Over‐expression of mutated ZmDA1 or ZmDAR1 gene improves maize kernel yield by enhancing starch synthesis

Grain weight and grain number are important crop yield determinants. DA1 and DAR1 are the ubiquitin receptors that function as the negative regulators of cell proliferation during development in Arabidopsis. An arginine to lysine mutant at amino acid site 358 could lead to the da1‐1 phenotype, which results in an increased organ size and larger seeds. In this study, the mutated ZmDA1 (Zmda1) and mutated ZmDAR1 (Zmdar1) driven by the maize ubiquitin promoter were separately introduced into maize elite inbred line DH4866. The grain yield of the transgenic plants was 15% greater than that of the wild‐type in 3 years of field trials due to improvements in the grain number, weight and starch content. Interestingly, the over‐expression of Zmda1 and Zmdar1 promoted kernel development, resulting in a more developed basal endosperm transfer cell layer (BETL) than WT and enhanced expression of starch synthase genes. This study suggests that the over‐expression of the mutated ZmDA1 or ZmDAR1 genes improves the sugar imports into the sink organ and starch synthesis in maize kernels.     

Chromatin interacting factor OsVIL2 increases biomass and rice grain yield

Grain number is an important agronomic trait. We investigated the roles of chromatin interacting factor Oryza sativa VIN3‐LIKE 2 (OsVIL2), which controls plant biomass and yield in rice. Mutations in OsVIL2 led to shorter plants and fewer grains whereas its overexpression (OX) enhanced biomass production and grain numbers when compared with the wild type. RNA‐sequencing analyses revealed that 1958 genes were up‐regulated and 2096 genes were down‐regulated in the region of active division within the first internodes of OX plants. Chromatin immunoprecipitation analysis showed that, among the downregulated genes, OsVIL2 was directly associated with chromatins in the promoter region of CYTOKININ OXIDASE/DEHYDROGENASE2 (OsCKX2), a gene responsible for cytokinin degradation. Likewise, active cytokinin levels were increased in the OX plants. We conclude that OsVIL2 improves the production of biomass and grain by suppressing OsCKX2 chromatin.     

Transgenic alteration of ethylene biosynthesis increases grain yield in maize under field drought‐stress conditions

A transgenic gene‐silencing approach was used to modulate the levels of ethylene biosynthesis in maize (Zea mays L.) and determine its effect on grain yield under drought stress in a comprehensive set of field trials. Commercially relevant transgenic events were created with down‐regulated ACC synthases (ACSs), enzymes that catalyse the rate‐limiting step in ethylene biosynthesis. These events had ethylene emission levels reduced approximately 50% compared with nontransgenic nulls. Multiple, independent transgenic hybrids and controls were tested in field trials at managed drought‐stress and rain‐fed locations throughout the US. Analysis of yield data indicated that transgenic events had significantly increased grain yield over the null comparators, with the best event having a 0.58 Mg/ha (9.3 bushel/acre) increase after a flowering period drought stress. A (genotype × transgene) × environment interaction existed among the events, highlighting the need to better understand the context in which the down‐regulation of ACSs functions in maize. Analysis of secondary traits showed that there was a consistent decrease in the anthesis‐silking interval and a concomitant increase in kernel number/ear in transgene‐positive events versus nulls. Selected events were also field tested under a low‐nitrogen treatment, and the best event was found to have a significant 0.44 Mg/ha (7.1 bushel/acre) yield increase. This set of extensive field evaluations demonstrated that down‐regulating the ethylene biosynthetic pathway can improve the grain yield of maize under abiotic stress conditions.     

PAY1 improves plant architecture and enhances grain yield in rice

Plant architecture, a complex of the important agronomic traits that determine grain yield, is a primary target of artificial selection of rice domestication and improvement. Some important genes affecting plant architecture and grain yield have been isolated and characterized in recent decades; however, their underlying mechanism remains to be elucidated. Here, we report genetic identification and functional analysis of the PLANT ARCHITECTURE AND YIELD 1 (PAY1) gene in rice, which affects plant architecture and grain yield in rice. Transgenic plants over‐expressing PAY1 had twice the number of grains per panicle and consequently produced nearly 38% more grain yield per plant than control plants. Mechanistically, PAY1 could improve plant architecture via affecting polar auxin transport activity and altering endogenous indole‐3‐acetic acid distribution. Furthermore, introgression of PAY1 into elite rice cultivars, using marker‐assisted background selection, dramatically increased grain yield compared with the recipient parents. Overall, these results demonstrated that PAY1 could be a new beneficial genetic resource for shaping ideal plant architecture and breeding high‐yielding rice varieties.     

Altered expression of the PTR/NRT1 homologue OsPTR9 affects nitrogen utilization efficiency,growth and grain yield in rice

The plant PTR/NRT1 (peptide transporter/nitrate transporter 1) gene family comprises di/tripeptide and low‐affinity nitrate transporters; some members also recognize other substrates such as carboxylates, phytohormones (auxin and abscisic acid), or defence compounds (glucosinolates). Little is known about the members of this gene family in rice (Oryza sativa L.). Here, we report the influence of altered OsPTR9 expression on nitrogen utilization efficiency, growth, and grain yield. OsPTR9 expression is regulated by exogenous nitrogen and by the day‐night cycle. Elevated expression of OsPTR9 in transgenic rice plants resulted in enhanced ammonium uptake, promotion of lateral root formation and increased grain yield. On the other hand, down‐regulation of OsPTR9 in a T‐DNA insertion line (osptr9) and in OsPTR9‐RNAi rice plants had the opposite effect. These results suggest that OsPTR9 might hold potential for improving nitrogen utilization efficiency and grain yield in rice breeding.     

Expression of the Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) improves the shoot biomass of transgenic barley and increases grain yield in a saline field

Cereal varieties with improved salinity tolerance are needed to achieve profitable grain yields in saline soils. The expression of AVP1, an Arabidopsis gene encoding a vacuolar proton pumping pyrophosphatase (H⁺‐PPase), has been shown to improve the salinity tolerance of transgenic plants in greenhouse conditions. However, the potential for this gene to improve the grain yield of cereal crops in a saline field has yet to be evaluated. Recent advances in high‐throughput nondestructive phenotyping technologies also offer an opportunity to quantitatively evaluate the growth of transgenic plants under abiotic stress through time. In this study, the growth of transgenic barley expressing AVP1 was evaluated under saline conditions in a pot experiment using nondestructive plant imaging and in a saline field trial. Greenhouse‐grown transgenic barley expressing AVP1 produced a larger shoot biomass compared to null segregants, as determined by an increase in projected shoot area, when grown in soil with 150 mm NaCl. This increase in shoot biomass of transgenic AVP1 barley occurred from an early growth stage and also in nonsaline conditions. In a saline field, the transgenic barley expressing AVP1 also showed an increase in shoot biomass and, importantly, produced a greater grain yield per plant compared to wild‐type plants. Interestingly, the expression of AVP1 did not alter barley leaf sodium concentrations in either greenhouse‐ or field‐grown plants. This study validates our greenhouse‐based experiments and indicates that transgenic barley expressing AVP1 is a promising option for increasing cereal crop productivity in saline fields.     

Effect of carbon dioxide enrichment on chlorophyll content, starch content and starch grain structure in Trifolium subterraneum leaves

Trifolium subterraneum (cv. Dinninup) responds to enriched atmospheric CO₂ in a manner similar to that described by Madsen (1968 and 1976) for tomato. In immature leaves, the total chlorophyll content per unit dry weight and the chlorophyll a:b ratio are significantly lower in plants grown at 0.10 vol% CO₂. Although fully expanded mature leaves partially overcome the deficit in chlorophyll content, the chlorophyll a:b ratio remains substantially lower in these high CO₂ grown plants. The large amount of starch accumulated as irregularly shaped grains appears to disrupt normal chloroplast structure in clover plants grown in enriched atmospheric CO₂. These results indicate the chlorotic appearance of leaves from high CO₂ grown clover plants is due to a decrease in chlorophyll content per dry weight possibly resulting from large starch grains and starch accumulation altering normal chloroplast structure and function.     

弱光胁迫对玉米产量及光合特性的影响

通过在玉米授粉前0～14d、授粉后1～14d、授粉后15～28d3个时期分别进行遮光处理,研究了弱光胁迫对两个玉米品种费玉3号和泰玉2号产量及光合特性的影响.结果表明:各时期弱光胁迫均使玉米产量降低,其中授粉前0～14d弱光处理的产量降幅最大,费玉3号对弱光胁迫的反应较泰玉2号敏感.弱光胁迫后籽粒灌浆高峰出现时间延迟、灌浆速率慢、积累量小;弱光胁迫开始的时间越早,籽粒达到最大灌浆速率的时间(Tmax)越晚.弱光胁迫期内,玉米Chl(a b)、Chla/b、光合速率(Pn)、光系统Ⅱ最大光化学效率(Fv/Fm)和光系统Ⅱ实际光化学效率(ФPSⅡ)显著下降,Chlb相对含量提高,胞间二氧化碳浓度(Ci)和非光化学淬灭系数(NPQ)则显著上升;胁迫结束后,玉米Chl(a b)、Chla/b、Pn、Fv/Fm、ФPSⅡ、Ci和NPQ逐渐恢复接近自然光照条件(CK)水平,而Chlb相对含量下降.表明非气孔因素是弱光胁迫下玉米光合速率降低的原因之一.     

Down‐regulation of OsSPX1 caused semi‐male sterility,resulting in reduction of grain yield in rice

OsSPX1, a rice SPX domain gene, involved in the phosphate (Pi)‐sensing mechanism plays an essential role in the Pi‐signalling network through interaction with OsPHR2. In this study, we focused on the potential function of OsSPX1 during rice reproductive phase. Based on investigation of OsSPX1 antisense and sense transgenic rice lines in the paddy fields, we discovered that the down‐regulation of OsSPX1 caused reduction of seed‐setting rate and filled grain number. Through examination of anthers and pollens of the transgenic and wild‐type plants by microscopy, we found that the antisense of OsSPX1 gene led to semi‐male sterility, with lacking of mature pollen grains and phenotypes with a disordered surface of anthers and pollens. We further conducted rice whole‐genome GeneChip analysis to elucidate the possible molecular mechanism underlying why the down‐regulation of OsSPX1 caused deficiencies in anthers and pollens and lower seed‐setting rate in rice. The down‐regulation of OsSPX1 significantly affected expression of genes involved in carbohydrate metabolism and sugar transport, anther development, cell cycle, etc. These genes may be related to pollen fertility and male gametophyte development. Our study demonstrated that down‐regulation of OsSPX1 disrupted rice normal anther and pollen development by affecting carbohydrate metabolism and sugar transport, leading to semi‐male sterility, and ultimately resulted in low seed‐setting rate and grain yield.     

A sucrose non‐fermenting‐1‐related protein kinase‐1 gene,IbSnRK1, improves starch content,composition, granule size,degree of crystallinity and gelatinization in transgenic sweet potato

Sucrose non‐fermenting‐1‐related protein kinase‐1 (SnRK1) is an essential energy‐sensing regulator and plays a key role in the global control of carbohydrate metabolism. The SnRK1 gene has been found to increase starch accumulation in several plant species. However, its roles in improving starch quality have not been reported to date. In this study, we found that the IbSnRK1 gene was highly expressed in the storage roots of sweet potato and strongly induced by exogenous sucrose. Its expression followed the circandian rhythm. Its overexpression not only increased starch content, but also decreased proportion of amylose, enlarged granule size and improved degree of crystallinity and gelatinization in transgenic sweet potato, which revealed, for the first time, the important roles of SnRK1 in improving starch quality of plants. The genes involved in starch biosynthesis pathway were systematically up‐regulated, and the content of ADP‐glucose as an important precursor for starch biosynthesis and the activities of key enzymes were significantly increased in transgenic sweet potato. These findings indicate that IbSnRK1 improves starch content and quality through systematical up‐regulation of the genes and the increase in key enzyme activities involved in starch biosynthesis pathway in transgenic sweet potato. This gene has the potential to improve starch content and quality in sweet potato and other plants.     

Heterologous expression of the apple hexose transporter MdHT2.2 altered sugar concentration with increasing cell wall invertase activity in tomato fruit

Sugar transporters are necessary to transfer hexose from cell wall spaces into parenchyma cells to boost hexose accumulation to high concentrations in fruit. Here, we have identified an apple hexose transporter (HTs), MdHT2.2, located in the plasma membrane, which is highly expressed in mature fruit. In a yeast system, the MdHT2.2 protein exhibited high ¹⁴C‐fructose and ¹⁴C‐glucose transport activity. In transgenic tomato heterologously expressing MdHT2.2, the levels of both fructose and glucose increased significantly in mature fruit, with sugar being unloaded via the apoplastic pathway, but the level of sucrose decreased significantly. Analysis of enzyme activity and the expression of genes related to sugar metabolism and transport revealed greatly up‐regulated expression of SlLIN5, a key gene encoding cell wall invertase (CWINV), as well as increased CWINV activity in tomatoes transformed with MdHT2.2. Moreover, the levels of fructose, glucose and sucrose recovered nearly to those of the wild type in the sllin5‐edited mutant of the MdHT2.2‐expressing lines. However, the overexpression of MdHT2.2 decreased hexose levels and increased sucrose levels in mature leaves and young fruit, suggesting that the response pathway for the apoplastic hexose signal differs among tomato tissues. The present study identifies a new HTs in apple that is able to take up fructose and glucose into cells and confirms that the apoplastic hexose levels regulated by HT controls CWINV activity to alter carbohydrate partitioning and sugar content.     

The relationship of starch metabolism to grain size in wheat

The present investigation was aimed at determining the levels of important enzymes of starch metabolism at different stages of grain development in wheats differing in final grain size and starch content per grain, to ascertain whether these enzymes have some relationship with grain size and/or starch content. Active starch synthesis in these varieties started from 14 days onward and continued till 35 days after anthesis. Invertase was active only during initial stages of grain development. Sucrose-UDP-glucosyltransferase had maximum activity at the 14 and/or 21 day stage and was present throughout the period of grain development. UDP- and ADP-glucose pyrophosphorylases and amylase were most active during the period of active starch synthesis and at the same time tended to parallel grain size and starch content at different stages of grain development.