Floret-specific differences in gene expression and support for the hypothesis that tapetal degeneration of Zea mays L. occurs via programmed cell death

The maize （Zea mays） spikelet consists of two florets, each of which contains three developmentally synchronized anthers. Morphologically, the anthers in the upper and lower florets proceed through apparently similar developmental programs. To test for global differences in gene expression and to identify genes that are coordinately regulated during maize anther development, RNA samples isolated from upper and lower floret anthers at six developmental stages were hybridized to cDNA microarrays. Approximately 9% of the tested genes exhibited statistically significant differences in expression between anthers in the upper and lower florets. This finding indicates that several basic biological processes are differentially regulated between upper and lower floret anthers, including metabolism, protein synthesis and signal transduction. Genes that are coordinately regulated across anther development were identified via cluster analysis. Analysis of these results identified stage-specific, early in development, late in development and bi-phasic expression profiles. Quantitative RT-PCR analysis revealed that four genes whose homologs in other plant species are involved in programmed cell death are up-regulated just prior to the time the tapetum begins to visibly degenerate （i.e., the mid-microspore stage）. This finding supports the hypothesis that developmentally normal tapetal degeneration occurs via programmed cell death.

Exploiting viral vectors to deliver genome editing reagents in plants

Genome editing holds great promise for the molecular breeding of plants,yet its application is hindered by the shortage of simple and effective means of delivering genome editing reagents into plants.Conventional plant transformation-based methods for delivery of genome editing reagents into plants often involve prolonged tissue culture,a labor-intensive and technically challenging process for many elite crop cultivars.In this review,we describe various virus-based methods that have been employed to deliver genome editing reagents,including components of the CRISPR/Cas machinery and donor DNA for precision editing in plants.We update the progress in these methods with recent successful examples of genome editing achieved through virus-based delivery in different plant species,highlight the advantages and limitations of these delivery approaches,and discuss the remaining challenges.

Engineer and split an efficient hypercompact CRISPR–CasΦ genome editor in plants

The programmable CRISPR-Cas genome editing technology,adopted from prokaryotic adaptive immune systems,has revolutionized genome engineering in plants(Liu et al.,2022a).Many efforts have been made to improve the activity,specificity,and protospacer adjacent motif(PAM)variants of Class 2 Cas nucleases,such as Cas9,Cas12a,and Cas12b(Liu et al.,2022a).However,their large size(∼1000–1400 amino acids)poses a challenge in scenarios requiring a compact Cas nuclease,particularly in urgent situations like plant virus-induced genome editing(Cheuk and Houde,2018;Li et al.,2021;Varanda et al.,2021).

Genetic diversity for mycorrhizal symbiosis and phosphate transporters in rice

Phosphorus （P） is a major plant nutrient and developing crops with higher P-use efficiency is an important breeding goal. In this context we have conducted a comparative study of irrigated and rainfed rice varieties to assess genotypic differences in colonization with arbuscular mycorrhizal （AM） fungi and expression of different P trans- porter genes. Plants were grown in three different soil samples from a rice farm in the Philippines. The data show that AM symbiosis in all varieties was established after 4 weeks of growth under aerobic conditions and that, in soil derived from a rice paddy, natural AM populations recovered within 6 weeks. The analysis of AM marker genes （AM1, AM3, AM14） and P transporter genes for the direct Pi uptake （PT2, PT6） and AM-mediated pathway （PTll, PT13） were largely in agreement with the observed root AM colonization providing a useful tool for diversity studies. Interestingly, delayed AM colonization was observed in the aus-type rice varieties which might be due to their different root structure and might confer an advantage for weed competition in the field. The data further showed that P-starvation induced root growth and expression of the high-affinity P transporter PT6 was highest in the irrigated variety IR66 which a]so maintained grain yield under P-deficient field conditions.

Map-based cloning of the ALK gene,which controls the gelatinization temperature of rice

Gelatinization temperature (GT) is an important parameter for evaluating the cooking and eating quality of rice besides amylose content (AC). The inheritance of the genes affecting GT has been widely studied and is considered to be controlled by a major gene. Here, we report the map-based cloning of rice ALK that encodes the soluble starch synthase II (SSSII). Comparison between the DNA sequences from different rice varieties, together with the results obtained with digestion of the rice seeds in alkali solution, indicates that the base substitutions in coding se-quence of ALK may cause the alteration in GT.

A Bi-Functional Xyloglucan Galactosyltransferase Is an Indispensable Salt Stress Tolerance Determinant in Arabidopsis

Salinity is an abiotic stress that substantially limits crop production worldwide. To identify salt stress tolerance determinants, we screened for Arabidopsis mutants that are hypersensitive to salt stress and designated these mutants as short root in salt medium （rsa）. One of these mutants, rsa3-1, is hypersensitive to NaCI and LiCI but not to CsCI or to general osmotic stress. Reactive oxygen species （ROS） over-accumulate in rsa3-1 plants under salt stress. Gene expression profiling with Affymetrix microarray analysis revealed that RSA3 controls expression of many genes including genes encoding proteins for ROS detoxification under salt stress. Map-based cloning showed that RSA3 encodes a xyloglucan galactosyltransferase, which is allelic to a gene previously named MUR3/KAM1. The RSA3/ MUR3/KAMl-encoded xylogluscan galactosyltransferase regulates actin microfilament organization （and thereby con- tributes to endomembrane distribution） and is also involved in cell wall biosynthesis. In rsa3-1, actin cannot assemble and form bundles as it does in the wild-type but instead aggregates in the cytoplasm. Furthermore, addition of phal- Ioidin, which prevents actin depolymerization, can rescue salt hypersensitivity of rsa3-1. Together, these results sug- gest that RSA3/MUR3/KAM1 along with other cell wall-associated proteins plays a critical role in salt stress tolerance by maintaining the proper organization of actin microfilaments in order to minimize damage caused by excessive ROS.

Emerging Players in the Nitrate Signaling Pathway

Nitrogen （N）-based fertilizers are routinely used to increase agricultural productivity for both food and non-food uses of crops. Unfortunately, excess N fertilizers escape to the environment, leading to detrimental effects on the ecosystem and human health. Understanding how plants sense and respond to different N nutrients or metabolites to regulate metabolism, physiology, growth, and development is essential for sustained yields while reducing agriculture＇s environmental and economic costs.