Molecular Basis Of Cold-Induced Pollen Sterility In Rice.

Cold-induced pollen sterility is the most yield-affecting problem for the Australian rice industry,leading to yield losses of 20-40%,or A$15-29 million, on average every 3-4 years. The molecular basis of the problem remains largely unknown, and breeding efforts have been largely unsuccessful due to the lack of reliable selection techniques in the field/glass house, and the lack of molecular markers for selection of coldtolerant lines. Identification of the molecular basis of the problem may lead to the identification of markers that will greatly facilitate breeding of cold-tolerant Australian rice varieties. Our starting point was to study the accumulation of sucrose that occurs in anthers after cold treatment. We investigated whether cold affects expression of a gene involved in sucrose metabolism, thereby introducing a metabolic block in sucrose metabolism

Molecular Basis Of Cold-Induced Pollen Sterility In Rice

We have used two approaches to study the molecular basis of cold-induced pollen sterility in rice. Firstly, we studied the effect of cold on sugar metabolism in rice anthers, with the intention to identify genes that are affected by cold. Secondly, we used microarray gene expression profiling to identify rice genes that are affected by cold treatment, and to compare the cold response between a cold-tolerant and a coldsensitive variety. The work on sugar metabolism has shown that cold treatment of rice anthers leads to an absence of starch accumulation and non-viability of pollen. Starch is an essential source of energy for pollen development and pollen fertility. At the same time, we found that sucrose – the building block of starch – is accumulating in cold-stressed anthers at the cold-sensitive young microspore stage. This indicates that sucrose somehow fails to be converted to starch in the pollen grains, and that the supply mechanism of sugar to the tapetum and developing pollen grains is disturbed by cold. The tapetum, the cell layer in the anther that feeds the pollen grains, and the pollen cells are physically isolated from the rest of the anther at the young microspore stage. Supply of sugars from the rest of the anther to the tapetum and pollen grains occurs via a specialised mechanism involving two enzymes: cell wall invertase and monosaccharide transporters. Biochemical analysis indicated that the activity of anther cell wall invertase was significantly repressed by cold, suggesting that the first step in the sugar transport chain is functioning at reduced capacity. We cloned the gene that encodes this enzyme, OSINV4, and found that the expression of this gene is repressed by cold. We subsequently identified two monosaccharide transporter genes: OSMST8 was repressed by cold, while OSMST7 was induced by cold. OSINV4 and OSMST8 function in the same pathway that supplies sucrose to the tapetum and pollen, while OSMST7 functions in a different pathway that may lead to starch accumulation in the anther wall. Studying the cold-tolerant Chinese cultivar R31 revealed that this cultivar did not accumulate sucrose, contained starch-filled fertile pollen grains, and did not repress OSINV4 and OSMST8 expression following cold treatment. Thus, there is a strong correlation between these phenotypes and the cold tolerance phenotype, suggesting that we have now some expression markers for coldtolerance. We have also found that these genes are regulated by the plant hormone ABA; ABA perfectly mimics the effect of cold and it serves as a signal to switch of gene expression, including OSINV4 and OSMST8. ABA-accumulation does not occur to the same extent in R31 than in Doongara, and we have identified an anther ABA biosynthetic gene that is induced by cold (OSNCED3). These findings have improved our understanding of the molecular basis of cold-induced pollen sterility significantly, and we are now in the stage of identifying a marker gene that can be used to follow the cold-tolerance trait in a breeding population. We have also made good progress using the microarray approach. By comparing the cold response of Doongara and two tolerant cultivars (R31 and R32) we identified a non-redundant set of 329 genes that are expressed differently between the different cultivars. The genes were sequenced and their chromosome location was determined. This gave us more information about other cellular processes that are affected by cold and how these processes are affected differently in tolerant and sensitive cultivars. We are now in the stage of spotting these genes on a smaller diagnostic microarray, and this array will be used to screen doubled haploid lines of a Doongara/R31 cross (prepared by Dr. X. Zhao, Sydney Univ.). This will enable us to identify suitable marker genes for cold tolerance in rice

The Trials and Tribulations of the Plant Male Gametophyte — Understanding Reproductive Stage Stress Tolerance

Yield and productivity of many crop species depend on successful reproductive development to produce seeds or fruits for human nutrition. Plants determine the right time to flower based on environmental cues (day length, temperature) and angiosperms have evolved a plethora of mechanisms to adapt flowering to specific environmental conditions. Despite these adaptation mechanisms, fertilisation and seed production remain subject to the reigning weather conditions before and during flowering. To fertilise the immobile female gametes inside the ovule, the male gametophytes need to be dispersed in a hostile environment. In crop plants, unexpected inclement weather conditions during male gametophyte development and pollen dispersal are often associated with dramatic yield losses. Molecular and physiological studies are gradually making progress in identifying genes and processes that control various aspects of pollen development, but the many intricacies involved in environmental control of pollen development and – in particular – regulation of male fertility remain poorly understood. The aim of this paper is to draw attention to the enormous amount of complexity and biodiversity that exist in angiosperm male gametophyte development. A better understanding of the strategies that exist in adapting pollen production and fertility to environmental challenges may ultimately benefit improvement of abiotic stress tolerance in major food crops

Pollen Developmental Arrest: Maintaining Pollen Fertility in a World With a Changing Climate

During evolution of land plants, the haploid gametophytic stage has been strongly reduced in size and the diploid sporophytic phase has become the dominant growth form. Both male and female gametophytes are parasitic to the sporophyte and reside in separate parts of the flower located either on the same plant or on different plants. For fertilization to occur, bi-cellular or tri-cellular male gametophytes (pollen grains) have to travel to the immobile female gametophyte in the ovary. To survive exposure to a hostile atmosphere, pollen grains are thought to enter a state of complete or partial developmental arrest (DA). DA in pollen is strongly associated with acquisition of desiccation tolerance (DT) to extend pollen viability during air travel, but occurrence of DA in pollen is both species-dependent and at the same time strongly dependent on the reigning environmental conditions at the time of dispersal. Several environmental stresses (heat, drought, cold, humidity) are known to affect pollen production and viability. Climate change is also posing a serious threat to plant reproductive behavior and crop productivity. It is therefore timely to gain a better understanding of how DA and pollen viability are controlled in plants and how pollen viability can be protected to secure crop yields in a changing environment. Here, we provide an overview of how DA and pollen viability are controlled and how the environment affects them. We make emphasis on what is known and areas where a deeper understanding is needed

Genetic improvement of wheat for dry environments - a trait based approach

Item does not contain fulltext23 januari 201

SeagrassDB: An open-source transcriptomics landscape for phylogenetically profiled seagrasses and aquatic plants

© 2018, The Author(s). Seagrasses and aquatic plants are important clades of higher plants, significant for carbon sequestration and marine ecological restoration. They are valuable in the sense that they allow us to understand how plants have developed traits to adapt to high salinity and photosynthetically challenged environments. Here, we present a large-scale phylogenetically profiled transcriptomics repository covering seagrasses and aquatic plants. SeagrassDB encompasses a total of 1,052,262 unigenes with a minimum and maximum contig length of 8,831 bp and 16,705 bp respectively. SeagrassDB provides access to 34,455 transcription factors, 470,568 PFAM domains, 382,528 prosite models and 482,121 InterPro domains across 9 species. SeagrassDB allows for the comparative gene mining using BLAST-based approaches and subsequent unigenes sequence retrieval with associated features such as expression (FPKM values), gene ontologies, functional assignments, family level classification, Interpro domains, KEGG orthology (KO), transcription factors and prosite information. SeagrassDB is available to the scientific community for exploring the functional genic landscape of seagrass and aquatic plants at: http://115.146.91.129/index.php

Determining the Genetic Architecture of Reproductive Stage Drought Tolerance in Wheat Using a Correlated Trait and Correlated Marker Effect Model

Water stress during reproductive growth is a major yield constraint for wheat (Triticum aestivum L). We previously established a controlled environment drought tolerance phenotyping method targeting the young microspore stage of pollen development. This method eliminates stress avoidance based on flowering time. We substituted soil drought treatments by a reproducible osmotic stress treatment using hydroponics and NaCl as osmolyte. Salt exclusion in hexaploid wheat avoids salt toxicity, causing osmotic stress. A Cranbrook x Halberd doubled haploid (DH) population was phenotyped by scoring spike grain numbers of unstressed (SGNCon) and osmotically stressed (SGNTrt) plants. Grain number data were analyzed using a linear mixed model (LMM) that included genetic correlations between the SGNCon and SGNTrt traits. Viewing this as a genetic regression of SGNTrt on SGNCon allowed derivation of a stress tolerance trait (SGNTol). Importantly, and by definition of the trait, the genetic effects for SGNTol are statistically independent of those for SGNCon. Thus they represent non-pleiotropic effects associated with the stress treatment that are independent of the control treatment. QTL mapping was conducted using a whole genome approach in which the LMM included all traits and all markers simultaneously. The marker effects within chromosomes were assumed to follow a spatial correlation model. This resulted in smooth marker profiles that could be used to identify positions of putative QTL. The most influential QTL were located on chromosome 5A for SGNTol (126cM; contributed by Halberd), 5A for SGNCon (141cM; Cranbrook) and 2A for SGNTrt (116cM; Cranbrook). Sensitive and tolerant population tail lines all showed matching soil drought tolerance phenotypes, confirming that osmotic stress is a valid surrogate screening method

The effect of cold stress on the root-specific lipidome of two wheat varieties with contrasting cold tolerance

Complex glycerolipidome analysis of wheat upon low temperature stress has been reported for above-ground tissues only. There are no reports on the effects of cold stress on the root lipidome nor on tissue-specific responses of cold stress wheat roots. This study aims to investigate the changes of lipid profiles in the different developmental zones of the seedling roots of two wheat varieties with contrasting cold tolerance exposed to chilling and freezing temperatures. We analyzed 273 lipid species derived from 21 lipid classes using a targeted profiling approach based on MS/MS data acquired from schedule parallel reaction monitoring assays. For both the tolerant Young and sensitive Wyalkatchem species, cold stress increased the phosphatidylcholine and phosphatidylethanolamine compositions, but decreased the monohexosyl ceramide compositions in the root zones. We show that the difference between the two varieties with contrasting cold tolerance could be attributed to the change in the individual lipid species, rather than the fluctuation of the whole lipid classes. The outcomes gained from this study may advance our understanding of the mechanisms of wheat adaptation to cold and contribute to wheat breeding for the improvement of cold-tolerance