONSE FACTORS (ARFs) in rice. TasiR‐ARF formation requires RNA‐DEPENDENT RNA POLYMERASE 6 (RDR6). However, the underlying molecular mechanism of the tasiR‐ARF–ARF regulon in lemma development remains unclear. Here, by genetic screening for suppressors of the thermosensitive mutant osrdr6‐1, we identified three suppressors, huifu 1 (hf1), hf9, and hf17. Mapping‐by‐sequencing revealed that HF1 encodes a MYB transcription factor belonging to the KANADI1 family. The hf1 mutation partially rescued the osrdr6‐1 lemma defect but not the defect in tasiR‐ARF levels. DNA affinity purification sequencing analysis identified 17 725 OsKANADI1‐associated sites, most of which contain the SPBP‐box binding motif (RGAATAWW) and are located in the promoter, protein‐coding, intron, and intergenic regions. Moreover, we found that OsKANADI1 could directly bind to the intron of OsARF3a in vitro and in vivo and promote OsARF3a expression at the transcriptional level. In addition, hf9 and hf17 are intragenic suppressors containing mutations in OsRDR6 that partially rescue tasiR‐ARF levels by restoring OsRDR6 protein levels. Collectively, our results demonstrate that OsKANADI1 and tasiR‐ARFs synergistically maintain the proper expression of OsARF3a and thus contribute to rice lemma development.

The OsSGS3-tasiRNA-OsARF3 module orchestrates abiotic-biotic stress response trade-off in rice

“…3a ), supporting its role in tasiRNA production in rice. As tasiR-ARFs have been shown to regulate rice development 43 , 44 , we next used small RNA gel blots to confirm the accumulation of tasiR-ARFs. Consistently, tasiR-ARFs signals were significantly reduced in ossgs3a-1 mutants but restored in complementation lines (Fig.…”

“…Uncropped versions of all gels or blots are shown in the Source Data files. qRT-PCR analysis of tasiR-ARF was conducted as previously described 43 . OsU6 served as an internal control to normalize the expression of tasiR-ARF.…”

Roles of auxin response factors in rice development and stress responses

“…As a tRNA His guanylyltransferase, AET1 (adaptation to environmental temperature 1) can directly bind to and regulate translational efficiency of mRNA of OsARF19 and OsARF23, so as to participate in auxin signalling responding to high temperature (Chen et al, 2019) (Figure 2b). OsARF3a/2 transcript level is significantly decreased at high temperature conditions, suggesting that OsARF3a/2 plays an important role in temperature responses in rice (Si et al, 2022) (Figure 2b).…”

“…Furthermore, OsMADS29 and OsMADS22 , two key flower organ regulators, are significantly induced by high auxin performance which may explain the abnormal small flowers and enlarged plant architecture observed in osarf19 mutant (Zhang et al, 2016). As a MYB‐like transcription factor, OsKANADI1 can bind and positively regulate the transcriptional level of OsARF3a / OsARF2 (LOC_Os01g48060), which is required for establishing the abaxial–adaxial polarity of lemma in rice (Si et al, 2022). Besides, OsARF3a/2 is negatively regulated by tasiR‐ARFs at post‐transcriptional level to contribute to rice lemma development (Si et al, 2022).…”

“…As a MYB‐like transcription factor, OsKANADI1 can bind and positively regulate the transcriptional level of OsARF3a / OsARF2 (LOC_Os01g48060), which is required for establishing the abaxial–adaxial polarity of lemma in rice (Si et al, 2022). Besides, OsARF3a/2 is negatively regulated by tasiR‐ARFs at post‐transcriptional level to contribute to rice lemma development (Si et al, 2022). In addition, OsETTIN2/OsARF2 promotes awn development in rice (Toriba & Hirano, 2014).…”