Cell wall modifications by α-XYLOSIDASE1 are required for control of seed and fruit size in Arabidopsis.

Cell wall modifications are of pivotal importance during plant development. Among cell wall components, xyloglucans are the major hemicellulose polysaccharide in primary cell walls of dicots and non-graminaceous monocots. They can connect the cellulose microfibril surface to affect cell wall mechanical properties. Changes in xyloglucan structure are known to play an important role in regulating cell growth. Therefore, the degradation of xyloglucan is an important modification that alters the cell wall. The α-XYLOSIDASE1 (XYL1) gene encodes the only α-xylosidase acting on xyloglucans in Arabidopsis thaliana. Here, we showed that mutation of XYL1 strongly influences seed size, seed germination, and fruit elongation. We found that the expression of XYL1 is directly regulated in developing seeds and fruit by the MADS-box transcription factor SEEDSTICK. We demonstrated that XYL1 complements the stk smaller seed phenotype. Finally, by atomic force microscopy, we investigated the role of XYL1 activity in maintaining cell stiffness and growth, confirming the importance of cell wall modulation in shaping organs.

CRISPR-mediated accelerated domestication of African rice landraces.

African Oryza glaberrima and Oryza sativa landraces are considered valuable resources for breeding traits due to their adaptation to local environmental and soil conditions. They often possess superior resistance to endemic pests and tolerance to drought and nutrient deficiencies when compared to the "imported" high production Asian rice varieties. In contrast, "domestication traits" such as seed shattering, lodging, and seed yield are not well established in these African landraces. Therefore, the use of these African varieties for high production agriculture is limited by unpredictable yield and grain quality. We are addressing this shortcoming by developing protocols for genetically transforming African landraces to allow the use of CRISPR-Cas mediated breeding approaches. Here we use as proof of concept the cultivated African landrace Kabre to target selected known "domestication loci" and improve the agronomic potential of Kabre rice. Stable genetic transformation with CRISPR-Cas9-based vectors generated single and simultaneous multiple gene knockouts. Plants with reduced stature to diminish lodging were generated by disrupting the HTD1 gene. Furthermore, three loci shown to control seed size and/or yield (GS3, GW2 and GN1A) were targeted using a multiplex CRISPR-Cas9 construct. This resulted in mutants with significantly improved seed yield. Our study provides an example of how new breeding technologies can accelerate the development of highly productive African landrace rice varieties, an important advancement considering that Africa is a hotspot for worldwide population growth and therefore prone to food shortage.

Carbohydrate reserves and seed development: an overview.

Seeds are one of the most important food sources, providing humans and animals with essential nutrients. These nutrients include carbohydrates, lipids, proteins, vitamins and minerals. Carbohydrates are one of the main energy sources for both plant and animal cells and play a fundamental role in seed development, human nutrition and the food industry. Many studies have focused on the molecular pathways that control carbohydrate flow during seed development in monocot and dicot species. For this reason, an overview of seed biodiversity focused on the multiple metabolic and physiological mechanisms that govern seed carbohydrate storage function in the plant kingdom is required. A large number of mutants affecting carbohydrate metabolism, which display defective seed development, are currently available for many plant species. The physiological, biochemical and biomolecular study of such mutants has led researchers to understand better how metabolism of carbohydrates works in plants and the critical role that these carbohydrates, and especially starch, play during seed development. In this review, we summarize and analyze the newest findings related to carbohydrate metabolism's effects on seed development, pointing out key regulatory genes and enzymes that influence seed sugar import and metabolism. Our review also aims to provide guidelines for future research in the field and in this way to assist seed quality optimization by targeted genetic engineering and classical breeding programs.

A Genomic View of Alternative Splicing of Long Non-coding RNAs during Rice Seed Development Reveals Extensive Splicing and lncRNA Gene Families.

Alternative splicing (AS) is a key modulator of development in many eukaryotic organisms. In plants, alternative splice forms of non-coding RNAs (ncRNAs) are known to modulate flowering time in Arabidopsis and fertility in rice. Here we demonstrate that alternative splicing of coding and long non-coding RNAs occurs during rice seed development by comparing AS in immature seeds vs. embryo and endosperm of mature seeds. Based on computational predictions of AS events determined from a Bayesian analysis of junction counts of RNA-seq datasets, differential splicing of protein-coding, and non-coding RNAs was determined. In contrast to roots, leaves, flowers, buds, and reproductive meristems, developing seeds had 5.8-57 times more predicted AS. Primers designed to span introns and exons were used to detect AS events predicted by rMATs in cDNA derived from early (milk) seed, embryo, and endosperm. Comparing milk seed vs. mature embryo and endosperm, AS of MORC7 (a gene implicated in epigenetic gene silencing), was markedly different. Long non-coding RNAs (lncRNAs) also underwent AS during the transition from milk seed to mature embryo and endosperm, with a complex gene structure, and were more extensively processed than predicted by current genome annotation. Exon retention of lncRNAs was enhanced in embryos. Searching all 5,515 lncRNAs in the NCBI genome annotation uncovered gene families based on highly conserved regions shared by groups of 3-35 lncRNAs. The homologies to other lncRNAs, as well as homologies to coding sequences, and the genomic context of lncRNAs provide inroads for functional analysis of multi-exonic lncRNAs that can be extensively processed during seed development.