Measuring Nonfoliar Photosynthesis.

Nonfoliar gas exchange provides a noninvasive way to measure photosynthesis and other gas exchange parameters, enabling the assessment of their potential contribution to yield. Photosynthesis in nonfoliar material has been gaining increasing attention due to its contribution to yield, especially under conditions when leaf photosynthesis is compromised. Here, we provide methods and approaches along with examples of measuring gas exchange in nonfoliar material using a specialized chamber.

The Emerging Role of Non-Coding RNAs (ncRNAs) in Plant Growth, Development, and Stress Response Signaling.

Plant species utilize a variety of regulatory mechanisms to ensure sustainable productivity. Within this intricate framework, numerous non-coding RNAs (ncRNAs) play a crucial regulatory role in plant biology, surpassing the essential functions of RNA molecules as messengers, ribosomal, and transfer RNAs. ncRNAs represent an emerging class of regulators, operating directly in the form of small interfering RNAs (siRNAs), microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs). These ncRNAs exert control at various levels, including transcription, post-transcription, translation, and epigenetic. Furthermore, they interact with each other, contributing to a variety of biological processes and mechanisms associated with stress resilience. This review primarily concentrates on the recent advancements in plant ncRNAs, delineating their functions in growth and development across various organs such as root, leaf, seed/endosperm, and seed nutrient development. Additionally, this review broadens its scope by examining the role of ncRNAs in response to environmental stresses such as drought, salt, flood, heat, and cold in plants. This compilation offers updated information and insights to guide the characterization of the potential functions of ncRNAs in plant growth, development, and stress resilience in future research.

High photosynthesis rate in two wild rice species is driven by leaf anatomy mediating high Rubisco activity and electron transport rate.

The importance of increasing photosynthetic efficiency for sustainable crop yield increases to feed the growing world population is well recognized. The natural genetic variation in leaf photosynthesis in crop plants is largely unexploited for increasing yield potential. The genus Oryza, including cultivated rice and wild relatives, offers tremendous genetic variability to explore photosynthetic differences and underlying biochemical, photochemical, and developmental traits. We quantified leaf photosynthesis and related physiological parameters for six cultivated and three wild rice genotypes, and identified photosynthetically efficient wild rice accessions. Fitting A/Ci curves and biochemical analyses showed that leaf photosynthesis in cultivated rice varieties IR 64 and Nipponbare was limited due to leaf nitrogen content, Rubisco activity, and electron transport rate compared with photosynthetically efficient wild rice accessions Oryza australiensis and Oryza latifolia. The selected wild rice accessions with high leaf photosynthesis per unit area had anatomical features such as larger mesophyll cells with more chloroplasts, fewer mesophyll cells between two adjacent veins, and higher mesophyll cell and chloroplast surface area exposed to intercellular space. Our results show the existence of desirable variations in Rubisco activity, electron transport rate, and leaf anatomical features that could be targeted for increasing the photosynthetic efficiency of cultivated rice varieties.

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice.

Source-sink relationships are key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in source-sink relationships between a cultivated rice, Oryza sativa cv. Nipponbare, and a wild rice, Oryza australiensis, which show striking differences in biomass and grain yield. Oryza australiensis, which accumulates a higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves compared with Nipponbare. However, grain features and sugar content suggested limited sucrose mobilization to grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in O. australiensis stem indicated that it utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, source-sink relationships favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in source-sink relationships between Nipponbare and O. australiensis.

Sucrose transport in response to drought and salt stress involves ABA-mediated induction of OsSWEET13 and OsSWEET15 in rice.

Abiotic stresses, including drought and salinity, negatively affect plant development and physiology at molecular and metabolic levels. Sucrose transport, mediating distribution of photosynthates in plant, is a key physiological process impacted by drought and salinity stresses, as sucrose is a prime energy and signaling molecule as well as an osmolyte. Therefore, understanding the effects of abiotic stresses on sucrose transport and transporters, and underlying genetic and molecular mechanisms, is imperative to maintain sugar homeostasis in plants under stress. Here, we investigated the effects of drought and salinity stresses on sucrose transport and distribution, and on expression levels of genes encoding Sugars Will Eventually be Exported Transporters (SWEETs), along with a potential transcription factor regulating SWEET expression in rice. We observed that drought and salinity stresses increased the sucrose content in leaf and root tissues and in phloem sap of rice indica varieties. Expression analyses of SWEET genes and histochemical analysis of ß-glucuronidase-reporter transgenic plants suggested that OsSWEET13 and OsSWEET15 are major SWEET transporters regulating the sucrose transport and levels in response to the abiotic stresses. Transactivation analyses showed that an abscisic acid (ABA)-responsive transcription factor OsbZIP72 directly binds to the promoters of OsSWEET13 and OsSWEET15 and activates their expression. Taken together, the results showed that the higher expressions of OsSWEET13 and OsSWEET15 genes, induced by binding of an ABA-responsive transcription factor OsbZIP72 to the promoters, potentially modulate sucrose transport and distribution in response to the abiotic stresses. The mechanism could possibly be targeted for maintaining sugar homeostasis in rice under drought and salinity stresses.

Production and cytological characterization of a synthetic amphiploid derived from a cross between Oryza sativa and Oryza punctata.

Oryza punctata Kotschy ex Steud. (BB, 2n = 24) is a wild species of rice that has many useful agronomic traits. An interspecific hybrid (AB, 2n = 24) was produced by crossing O. punctata and Oryza sativa variety Punjab Rice 122 (PR122, AA, 2n = 24) to broaden the narrow genetic base of cultivated rice. Cytological analysis of the pollen mother cells (PMCs) of the interspecific hybrids confirmed that they have 24 chromosomes. The F1 hybrids showed the presence of 19-20 univalents and 1-3 bivalents. The interspecific hybrid was treated with colchicine to produce a synthetic amphiploid (AABB, 2n = 48). Pollen fertility of the synthetic amphiploid was found to be greater than 50% and partial seed set was observed. Chromosome numbers in the PMCs of the synthetic amphiploid were 24II, showing normal pairing. Flow cytometric analysis also confirmed doubled genomic content in the synthetic amphiploid. Leaf morphological and anatomical studies of the synthetic amphiploid showed higher chlorophyll content and enlarged bundle sheath cells as compared with both of its parents. The synthetic amphiploid was backcrossed with PR122 to develop a series of addition and substitution lines for the transfer of useful genes from O. punctata with least linkage drag.

Enhancing crop yield by optimizing plant developmental features.

A number of plant features and traits, such as overall plant architecture, leaf structure and morphological features, vascular architecture and flowering time are important determinants of photosynthetic efficiency and hence the overall performance of crop plants. The optimization of such developmental traits thus has great potential to increase biomass and crop yield. Here, we provide a comprehensive review of these developmental traits in crop plants, summarizing their genetic regulation and highlighting the potential of manipulating these traits for crop improvement. We also briefly review the effects of domestication on the developmental features of crop plants. Finally, we discuss the potential of functional genomics-based approaches to optimize plant developmental traits to increase yield.