Hydrangea (Hydrangea macrophylla) is tolerant of acidic soils in which toxicity generally arises from the presence of the soluble aluminum (Al) ion. When hydrangea is cultivated in acidic soil, its resulting blue sepal color is caused by the Al complex formation of anthocyanin. The concentration of vacuolar Al in blue sepal cells can reach levels in excess of approximately 15 mM, suggesting the existence of an Al-transport and/or storage system. However, until now, no Al transporter has been identified in Al hyperaccumulating plants, animals or microorganisms. To identify the transporter being responsible for Al hyperaccumulation, we prepared a cDNA library from blue sepals according to the sepal maturation stage, and then selected candidate genes using a microarray analysis and an in silico study. Here, we identified the vacuolar and plasma membrane-localized Al transporters genes vacuolar Al transporter (VALT) and plasma membrane Al transporter 1 (PALT1), respectively, which are both members of the aquaporin family. The localization of each protein was confirmed by the transient co-expression of the genes. Reverse transcription-PCR and immunoblotting results indicated that VALT and PALT1 are highly expressed in sepal tissue. The overexpression of VALT and PALT1 in Arabidopsis thaliana conferred Al-tolerance and Al-sensitivity, respectively.

Seeds of soybean (Glycine max L.) are a major source of plant-derived oils. In the past, improvements have been made in the quantity and quality of seed oil. Triacylglycerols (TAGs) are the principal components of soybean seed oil, and understanding the metabolic regulation of TAGs in soybean seeds is essential. Here, we identified four soybean genes encoding TAG lipases, designated as SUGAR DEPENDENT1-1 (GmSDP1-1), GmSDP1-2, GmSDP1-3 and GmSDP1-4; these are homologous to Arabidopsis thaliana SDP1 (AtSDP1). To characterize the function of these genes during grain filling, transgenic lines of soybean were generated via RNA interference to knockdown the expression of all four GmSDP1 genes. The seed oil content of the transgenic soybean lines was significantly increased compared with the wild type (WT). Additionally, fatty acid profiles of the WT and transgenic soybean lines were altered; the content of linoleic acid, a major fatty acid in soybean seeds, was significantly reduced, whereas that of oleic acid was increased in transgenic soybean seeds compared with the WT. Substrate specificity experiments showed that TAG lipase preferentially cleaved oleic acid than linoleic acid in the oil body membrane in WT soybean. This study demonstrates that the GmSDP1 proteins regulate both the TAG content and fatty acid composition of soybean seeds during grain filling. These results provide a novel strategy for improving both the quantity and quality of soybean seed oil.

Summary: Regulation of oil biosynthesis in plant seeds has been extensively studied, and biotechnological approaches have been designed to increase seed oil content. Oil and protein synthesis is negatively correlated in seeds, but the mechanisms controlling interactions between these two pathways are unknown. Here, we identify the molecular mechanism controlling oil and protein content in seeds. We utilized transgenic Arabidopsis thaliana plants overexpressing WRINKLED1 (WRI1), a master transcription factor regulating seed oil biosynthesis, and knockout mutants of major seed storage proteins. Oil and protein biosynthesis in wild‐type plants was sequentially activated during early and late seed development, respectively. The negative correlation between oil and protein contents in seeds arises from competition between the pathways. Extension of WRI1 expression during mid‐phase of seed development significantly enhanced seed oil content. This study demonstrates that temporal activation of genes involved in oil or storage protein biosynthesis determines the oil/protein ratio in Arabidopsis seeds. These results provide novel insights into potential breeding strategies to generate crops with high oil contents in seeds.

Plants accumulate large amounts of storage products in seeds to provide an energy reserve and to supply nutrients for germination and post-germinative growth. Arabidopsis thaliana belongs to the Brassica family, and oil is the main storage product in Arabidopsis seeds. To elucidate the regulatory mechanisms of oil biosynthesis in seeds, we screened for high density seeds (heavy seed) that have a low oil content. HS3 (heavy seed 3) encodes the DEAD-box RNA helicase 22 that is localized to plastids. The triacylglycerol (TAG) content of hs3-1 seeds was 10% lower than that of wild-type (WT) seeds, while the protein content was unchanged. The hs3-1 plants displayed a pale-green phenotype in developing seeds and seedlings, but not in adult leaves. The HS3 expression level was high in developing seeds and seedlings, but was low in stems, rosette leaves and flowers. The plastid gene expression profile of WT developing seeds and seedlings differed from that of hs3-1 developing seeds and seedlings. The expression of several genes was reduced in developing hs3-1 seeds, including accD, a gene that encodes the β subunit of carboxyltransferase, which is one component of acetyl-CoA carboxylase in plastids. In contrast, no differences were observed between the expression profiles of WT and hs3-1 rosette leaves. These results show that HS3 is essential for proper mRNA accumulation of plastid genes during seed development and seedling growth, and suggest that HS3 ensures seed oil biosynthesis by maintaining plastid mRNA levels.