Tagiri, A. | Search bioRxiv

bioRxiv2023

Conserved cis-acting motifs and localization of transcripts and proteins of MFT2 in barley and rice

MFT is an important regulator of seed dormancy in flowering plants. A natural mutation in the A-box motif in the promoter of wheat (Triticum aestivum) MFT2 on chromosome 3A (TaMFT2-3A) has been used to prevent pre-harvest sprouting (PHS) in wheat cultivars in East Asia. Previous research using in situ hybridization showed that TaMFT2-3A is primarily expressed in the seed scutellum. In this study, we analyzed the localization of transcripts and encoded proteins for the TaMFT2 homologs from barley (Hordeum vulgare) and rice (Oryza sativa), HvMFT2 and OsMFT2, respectively. RNA in situ hybridization showed that, like the wheat genes, the rice and barley homologs are primarily expressed in the scutellum, indicating that these three MFT2 genes have a common expression pattern during seed development. Analysis of the cis-acting regulatory elements of their promoter sequences showed that the three MFT2 promoters share eight seed-specific cis-acting RY motifs, which are binding sites for B3-domain transcription factors of the AFL-B3 and VIVIPAROUS1/ABI3-LIKE (VAL) families. In addition, we detected tandemly repeated and partially overlapping A-box motifs in the promoters of HvMFT2, TaMFT2-3B, and TaMFT2-3D, possibly explaining why the natural allele of TaMFT2-3A has been employed in breeding. We generated transgenic rice plants expressing nuclear-localized green fluorescent protein (NLS-2xGFP) and OsMFT2-GFP under the control of a 3-kb fragment of the OsMFT2 promoter. Immunohistochemical staining using anti-GFP antibodies mainly detected GFP in the scutellum and scutellar epithelium, which is an important tissue for initiating germination upon seed hydration. We confirmed these results by confocal microscopy of GFP fluorescence in seeds. Our results suggest that MFT2 expression in rice, barley, and wheat might be regulated by a similar network of transcription factors through multi-RY motifs in the MFT2 promoters, with possible roles in scutellar epithelium development.

plant biology↗

bioRxiv2018

Unleashing floret fertility by a mutated homeobox gene improved grain yield during wheat evolution under domestication

Floret fertility is a key trait to determine the number of grains per inflorescence in cereals. During wheat (Triticum sp.) evolution, floret fertility has been increased and current bread wheat (T. aestivum L.) produces three to five grains per spikelet; however, little is known about the genetic basis controlling floret fertility. Here we identify the quantitative trait locus Grain Number Increase 1 (GNI1), encoding a homeodomain leucine zipper class I (HD-Zip I) transcription factor. GNI1 evolved in the Triticeae through gene duplication and functionalization. GNI1 was predominantly expressed in the most apical floret primordia and parts of the rachilla, suggesting that GNI1 inhibits rachilla growth and development. GNI1 expression decreased during wheat evolution, and as a consequence, more fertile florets and grains per spikelet are being produced. Genetic analysis revealed that the reduced-function allele of GNI1-A contributes to increase the number of fertile florets per spikelet. The knockdown of GNI1 in transgenic hexaploid wheat improved fertile floret and grain number. Furthermore, wheat plants carrying the impaired allele increased grain yield under field conditions. Our findings illuminate that gene duplication and functionalization generated evolutionary novelty for floret fertility (i.e. reducing floral numbers) while the mutations towards increased grain production were under selection during wheat evolution under domestication.\n\nSignificance StatementGrain number is a fundamental trait for cereal grain yield; but its underlying genetic basis is mainly unknown in wheat. Here we show for the first time a direct link between increased floret fertility, higher grain number per spike and higher plot-yields of wheat in the field. We have identified GNI1 gene encoding an HD-Zip I transcription factor responsible for increased floret fertility. The wild type allele imposes an inhibitory role specifically during rachilla development, indicating that expression of this protein actively shuts-down grain yield potential; whereas, the reduced-function allele enables more florets and grains to be produced. GNI1 evolved through gene duplication in Triticeae and its mutations were under parallel human selection during wheat and barley evolution under domestication.

plant biology↗