Heat stress often results in the generation of reactive oxygen species, such as hydrogen peroxide, which plays a vital role as a secondary messenger in the process of abscisic acid (ABA)-mediated stomatal closure. Here, we characterized the rice (Oryza sativa) HEAT TOLERANCE AT SEEDLING STAGE (OsHTAS) gene, which plays a positive role in heat tolerance at the seedling stage. OsHTAS encodes a ubiquitin ligase localized to the nucleus and cytoplasm. OsHTAS expression was detected in all tissues surveyed and peaked in leaf blade, in which the expression was concentrated in mesophyll cells. OsHTAS was responsive to multiple stresses and was strongly induced by exogenous ABA. In yeast two-hybrid assays, OsHTAS interacted with components of the ubiquitin/26S proteasome system and an isoform of rice ascorbate peroxidase. OsHTAS modulated hydrogen peroxide accumulation in shoots, altered the stomatal aperture status of rice leaves, and promoted ABA biosynthesis. The results suggested that the RING finger ubiquitin E3 ligase OsHTAS functions in leaf blade to enhance heat tolerance through modulation of hydrogen peroxide-induced stomatal closure and is involved in both ABA-dependent and DROUGHT AND SALT TOLERANCE-mediated pathways.
BackgroundLysine (Lys) is considered to be the first limiting essential amino acid in rice. Although there have been extensive efforts to improve the Lys content of rice through traditional breeding and genetic engineering, no satisfactory products have been achieved to date.ResultsWe expressed a LYSINE-RICH PROTEIN gene (LRP) from Psophocarpus tetragonolobus (L.) DC using an endosperm-specific GLUTELIN1 promoter (GT1) in Peiai64S (PA64S), an elite photoperiod-thermo sensitive male sterility (PTSMS) line. The expression of the foreign LRP protein was confirmed by Western blot analysis. The Lys level in the transgenic rice seeds increased more than 30 %, the total amount of other amino acids also increased compared to wild-type. Persistent investigation of amino acids in 3 generations showed that the Lys content was significantly increased in seeds of transgenic rice. Furthermore, Lys content in the hybrid of the transgenic plants also had an approximate 20 % increase compared to hybrid control. At the grain-filling stage, we monitored the transcript abundance of many genes encoding key enzymes involved in amino acid metabolism, and the results suggested that reduced amino acid catabolism led to the accumulation of amino acids in the transgenic plants. The genetically engineered rice showed unfavorable grain phenotypes compared to wild-type, however, its hybrid displayed little negative effects on grain.ConclusionsEndosperm-specific expression of foreign LRP significantly increased the Lys content in the seeds of transgenic plant, and the the Lys increase was stably heritable with 3 generation investigation. The hybrid of the transgenic plants also showed significant increases of Lys content in the seeds. These results indicated that expression of LRP in rice seeds may have promising applications in improving Lys levels in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0837-x) contains supplementary material, which is available to authorized users.
Flavonoids are involved in many physiological processes in plants. TRANSPARENT TESTA 4 (TT4) acts at the first step of flavonoid biosynthesis, and the loss of TT4 function causes a lack of flavonoid. Flavonoid deficiency is reportedly the main cause of increased fatty acid content in pale-coloured oilseeds, but details regarding the relationship between seed flavonoids and fatty acid biosynthesis are elusive. In this work, we applied a genetic strategy combined with biochemical and cytological assays to determine the effect of seed flavonoids on the biosynthesis of fatty acids in Arabidopsis thaliana. We showed that TT4-mediated flavonoids negatively affect embryonic fatty acid biosynthesis. A crossing experiment indicated that seed flavonoid biosynthesis and the impact of this process on fatty acid biosynthesis were controlled in a maternal line-dependent manner. Loss of TT4 function activated glycolysis in seed embryos, thereby enhancing fatty acid biosynthesis, but did not improve seed mucilage production. Moreover, loss of TT4 function reduced PIN-FORMED 4 expression and subsequently increased auxin accumulation in embryos. Pharmacologically and genetically elevated auxin levels enhanced seed fatty acid biosynthesis. These results indicated that flavonoids affect fatty acid biosynthesis by carbon source reallocation via regulation of WRINKLE1 and auxin transport.
Gene pyramiding is an efficient approach for the genetic improvement of multiple agronomic traits simultaneously. In this study, we pyramided two foreign genes, cry1Ac driven by the rice Actin I promoter, and lysine-rich protein (LRP), driven by the endosperm-specific GLUTELIN1 (GT1) promoter, into the elite indica cultivar 9311. These two genes were chosen in an attempt to enhance insect-resistance and Lysine (Lys) content. In the pyramided line, the foreign gene cry1Ac was efficiently expressed in the leaves and stems, and exhibited highly efficient resistance to striped stem borer (SSB, Chilo suppressalis Walker) in the laboratory and rice leaf folder (RLF, Cnaphalocrocis medinalis Guenee) in the field. Furthermore, the LRP gene was highly expressed in the endosperm and produced a remarkable increase of Lys content in the seeds of the pyramided line. The data from field trials demonstrated that most of the agronomic traits including yield were well maintained in the pyramided line compared to the parental control. These results strongly suggest that the foreign cry1Ac and LRP genes have remarkable application potential in rice, and the resultant pyramided line serves as an ideal bridge material for the improvement of insect-resistance and high Lys rice in the future.
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