Crop reproductive meristems in the genomic era: a brief overview

Azolla mediated alterations in grain yield and quality in Rice

Rice is one of the most important cereal crops worldwide. To boost its production in a sustainable manner, co-cultivation with Azolla species is often used to supplement its nitrogen (N) demands. However, beyond N nutrition, the physiological and developmental effects of azolla on rice remain unclear. This study investigates these mechanisms by analysing growth, inflorescence meristem transcriptomics, yield, and grain ionomics in rice plants grown alone (R) or with azolla (R + A) in non-limiting N conditions. During the vegetative stage, the presence of azolla increased allocation of resources to rice shoots without affecting root growth, while in the reproductive stage, it improved panicle architecture, with a 6% increase in length and up to 26% increase in panicle branching. Nevertheless, while this increase in panicle branching in R + A translated into a greater number of grains per plant, grain weight declined. As a result, yields were similar between R and R + A. There was also an azolla-induced increment in several mineral elements in R + A grains, with the notable exception of zinc, which declined by more than 30%. Finally, the presence of azolla altered the expression of several gene families, and in particular, it led to the upregulation of numerous transcription factors from the AP2/ERF, WRKY and NAM families. Interestingly, the presence of azolla also led to the upregulation of several genes (including WRKY transcription factors) involved in resistance to several pathogens and abiotic stresses. Overall, our results suggest that rice-azolla co-cultivation has implications that go beyond N-nutrition for sustainable intensification of rice production.

The ALOG family members OsG1L1 and OsG1L2 regulate inflorescence branching in rice

The architecture of the rice inflorescence is an important determinant of crop yield. The length of the inflorescence and the number of branches are among the key factors determining the number of spikelets, and thus grains, that a plant will develop. In particular, the timing of the identity transition from indeterminate branch meristem to determinate spikelet meristem governs the complexity of the inflorescence. In this context, the ALOG gene TAWAWA1 (TAW1) has been shown to delay the transition to determinate spikelet development in Oryza sativa (rice). Recently, by combining precise laser microdissection of inflorescence meristems with RNA-seq, we observed that two ALOG genes, OsG1-like 1 (OsG1L1) and OsG1L2, have expression profiles similar to that of TAW1. Here, we report that osg1l1 and osg1l2 loss-of-function CRISPR mutants have similar phenotypes to the phenotype of the previously published taw1 mutant, suggesting that these genes might act on related pathways during inflorescence development. Transcriptome analysis of the osg1l2 mutant suggested interactions of OsG1L2 with other known inflorescence architecture regulators and the data sets were used for the construction of a gene regulatory network (GRN), proposing interactions among genes potentially involved in controlling inflorescence development in rice. In this GRN, we selected the homeodomain-leucine zipper transcription factor encoding the gene OsHOX14 for further characterization. The spatiotemporal expression profiling and phenotypical analysis of CRISPR loss-of-function mutants of OsHOX14 suggests that the proposed GRN indeed serves as a valuable resource for the identification of new proteins involved in rice inflorescence development.