COVER The irrigation of rice fields by smallholder farmers in Bangladesh, like the one in Sylhet pictured here, has transformed this densely populated, once famine-prone land to a food-secure nation over the past three decades. This type of agriculture depends on groundwater withdrawals made possible by subsurface recharge by the highly seasonal rainfall. This cycle sustains irrigated food production under a changing climate. See pages 1258 and 1315.

Photo: K. M. Asad

ONLINE COVER A flower showing various genotypes of the monkeyflower species Mimulus parishii. Liang et al. identify a single nucleotide substitution in a gene that causes reduced flower coloration in a self-pollinated monkeyflower species. They find this mutation occurs in the mRNA rather than the elements that control gene transcription, leading to reduced protein translation. These results support the role of mutations affecting translation in natural phenotypic variation.

ONLINE COVER Waves of IgA Regulate the Intestinal Microbiota. This month’s cover depicts the dynamic interplay between immunoglobulin A (IgA) and the commensal microbiota in the intestinal lumen. Penny and Domingues et al. report that secretory IgA exhibits daily rhythms in its release from lamina propria plasma cells into the intestinal tract, which are controlled by signals provided by food and the circadian clock. These “waves” of IgA regulate the daily oscillations in the relative abundance of commensal gut microbes to help maintain gut homeostasis.

ONLINE COVER Flexing Biomolecular Muscle. Actuation of soft microrobots can be achieved through the application of miniature motors, such as artificial muscles. However, the integration of such actuators within soft microrobots requires assembly processes that are often slow and require multiple steps. Wang et al. have developed a rapid and cost-effective in situ fabrication process that integrates artificial muscles composed of molecular motors in a variety of microrobots. This month’s cover shows a microrobot manipulating a ball; its arms are sequentially controlled by light-responsive artificial muscles.

ONLINE COVER This week, Dolan et al. report that the coordinated mass secretion of mucus by goblet cells and ion transport by enterocytes drive crypt purging in the small intestine. The image is a colorized electron micrograph of a section through the duodenum showing a goblet cell filled with mucus granules and flanked by enterocytes.

ONLINE COVER A Sticky Situation. The image shows a Staphylococcus aureus bacterial biofilm adhered to plastic. Biofilms hinder antibiotic penetration and constitute a clinical challenge. Building on work showing that an added glycopeptide group improved vancomycin potency against Gram-positive bacteria, Blaskovich et al. here optimized these so-called “vancapticins”. The resulting compound displayed a low propensity for resistance development and was effective when dosed via different routes in numerous preclinical models of established Gram-positive bacterial infection, including against hard-to-treat biofilms. This class of antibiotics thus shows potential for addressing a current clinical need.