Maize seed storage proteins are a major source of human and livestock consumption. However, these proteins have poor nutritional value, because they are deficient in lysine and tryptophan. Much research has been done to elevate the lysine content by reducing zein content or regulating the activities of key enzymes in lysine metabolism. Using the naturally lysine-rich protein genes, sb401 and SBgLR, from potato, we previously increased the lysine and protein contents of maize seeds. Here, we examined another natural lysine-rich protein gene, GhLRP, from cotton, which increased the lysine content of transgenic maize seeds at levels varying from 16.2% to 65.0% relative to the wild-type. The total protein content was not distinctly different, except in the six transgenic lines. The lipid and starch levels did not differ substantially in Gossypium hirsutum L. lysine-rich protein (GhLRP) transgenic kernels when compared to wild-type. The agronomic characteristics of all the transgenic maize were also normal. GhLRP is a high-lysine protein candidate gene for increasing the lysine content of maize. This study provided a valuable model system for improving maize lysine content.

Remorin genes encode plant-specific and plasma-membrane-associated proteins that play important roles in several plant physiological processes and adaptations to environmental adaptations. However, little is known regarding the remorin gene family in foxtail millet (Setaria italica), a traditional drought-resistant crop that grows in China. In this study, 21 remorin genes in the foxtail millet genome were identified, renamed according to their chromosomal distribution, and classified into four main groups based on their phylogenetic relationships and structural features. Additionally, we found that SiREM gene family expansion was primarily because of whole- genome duplication and segmental duplication events. Evolutionary changes in the remorin family in Poaceae crops were clarified via synteny analyses. Gene expression analyses through RT-PCR and qRT-PCR indicated that SiREM genes influenced millet growth and development, particularly SiREM1, 4, 11, and 12. Concurrently, SiREM genes expression showed inconsistent response to phytohormone treatments and abiotic stresses, suggesting that they are regulated by different signaling pathways. This systematic reanalysis remorin gene family in the foxtail millet provides fundamental information about the biological functions associated with growth, development, and stress tolerance and evolutionary characteristics, thus helping in elucidating the molecular mechanism and improving the agricultural traits of this crop in the future.

Maize (Zea mays) seed is deficient in protein and lysine content. Many studies have been made to improve the nutritional quality of maize seeds. Previously, we reported the role of a natural lysine-rich protein gene SBgLR in increasing protein and lysine content. However, how the SBgLR improves lysine and protein content remains unclear. Here, the reasons and possible mechanism for SBgLR in protein and lysine improvement have been analyzed and discussed. Through seed-specific expression of SBgLR, we obtained transgenic maize with the simultaneously increased lysine and protein contents. High-protein and high-lysine characters were stably inherited across generations. The expression of SBgLR in maize kernels increased the accumulation of both zeins and non-zein proteins. Transmission electron microscopy showed that the number of protein bodies (PBs) was increased obviously in SBgLR transgenic immature endosperms with the morphology and structure of PBs unchanged. The proteinaceous matrix was more abundant in transgenic mature endosperms under scanning electron microscopy. The stabilities of zein and lysine-rich non-zein genes were also increased in transgenic endosperms. Finally, the potential application of SBgLR in maize nutrient improvement was evaluated. This study shows that a cytoskeleton-associated protein has potential applicable value in crop nutrient improving, and provided a feasible strategy for improvement of maize grain quality.